chemical hazards, health risk assessment and exposure evaluation

Chemical Hazards: Health Risk Assessment and Exposure Evaluation

The companies belonging to the Royal Dutch/Shell Group of companies are separate and distinct entities, but in this document the collective expressions "Shell" and "Group" are sometimes used for convenience in contexts where reference is made to the companies of the Royal Dutch/Shell Group in general. These expressions are also used where no useful purpose is served by identifying the particular company or companies. This document is prepared by Shell Internationale Petroleum Maatschappij B.V. (SIPM) as a service under arrangements in existence with companies of the Royal Dutch/Shell Group; it is issued for the guidance of these companies and they may wish to consider using it in their operations. Other interested parties may receive a copy of this document for their information. SIPM is not aware of any inaccuracy or omission from this document and no responsibility is accepted by SIPM or by any person or company concerned with furnishing information or data used in this document for the accuracy of any information or advice given in the document or for any omission from the document or for any consequences whatsoever resulting directly or indirectly from compliance with or adoption of guidance controlled in the document even if caused by a failure to exercise reasonable care.

September 1995 SHELL HEALTH, SAFETY AND ENVIRONMENT COMMITTEE

The copyright of this document is vested in Shell Internationale Petroleum Maatschappij B.V., The Hague, The Netherlands. All rights reserved.

AMENDMENT RECORD SHEET

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Section No.

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TABLE OF CONTENTS

INTRODUCTION 1

1 HEALTH RISK ASSESSMENT 2

1.1 GATHERING INFORMATION ON CHEMICAL AGENTS (HRA Step 3) 4 1.1.1 Identification of chemical agents 4 1.1.2 Information on hazard 4 1.1.3 Nature and degree of exposure 7 1.1.4 Screening (compliance) and performance criteria 9

1.2 EVALUATING THE RISK TO HEALTH (HRA STEP 4) 11

1.3 DECIDING ON REMEDIAL (CORRECTIVE) ACTION (HRA Step 5) 13 1.3.1 Types of control measures 13 1.3.2 Examples of inadequate control 14 1.3.3 Examples of control improvements 14 1.3.4 Factors to consider in the selection of control measures 15

1.4 FURTHER READING 16

2 MONITORING OF CONTROLS 17

2.1 DEVISING A MONITORING STRATEGY 17

2.2 HAZARDOUS SUBSTANCES 17

2.3 MONITORING METHODS 18

2.4 TRIGGER POINTS 19

2.5 MANAGEMENT OF EXPOSURE MEASUREMENT 21

2.6 SUPPLEMENTARY MONITORING METHODS 21

3 EXPOSURE MEASUREMENT 23

3.1 AIR MEASUREMENT 23 3.1.1 Selection of an appropriate sampling and analytical methodology 23 3.1.2 Validation of sampling and analytical methods 23 3.1.3 Records 23 3.1.4 Types of exposure measurement survey 23 3.1.5 Personal exposure protocols 24 3.1.6 Interpretation of results (checking compliance) 25

3.2 BIOLOGICAL MONITORING 26

3.3 QUALITY ASSURANCE 26 3.3.1 Good practice 26 3.3.2 Managing critical quality control points 27

3.4 COMPETENCE 27

3.5 FURTHER READING 27 3.5.1 Air measurement 27

HSE 071 i September 1995

3.5.2 Biological monitoring 28 3.5.3 Quality assurance 28

3.6 ACRONYMS 28

APPENDIX 1 INTRODUCING TOXICOLOGY - AN OUTLINE 29

APPENDIX 2 COMMON TOXICITY TERMS 31

APPENDIX 3 OVERVIEW OF EXPOSURE MEASUREMENT STRATEGY 34

APPENDIX 4 CALCULATION FOR COMBINING FRACTIONAL EXPOSURE MEASUREMENTS TO ALLOW COMPARISON WITH A SPECIFIED REFERENCE PERIOD 35

1 UNITS OF MEASUREMENT 35

2 CALCULATIONS 35

APPENDIX 5 ADDRESS LIST 37

ii HSE 071 September 1995

HSE 071 1 September 1995

INTRODUCTION

The Shell HSE Committee publication on 'Health Risk Assessment' issued in September 1994, provides general advice on carrying out Health Risk Assessment (HRA) of chemical, physical, biological and ergonomic health hazards found in the workplace, in a structured manner. HRA is the tool for implementing the Hazard and Effects Management Process (HEMP) as it relates to health hazards.

The Health Risk Assessment guide is referred to as the 'General Guide' throughout this document and Health Risk Assessment as HRA.

This publication on 'Chemical Hazards: Health Risk Assessment and Exposure Evaluation' supplements the General Guide by providing advice on assessing risks to health arising from chemical agents in the workplace. The information is advisory and is intended for the use of Assessment Teams.

The guide is divided into three parts as follows:-

Part 1: Health Risk Assessment:

Part 1 expands on the following HRA Steps introduced in the General Guide focusing on chemical hazards:-

Step 3: Gathering Information on chemical agents, personal exposures and screening and performance criteria. (HEMP: Identify)

Step 4: Evaluating the risk to health. (HEMP: Assess)

Step 5: Deciding on remedial action (control measures) to reduce exposures to 'as low as reasonably practicable' (ALARP). (HEMP: Control and Recover)

In addition to these Steps, the assessment should be recorded (Step 6) and reviewed for continuing validity (Step 7).

Part 2: Monitoring of Controls (HEMP: Monitoring and corrective action)

Monitoring of controls to check on their continuing effectiveness is necessary to prompt corrective action and thereby ensure that exposures continue to be controlled to ALARP. Part 2 recommends monitoring methods, together with identifying triggers for when and how often they should be implemented.

Part 3: Exposure Measurement

Collection of quantitative exposure data may be necessary as part of the HRA itself or as part of the monitoring of controls. Part 3 provides an overview of what is involved in data collection and its subsequent interpretation under the headings air measurement, biological monitoring, quality assurance and competence.

1 HEALTH RISK ASSESSMENT

The implementation of HRA involves the following steps:-

Details on the process of HRA are given in the Shell HSE Committee publication on Health Risk Assessment, September 1994, which is referred to as the 'General Guide' throughout this document.

HSE 071 September 1995

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In order to assist in the HRA of chemical hazards additional guidance is given in Section 1 specific to chemical agents, focusing on HRA Step 3, gathering information, Step 4, evaluating the risk to health, and Step 5, deciding on remedial action.

This document deals with workplace risk assessment of chemical hazards. Risk assessment terminology associated with chemical agents is also defined by the European Union in the Regulation on Risk Assessment of Existing Substances. For completeness and comparison purposes, the definitions associated with this Regulation are given as a footnote to Appendix 1.

1.1 GATHERING INFORMATION ON CHEMICAL AGENTS (HRA Step 3)

HRA begins by gathering the following information:-

• agents in the workplace and their harmful effects;

• the nature and degree of exposure to the agents;

• screening and performance criteria against which to evaluate the risk to health. The guidance applies to toxic, corrosive, irritant and sensitising aspects. Hazards resulting from flammability, explosivity or oxidising (as it relates to fire propagation) characteristics need to be addressed separately.

1.1.1 Identification of chemical agents Create an inventory of all chemical agents stored/used/produced in each work area and obtain health hazard information on each. Maintain a register of manufacturer's/suppliers health and safety data sheets.

To ensure that the list is comprehensive, consider:-

• feedstocks and additives;

• intermediates and by-products;

• final products;

• ancillary chemicals used in the process, e.g. catalysts, vessel flushing agents, solvents, acids and alkalis used for pH adjustment, drilling mud chemicals, biocides, surfactants;

• waste products, e.g. residues, gaseous emissions, dirty rags, empty contaminated containers;

• proprietary products e.g. cleaning agents, oils and greases, paints, degreasing agents, glues;

• building, plant and equipment construction materials e.g. insulation and fire retarding materials, paints, gaskets and packing materials;

• chemical agents produced as a result of tasks or processes, e.g. welding fumes and gases, oil mist, vehicle exhausts.

1.1.2 Information on hazard By way of background information on the hazards of chemical agents, an introduction to toxicology and a list common toxicity terms are given Appendix 1 and 2 respectively.

Advice on where to obtain information on the harmful effects of chemical agents is given below. In addition, guidance on the routes of in-take and key physico-chemical properties of interest when assessing exposures is provided.

a) Sources of information Information may be obtained from, for example:-

• manufacturer's and supplier's health and safety data sheets, labels or manuals on products;

• databases or published texts;

• Operating Company and Service Company guidance material; or advice may be obtained from:-


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• occupational health advisers such as occupational hygienists, toxicologists, occupational health physicians;

• organisations with knowledge and experience of the activity or operation, e.g. industry associations, government health and safety advisory bodies.

b) Routes of exposure Exposure can occur via three routes:-

• Inhalation (via the lungs);

• Skin contact, either directly or from contaminated surfaces or clothing. Some chemicals are able to enter the body through intact skin, e.g. xylene, toluene, phenol, hydrofluoric acid. In addition, tasks involving high pressure equipment may result in injection of chemicals through the skin, e.g. paint spraying, grease injection, or by contact with sharp objects which are themselves contaminated;

• Ingestion (via the mouth), either directly or by consuming contaminated food or drink. Smokers are vulnerable to transferring chemical agents on their hands to their mouth if they have not ensured their hands are clean before smoking a cigarette, as are nail biters.

c) Physical and chemical properties

Both the physical and chemical properties of a chemical agent may affect its intrinsic hazard or the potential for an increase in the exposure level.

General considerations are:-

• different physical forms of the same chemical agent may present different hazards, e.g. a granule or flake may present negligible hazard but, when ground into dust of a respirable size, it may be very hazardous;

• many chemicals contain impurities which could present a greater hazard than the substance they contaminate, e.g. crystalline silica is often present in mineral-based materials which would otherwise be of low toxicity;

• fibres which are toxic because of their length and diameter (see Particulates below);

• some chemical processes may be known to cause ill health but the causative agent(s) may not have been identified, e.g. isopropyl alcohol production using the strong acid process which causes lung cancer;

• additive or synergistic effects (see Appendix 2) of mixtures, e.g. the Special Boiling Point Solvents (SBPs) contain n-hexane in concentrations ranging from <1 to 50% where n-hexane is known to cause effects on the nervous system;

• the toxicity of a solvent carrier may enhance skin penetration of the 'active' chemical. Some specific items are:-

• Gases/vapours - Relative vapour density

The weight of a specific volume of a gaseous chemical agent compared to the weight of the same volume of air.

If the relative vapour density of a gas is greater than 1, the gas will sink and tend to collect at floor level or in depressions. Such collection can result in unexpected high exposures as well as a potential fire and explosion hazard for those which are flammable. In some circumstances, the gas may completely replace air, including the oxygen which is essential for life, leading to asphyxiation (suffocation).

For low concentrations of gases or vapours usually involved in occupational exposures, unless the result of an incidental release, such separation does not occur.

• Liquids/solids - Vapour pressure

The pressure of a vapour produced by a liquid or solid at a specified temperature and is usually expressed in Pascals (Pa) or millibar (mb) at 20°C. Chemicals with a high vapour pressure are described as volatile.

The higher the vapour pressure the higher the potential concentration in air. The vapour pressure of a chemical increases with temperature.

The boiling point of a chemical agent is a useful indicator of its volatility. One that boils at or below the reference temperature and pressure of 20°C and 101.3 kPa means it is usually present in gaseous form. Thus the closer the boiling point of a liquid is to these reference levels the greater its vapour pressure and hence its tendency to vaporise.

- Solubility and molecular weight

The solubility of a chemical in the surface layer of the skin is the major determinant of the potential for a substance to be absorbed into the body via this route. Fat soluble compounds are generally well absorbed by the skin whilst water soluble substances are not. In addition, the size of the molecule is also an important factor in skin absorption. Molecular weight or, more accurately, molecular volume, will affect absorption, although to a much lesser degree than solubility. Large molecules (molecular weight > 500) will only be absorbed very slowly, if at all.

Those chemicals easily absorbed via the skin are usually given a 'skin' notation in the references listing occupational exposure limits (see 1.1.4.).

• Mixtures Volatile mixtures present special problems in terms of the concentration of individual components in air and the possibility of additive and synergistic effects. It is important to know the different components so that the health effect can be assessed for the relevant ones. See Appendix 2 for a definition of 'Additive effect' and 'Synergistic effect'. In addition, the different components may have differing vapour pressures.

• Particulates These are divided into:-

- dust: solid particles in air which may be amorphous, crystalline or fibrous

- fume: condensed solids in air

- mist: liquid droplets in air

- smoke: small gas borne particles derived from incomplete combustion

Aerosol is a general term for solid or liquid airborne particulate matter.

- Particle size and shape

In respect of inhalation, the particle size and shape play a significant role in the ability of a particulate to become and remain airborne, as well as their ability to enter and penetrate into the respiratory system. In simplified terms the following applies:-

o particulates that have Stokes diameter of less than 100 micrometres can enter the respiratory tract and are termed the 'Total Inhalable Fraction'*


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o < 7 micrometres diameter can be inhaled deep into the lungs and are referred to as the 'Respirable Fraction'*. This size range is of particular relevance to substances which cause pneumoconiosis or related effects.

* CEN 481: Workplace atmospheres - Size fraction definitions for measurement of airborne particles.

o fine fibrous dusts with an aspect ratio (length to breadth) of at least 3:1 become easily aligned with the airstream of inhaled air and are regarded as respirable;

o particles of irregular shape are more easily trapped in the mucous lining of the upper respiratory tract.

1.1.3 Nature and degree of exposure Information on exposure should include:-

• who is exposed;

• exposure level; and

• related circumstances (work practices, existing controls). For the chemical agents to which people are exposed see 1.1.1.;

Prior to commencing a review of exposure to each chemical agent identified within an Assessment Unit*, it may be possible to simplify the process by grouping chemicals on the basis of their hazardous properties and the way they are being handled.

* An Assessment Unit may comprise for example a small complete operational site, a self-contained segment of a large or complex site, or a group supporting a single business process, so defined as to assist in the management of HRA within an organisation.

Be alert to individual chemicals in mixtures which pose specific hazards. Examples of these are:-

• Liquefied Petroleum Gas (LPG) normally comprises a mixture of C3 to C5 saturated hydrocarbons. However, LPG derived from 'cracking processes' may contain 1,3-butadiene which is classified by IARC (International Agency for Research on Cancer) as Category 2B probably carcinogenic to humans (IARC monograph no 54, 1992).

• Chemical solvents can be grouped and assessed on the basis of their functional composition, e.g. alcohols, ketones, aromatic solvents, paraffinic solvents. However, the solvents may contain components with the potential for causing serious ill-health effects, e.g. benzene (a carcinogen) or n-hexane (a nervous system toxin).

a) Who is exposed

Employees and other workers should be assigned to Job Types based on similar tasks and thus having similar potential for exposure. Job Types may represent one or more jobs, reflecting likely exposure patterns (See General Guide Steps 2.4 Job Types and 2.5 Tasks and Hazardous Agents). Job Types which involve similar tasks can be combined.

Ensure that all potential exposures to hazardous chemical agents have been identified for assessment by reviewing:-

• the individual operations which are carried out, e.g. manufacturing, processing, blending, storage, distribution, transport, disposal;

• the specific activities/tasks, e.g. sampling, filter changing, pump maintenance;

• the personnel involved either directly or indirectly, e.g. process operators, maintenance technicians, cleaners, laboratory technicians, office workers, supervisors;

• all others including contractors, temporary staff including students and trainees, visitors or persons working in the vicinity of an activity, community or site neighbours;

• all the potential points of release of the chemical agents in question, e.g. vents and exhausts, leaking pumps, valves, in addition to those tasks involving potential exposure.

Some persons may be at increased risk for whom special consideration is required and include:-

• pregnant women and nursing mothers;

• untrained or inexperienced persons (e.g. new recruits, temporary workers);

• persons working in confined or poorly ventilated spaces;

• persons with pre-existing conditions (e.g. bronchitis, sensitised to the chemical concerned, asthmatics);

• persons receiving medications which might increase their susceptibility to toxic effects;

• persons suffering from malnutrition or a chronic infection;

• smokers, who may be at increased risk due to additive or synergistic effects. All such persons should be identified and appropriate action taken.

b) Exposure Level

The personal exposure level to a particular chemical agent is established by estimating:-

• the magnitude of exposure (e.g. breathing zone concentration of the agent or opportunity for skin contact)

• the frequency of exposure (times per day, week, month, year);

• the duration of exposure (minutes or hours per day); taking into account the likelihood of an increased level of exposure during normal operations or resulting from abnormal conditions or foreseeable emergencies.

Exposure levels may be estimated by direct measurement or from relevant data and experience. Refer to Part 3 'Exposure Measurement' for an outline on measurement strategies.

For both direct measurement and qualitative assessment, observation of the tasks involving potential exposure is essential. This should also include discussion with supervisors and staff doing the work to ensure a clear understanding of what is involved and any potential for loss of control, thereby increasing the potential for exposure.

In addition to routine work, also consider activities such as one-off maintenance jobs, plant start-up, shutdowns, commissioning, turn-arounds, etc.

• Magnitude of exposure Refer to Section 1.1.2. for those chemical and physical properties which affect the potential concentration of a chemical agent in air or its ability to be absorbed via the skin. For those chemical agents which cause an effect by direct contact, e.g. irritants, corrosives and sensitisers, consider the potential for contact with the skin, eyes or respiratory tract.

Where there is a combination of exposures to different chemical agents, the combined health effect should be considered (see Appendix 2 Additive and Synergistic Effects).

• Frequency and duration of exposure


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The pattern and total time of exposure during the entire work period can be determined by observing the task(s)/process, by asking relevant supervisors and the people actually doing the work.

Remember that certain Job Types, e.g. maintenance technicians, may carry out many tasks in any one work period and also across more than one Assessment Unit, particularly in a large chemical plant or refinery. Exposures may be to the same, similar or totally different chemical agents. Exposure times in such circumstances will also vary considerably.

• Likelihood of an increase in exposure Many changes in process or equipment could result in increases in potential exposure, typical examples being:-

- change in physical form of the agent as a result of the task (e.g. a liquid changed to an aerosol by spraying, a solid changed to a respirable dust by grinding);

- an increase in the exposure period as a result of a greater workload;

- pump/flange/equipment leakage;

- faulty high level sensor leading to vessel overflow;

- reduced airflow into local exhaust ventilation system owing to, e.g. a blocked filter, faulty fan operation, system leakages or mal-adjustment of ventilation ducting dampers;

- higher in-take during heavy physical labour.

c) Related circumstances (work practices, existing controls)

The level of exposure is influenced by the effectiveness of existing control measures and their usage by staff.

See the General Guide item 3.2.3. for general advice on reviewing existing control measures and judging their adequacy. Additional information in respect of control measures for chemical agents is given under Sections 1.1.4. and 1.3. below.

1.1.4 Screening (compliance) and performance criteria Exposure should be controlled to a level 'as low as reasonably practicable' (ALARP) and should, in any case, be less than the occupational exposure limit (OEL) for the agent in question. In addition, the recommended measures to achieve a level ALARP for that agent should be specified. The OEL and specifications for control are known as screening (compliance) and performance criteria. These criteria may be in place prior to the HRA commencing, or may be introduced as a result of an unsatisfactory level of control identified during the HRA.

Definitions of OELs for chemical agents are given below. For reference to specifications for control measures see the General Guide item 3.3.; further examples of controls are given in Section 1.3. below.

a) OEL: Personal exposure - air measurement

Many countries have identified Occupational Exposure Limits (OELs) for various chemical agents - units are in parts per million (for gases and vapours), milligrams per cubic metre (for all except fibrous dusts) or fibres per millilitre of air (for fibrous dusts). In general, the limits comprise:-

• a Time-Weighted Average (TWA) exposure: the TWA concentration for a normal 8-hour workday and a 40-hour workweek, to which nearly all workers may be repeatedly exposed, day after day, without adverse effect;

• a Short Term Exposure Limit (STEL): this is applied to chemicals with acute effects and, in general, is a maximum allowable exposure over a 15 minute period; and, in some cases,

• a Ceiling Limit: the concentration that should not be exceeded during any part of the working exposure.

Where a country has no OEL for a substance, Shell Companies are recommended to refer to the documentation and Threshold Limit Values (TLV) list published annually by the American Conference of Governmental Industrial Hygienists (ACGIH). Other reference sources are the European Union Indicative Limit Values (ILVs - these are currently draft limits), individual country's limits such as the United Kingdom's Occupational Exposure Standards (OESs) and Maximum Exposure Limits (MELs), the Netherland's MAC waarden, the German Maximale Arbeitsplatzkonzentrationen (MAKs) and Technical Exposure Limits (TRKs).

If no OEL exists for a particular substance its supplier should be requested to provide a working limit, together with evidence to support that limit. Alternatively, a request for an advised limit may be made to Occupational Health Advisers in the Service Companies.

By exception, Shell Occupational Health Advisers may recommend an OEL lower (i.e. more stringent) than other published limits for a substance where the lower limit is readily achievable, or evidence exists to justify it.

b) OEL: Personal Exposure - Biological Monitoring

Biological Limit Values (BLVs) have been set for a number of chemical agents. A BLV is the maximum allowable concentration in body fluids of workers of a chemical or its metabolite* which does not cause adverse effects. Shell Service Company recommended BLVs are given in Report HSE 94.014 Laboratory Tests for Biological Monitoring and Biochemical Effect Monitoring available from SIPM-HSE/50.

* A metabolite of a substance is either a breakdown product or modified (more soluble) form suitable for excretion by the kidney in the urine or by the liver into the intestine.


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1.2 EVALUATING THE RISK TO HEALTH (HRA STEP 4)

Using the information obtained in Step 3, the risk to health is evaluated by making a judgement on:-

• the 'severity' of the possible ill-health effect form over-exposure to the agent to give a Hazard Rating;

• the 'chance of over-exposure' to give an Exposure Rating; The 'Hazard' and 'Exposure' Ratings are then evaluated in a Risk Matrix. Guidance on this process is given in the General Guide.

The Exposure Rating indicates whether or not exposures to a particular agent are adequately controlled when compared against the relevant screening and performance criteria. Its purpose is to assist in deciding when additional control measures should be implemented to reduce exposures. When combined with the Hazard Rating in the Risk Matrix, priorities for action can be determined.

For ease of reference the Hazard Ratings, Exposure Ratings and Risk Matrix are reproduced below.

Table 1: Hazard Ratings

HAZARD RATING

DEFINITION(1) in terms of potential to cause 'Harm to People'(2)

0 NO INJURY OR DAMAGE TO HEALTH 1 SLIGHT INJURY/ILLNESS: Commonly causing nuisance not

affecting work performance or causing disability.

- e.g. low toxicity dusts. 2 MINOR INJURY/ILLNESS: Affecting work performance, such as

restriction of activities (Restricted Work Case), or a need to take a few days to fully recover (Lost Workday Case).

- Agents which have limited health effects which are reversible, e.g. alcohols, many hydrocarbons

3 MAJOR INJURY/ILLNESS: Resulting in a Permanent Partial Disability or affecting work performance in the longer term, such as a prolonged absence from work.

- Agents which are capable of irreversible damage without serious disability, e.g. amine skin sensitisers.

4 PERMANENT TOTAL DISABILITY OR FATALITY: - Agents which are capable of irreversible damage with serious

disability or death, e.g. hydrochloric acid, sodium hydroxide (caustic soda), hydrogen sulphide, asbestos, benzene.

5 MULTIPLE FATALITIES - Agents as in 4.

(1) Refer to the SHC Guide on Health Performance Reporting, 1993, Appendix 1 for the definition of Work Injury, Occupational Illness, Restricted Work Case, Lost Workday Case, Permanent Partial Disability, Permanent Total Disability and Fatality

(2) Refer to the SHC Guide Incident Potential Matrix, 1991, Appendix 2, Table 2a.

Table 2: Exposure Ratings

EXPOSURE RATING

DEFINITION

A. Very Low Negligible exposures B. Low Exposures below the OEL are controlled and likely to remain so in

accordance with screening and performance criteria. C. Medium Exposures approaching the OEL, currently controlled to meet screening

and performance criteria, but control cannot be assured. D. High Exposures at or above the OEL, not adequately controlled to meet

screening and performance criteria and continuously/regularly exceed OELs.

E. Very High Exposures well above the OEL likely to result in health damage to persons exposed.

Table 3: Risk Matrix

Potential consequence of exposure to the hazardous agent as determined by the agent's HAZARD RATING

Measure of exposure as determined by the EXPOSURE RATING

RATING HARM TO PEOPLE VERY LOW

(A)

LOW

(B)

MED

(C)

HIGH

(D)

VERY HIGH

(E)

1 Slight injury/illness

2 Minor injury/illness

3 Major injury/illness

4 Permanent total disability/fatality

5 Multiple fatalities

In respect of chemical agents the Exposure Rating may be further defined as Category I or Category II exposures:-

• Category I : < 0.1 x OEL

• Category II: > 0.1 x OEL

Category I applies to the Exposure Rating 'A: Very Low'. Category II applies to the remaining Exposure Ratings. Where exposures fall within the range 0.1-1 x OEL, i.e. Exposure Ratings 'B: Low' and 'C: Medium', judgement can be exercised in the selection of methods to monitor controls to ensure their continuing integrity - see Part 2, Table 4 'Monitoring of controls : what method versus when to carry out'.


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1.3 DECIDING ON REMEDIAL (CORRECTIVE) ACTION (HRA Step 5)

Where the need for additional control measures is identified to reduce the risk, a systematic review of all control options should be made with a view to controlling exposures to ALARP. 'Controls' equate to the term 'barriers' in HEMP.

Part 2 'Monitoring of Controls' provides guidance on the need for measures to monitor the continuing integrity of the control options in use.

The following provides examples of exposure control measures by way of illustration of:-

• types of controls (item 1.3.1.);

• what are considered inadequate controls (item 1.3.2.);

• recommended control improvements (item 1.3.3.); and

• factors to consider in the selection of control measures, including examples of recovery measure for the mitigation of effects should controls fail (item 1.3.4.).

1.3.1 Types of control measures The hierarchy of controls comprises:-

- elimination of the hazard

- substitution of the hazard

- engineering measures

- procedural measures

- personal protective equipment

- personal hygiene

Examples are:-

• Substitution of the hazard, for example:- replace with a less hazardous substance, introduce a non-dusting powder for one that is friable.

• Engineering (plant and equipment), for example:- - totally enclosed process and handling systems. Examples of equipment used to

contain products are mechanical seals, Dopak sampling systems; - plant or processes which minimise generation of, or suppress or contain, the

hazardous dust, fume, etc. and which limit the area of contamination in the event of spills and leaks. Examples are temperature controllers, pv valves, bunding and enclosed draining systems;

- enclosure with local exhaust ventilation, examples are fume cupboards, tipping cabinets, with filters or scrubbers;

- general ventilation.

• Procedural, for example:- - provision of information, instruction and training;

- the use of Permits to Work for controlling hazardous operations;

- systems of work which minimise generation of, or suppress, the emission to atmosphere of the hazardous chemical, e.g. damping down dusts, controlling temperatures and pressures;

- minimising the number of employees exposed and exclude non-essential access;

- minimising the period of exposure;

- decontamination of walls, surfaces;

- safe storage and disposal of hazardous chemicals;

- prohibition of eating, drinking, smoking, in the work room;

- facilities for washing, changing and separate storage of personal and work clothing, including arrangements for laundering contaminated clothing;

• Personal Protective Equipment (PPE) Examples of situations where the use of suitable PPE may be appropriate include:- - where it is presently not technically feasible to achieve adequate control of

exposure by engineering or procedural measures alone;

- where a new or revised assessment indicates that PPE is necessary to safeguard health until such time as adequate control is achieved by other means;

- where entry into high concentrations is unavoidable, e.g. because of plant failure, the only practicable solution in the time available may be the provision and use of PPE;

- where exposure occurs for short periods involving a small number of people and where further process control measures are not reasonably practicable.

In each of these cases the use of PPE would be considered as a reasonably practicable option.

• Personal hygiene, facilities for:- - washing and changing personal and work clothing;

- separate storage of clothing;

- arrangements for laundering contaminated clothing.

1.3.2 Examples of inadequate control The following situations are examples of where exposures are likely to present a risk to health:-

- collection of samples of hazardous substances or process streams from open systems;

- failure to decontaminate systems before opening for maintenance;

- open bench cutting/shaping gaskets containing asbestos by sawing or grinding;

- filling drums with volatile hydrocarbons without delivery and ventilation controls;

- dumping drilling mud chemicals into a mixing hopper which is not fitted with effective local exhaust ventilation;

- loading volatile products into road tankers without vapour recovery systems.

- dumping of catalysts from reactors without controlling dust emissions;

- poorly maintained and non operational engineering controls.

In each of these cases it would be reasonably practicable to introduce additional control measures to reduce exposures to Category I.

1.3.3 Examples of control improvements The following are examples of current good practice from Shell operations:-


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- the replacement of hydrazine solutions used as an oxygen scavenger in boiler water treatment by alternative less hazardous proprietary chemicals, due to the potential carcinogenicity of hydrazine;

- the replacement of chlorinated hydrocarbon degreasing agents with water soluble alternatives;

- installation of contained sampling systems e.g. Dopak-type;

- use of double-mechanical seals on pumps or the use of canned pumps;

- modification of batch processes to 'closed reactor' technology;

- the removal of harmful gases, vapours, fumes or dusts at the point of generation by the use of local exhaust ventilation, wherever practicable, e.g. dust collection systems for catalyst loading/dumping operations, welding fumes;

- the formalisation by procedure of the provision of information on the health hazards of chemical agents used by staff and the measures to be taken to avoid exposure;

- the prevention of eating, drinking or smoking where chemical agents are stored, handled or used.

1.3.4 Factors to consider in the selection of control measures • Future maintenance needs, for example:-

- easy access to engineering control systems which require routine inspection;

- availability of competent persons for checking and maintaining ventilation systems, e.g. laboratory fume cupboards, dumping cabinets, welding fume extractors, mixing vessel extractors;

- personal protective equipment, particularly respiratory protective equipment, require considerable back-up in terms of training, supervision and maintenance, if it is to provide the intended level of protection. Incorrect selection, fitting and insufficient use all contribute to over-exposure.

• Measures for ensuring that the controls are used and maintained, for example:- - adequate and competent supervision to ensure that appropriate control measures

are correctly used;

- periodic checks and procedures to ensure that any defects in control measures are quickly identified, immediately reported and corrections made promptly;

- arrangements for maintenance to include schedules for inspection and testing of control equipment and associated records.

• Recovery measures to mitigate effects of loss of control, for example:- - trained people and availability of equipment to minimise materials release and to

contain/recover that which has been released;

- written emergency procedures in place and staff trained to cope with any foreseeable incident;

- sufficient and suitable personal protective equipment;

- provision for the prompt decontamination of personnel and personal protective equipment, e.g. eye wash baths, emergency showers, wash rooms, spare clothing;

- prior consideration to safe methods for disposal of the chemical agent(s) and any contaminated personal protective equipment.

1.4 FURTHER READING

The following are ADDITIONAL references to those listed in Appendix 8 of the General Guide; the latter should also be consulted. For details of the acronyms and contact addresses refer to Section 3.6. and Appendix 5 respectively.

• UK-HSC Control of Substances Hazardous to Health (COSHH) - General Approved Code of Practice. Fourth edition 1993. ISBN 0-11-882085-0.

• UK-HSE HS(G)97 - A Step by Step Guide to COSHH Assessment. 1993. ISBN 0-11-886379-7.

• UK-HSE HS(G)37 - An Introduction to Local Exhaust Ventilation. 1993. ISBN 0-11-882134-2.

• UK-HSE HS(G)54 - The Maintenance, Examination and Testing of Local Exhaust Ventilation. 1990. ISBN 0-11-885438-0.

• ACGIH Industrial Ventilation - A Manual of Recommended Practice. 21st Edition.

• UK-HSE HS(G)53 - Respiratory Protective Equipment - a Practical Guide for Users. 1990. ISBN 0-11-885522-0.

• SIPM Design and Engineering Practices (DEPs) publications


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2 MONITORING OF CONTROLS

This Section proposes a strategy for checking that measures in place for controlling risk are adequate and remain effective. This forms part of HRA Step 5 - Decide on remedial action, and equates to the monitoring and corrective action steps in HEMP. In addition, the role and application of exposure measurement is explained as one of several monitoring methods. Advice on how to carry out exposure measurement is given in Section 3.

The strategy is applicable to all workplace situations and is based on an action level below which only minimum actions are required.

There are a number of trigger points which lead to specified actions for direct and indirect evaluation of control.

2.1 DEVISING A MONITORING STRATEGY

The important issues which have a bearing on the strategy are:-

• the need for reliable estimates of exposure for the HRA;

• the need to identify and apply controls which keep exposure to ALARP and, in any event, below the Occupational Exposure Limit (OEL). The terminology for OELs is explained in 1.1.4.a.;

• the need to show that exposure is unlikely to exceed the OEL;

• the need to recognise failure of controls and take prompt remedial action.

2.2 HAZARDOUS SUBSTANCES

Chemical agents of particular strategic concern are those which:-

• cause irreversible harmful effects e.g. carcinogens;

• are absorbed through the lungs or skin;

• have an exposure response relationship which is ill defined;

• have stringent OELs;

• have poor warning properties;

• are volatile. Benzene, as an example, is found widely in the oil and petrochemical industry. It may be present in streams at low concentrations and may exist as a feedstock or product. It may be used in dedicated or general purpose plant, sometimes by the drum. Transfer can be by pipeline, road, rail or by ship.

2.3 MONITORING METHODS

Exposure measurement is one of nine procedural and technical methods for monitoring exposure.

As a general rule, as exposures move away from the OEL there is less need for measurement. At the extremes, exposure is either insignificant or clearly unacceptable.

The following monitoring methods apply to all situations:-

1. Health risk assessment, which specifies the controls, plus any need for exposure measurement and health surveillance. The HRA should identify whether exposures are Category I (less than 0.1 x OEL) or Category II (more than 0.1 x OEL). Refer to section 1.2. above.

2. Baseline exposure evaluation, which provides the data on which the assessment of risk is based.

3. Visual inspection, which provides daily checks on obvious control measures. 4. Examination and test, which provides a thorough regular check on the performance

of plant and equipment used to control exposures, e.g. ventilation performance and reusable respiratory protective equipment.

5. Process audit, which provides an in-depth evaluation of plant control and operational performance relative to company technical standards.

The following are used when required:-

6. Routine exposure measurement, in the form of personal sampling and checks of compliance with the OEL (see 3.1.4.c.).

7. Investigation, to determine the causes of failure to control exposure. 8. Biological monitoring, to give an index of individual intake. 9. Health surveillance, to detect, trace and quantify harmful effects. If any of the above monitoring methods indicate that exposures are not controlled to a level ALARP, then appropriate remedial action to regain control should be identified and implemented.


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2.4 TRIGGER POINTS

In this strategy, the following triggers are recommended for implementing the various monitoring methods (see also Table 4):-

• a minimum yearly reassessment for carcinogens and others agents posing long term irreversible hazards;

• a minimum 5-yearly reassessment;

• a minimum annual examination and test;

• a change in situation, e.g. a new work process, new pattern of work, revised appreciation of hazard and risk;

• unknown exposure;

• Category II exposures;

• Category II exposures that have a probability of 5% or more of systematically exceeding the OEL (refer to 3.1.6. Air measurement: interpretation of results);

• adverse health surveillance findings. Corrective action may be triggered by:-

• exposures not ALARP;

• failure identified by examination and test;

• failure identified by visual inspection;

• failure identified by audit;

Table 4: Monitoring of controls: what method versus when to carry out

Monitoring Method Methods 1-5 apply to all situations Methods 6-9 apply when required

When to carry out

1. Health risk assessment - Category I, every 5 years - a change in situation - Category II, consider more frequently*

2. Baseline exposure evaluation - unable to categorise exposure 3. Visual inspection - all situations, daily 4. Examination and test - all situations, at least annually* (respiratory

protective equipment at least quarterly) - plant start-up

5. Process audit - Category I, every 5 years - Category II, consider more frequently*

6. Routine exposure measurement (see 3.1.4.c.)

- consider* for Category II

7. Investigation - exposure data shows a probability that 5% of samples or more systematically exceed the OEL

- biological data shows a probability that 5% of samples or more systematically exceed the OEL

- recognition of adverse health effects 8. Biological monitoring - consider* for Category II

- exposure is unknown 9. Health Surveillance - pre-employment

- Category I, basic occupational health record - Category II, comprehensive health record - record of known or suspected high exposure - incidents following loss of controls

Results of monitoring of controls which will trigger corrective action

- exposure is not ALARP - fails visual inspection - fails examination and test - fails technical audit

* The terms 'at least', 'consider' and 'consider more frequently' indicate the need for a local decision on the need for linking monitoring to risk (see item 1.2. Evaluating the risk to health).


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From Table 4 it can be seen that there are only three occasions when exposure measurement, for company purposes, is appropriate, i.e.:-

• when baseline data are required (monitoring method 3);

• for routine measurement, when exposures are Category II, if considered necessary (monitoring method 6);

• when investigation is required, and then only if measurement is appropriate (monitoring method 7).

2.5 MANAGEMENT OF EXPOSURE MEASUREMENT

Implementation of exposure measurement to obtain quantitative data needs to be managed in order to achieve the maximum benefit from the effort expended. The main features are:-

• the requirement for measurement is determined as part of the HRA;

• if exposure is not known it may be determined by analogy with previous measurements in similar situations, or it should be measured as the baseline;

• the exposure should be ALARP. If not, this should first be achieved by modification of the control measures before measurement is undertaken;

• when exposure is ALARP and Category I the only action is to ensure that the HRA remains valid;

• when exposure is Category II there may be a requirement for routine exposure measurement (see 3.1.4.c.);

• if the exposure data obtained from routine measurement show Category II exposures with stability within the range 0.1 - 1 x OEL at the 95% probability level (see 3.1.6.) and exposures are controlled to ALARP, repeated measurement is discontinued. The need for future measurement is determined by HRA;

• if routine exposure measurement data show less than 95% compliance, the situation needs to be investigated;

• if investigation shows that the deficiency is systematic the situation should be reassessed and the controls reviewed.

Refer also to Section 3, which provides an overview of what is involved in the collection of quantitative exposure data.

2.6 SUPPLEMENTARY MONITORING METHODS

The use of supplementary methods is encouraged because they are low cost, easily carried out and directly applicable.

Generally, the resources required for such measurements for routine use is modest and can be incorporated into a 'common sense monitoring programme' to indicate how effective a control regime is. In addition, they can be used to give rapid feedback on the performance of controls, thus facilitating prompt remedial action.

They are:-

• spot measurement of workplace levels, e.g. by indicator tubes;

• measurement of releases ('sniffing') from specific items of plant, e.g. flanges, pump seals;

• measurement of or indicators of airflow, e.g. in local extract and general ventilation systems;

• detectors and alarms, e.g. in selected areas where releases are likely to occur. These methods are particularly effective for checking plant performance. For this reason they should be included in any monitoring programme whenever technically possible.


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3 EXPOSURE MEASUREMENT

Section 2 introduced exposure measurement as one of several methods for monitoring the adequacy and continuing effectiveness of exposure control measures. In this Section the focus turns to how exposure measurement is carried out and considers air measurement, biological monitoring, quality assurance and competence.

Acronyms used are explained in 3.6.

3.1 AIR MEASUREMENT

3.1.1 Selection of an appropriate sampling and analytical methodology Appropriate validated methods to meet the requirements of the overall exposure measurement strategy, and their subsequent analysis, should be selected. Methods for individual chemical substances are published by OSHA, NIOSH and the UK-HSE, i.e. the MDHS series (refer to Section 3.6 for an explanation of the acronyms).

It should be noted that publication of a method does not necessarily mean that it has been validated. The analysing laboratory must be satisfied on the validity before samples are collected.

3.1.2 Validation of sampling and analytical methods Critical steps in the validation of a method and guidance can be found in MDHS 27 & 54 as well as a number of NIOSH and OSHA documents.

More recently, CEN, the European Standard setting body, has issued a standard EN482 General Requirements for the Performance of Procedures for Workplace Measurements. This standard applies to all methods of measurement including direct reading devices. It will act as the basis of forthcoming European Standards for specific procedures and devices for workplace measurement, e.g. diffusive samplers, charcoal tubes, indicating tubes.

3.1.3 Records Records of exposure measurement details must be complete, traceable and stand up to close legal scrutiny. The record should consist of the survey report plus sampling and analytical results which is incorporated in the HRA process and associated record.

3.1.4 Types of exposure measurement survey A simplified overview of exposure measurement strategy is given in Appendix 3 which links the main measurement survey types in a flow chart and is applicable to measuring exposures to all agents hazardous to health. With regard to chemical agents, relevant action levels are given under item 2.5. Management of exposure measurement.

Further details on the three types of survey identified are outlined below. An overview of techniques used to obtain air measurement data is given in 3.1.5.

a) Preliminary Survey

The aim of the Preliminary Survey is to obtain quantitative exposure data of an acceptable quality and at reasonable cost to support the HRA decision-making process. It should be considered when:-

- there is doubt about compliance with a recognised OEL (see 1.1.4. above); - to determine Category I or Category II exposures (see 1.2.); - particularly serious effects could result from excessive exposure;

- justification is required for the implementation of control measures to meet acceptance criteria;

- the choice of control measures is dependent on concentration of exposure; - the efficiency of control measures needs to be evaluated; - to alleviate employee concerns; - legal requirements. It is appropriate to focus on workers who are expected to carry out tasks with the highest potential exposures, known as 'worst case' exposures. In this way possibly unnecessary measurement will be avoided, thereby enabling resources to be concentrated on improving exposure control measures.

b) Detailed Survey

If the degree and pattern of exposure cannot be reliably determined by the Preliminary Survey, a more thorough study will be necessary. The objective of the Detailed Survey is to obtain more accurate and reliable information about the exposures.

Results from the Detailed Survey would be expected to show if:-

- exposure is variable; - numbers of people are at risk from excessive exposure, e.g. operators and maintenance

personnel engaged in a plant turn-around; - personal sampling results are close to the relevant OEL. c) Routine Monitoring/Exposure Measurement

Routine exposure measurement may be required for the following reasons:-

- to comply with national legislation for particular agents/tasks/processes; - to verify compliance with OELs where exposure measurements are in Category II; - to confirm the continuing effectiveness of control measures and to give early warning

of changes in patterns of exposure before excessive exposures occur; - to obtain exposure data as part of an epidemiological study.

3.1.5 Personal exposure protocols Protocols may include:-

a) Personal Sampling

Sampling for personal exposures is designed to collect the air contaminant from the employee's breathing zone, normally over a full shift, for comparison with the relevant OEL. It may also be carried out for the duration of a particular task in order to identify the short term exposure peaks. The calculation for combining fractional exposures obtained over a shift for comparison with the time-weighted average OEL is given in Appendix 4.

There are two types of personal air sampling:-

• Dynamic (also known as active) sampling, in which the contaminant is collected by actively drawing the air through an absorbent or adsorbent material at a known flow rate by means of a small battery powered pump unit*. * If used in potentially flammable atmospheres, the pump unit should be certified as intrinsically safe.

• Diffusive (also known as passive) sampling. Diffusive samplers are compact devices (badge or tube) in which the contaminant diffuses through a membrane and is collected on a sorbent. They are most usually used to collect full shift samples.

Personal samplers also include direct readers for certain toxic gases such as H2S, CO and SO2.


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An important requirement of personal sampling is to ensure that a representative number of samples is obtained for groups of 10 or more individuals carrying out a similar work activity. The advice of an Occupational Hygienist should be sought when deciding on a representative number. Provided that the group is homogeneous* exposure data will be valid for the work activity. * A homogeneous group is a group of workers whose exposures are sufficiently similar that measuring the exposure of

any one worker in the group provides data which can be used to predict the exposures of the other workers in the same group.

Sampling is carried out to determine exposures which are representative of the whole process (particularly important in batch operations) and including 'normal' or 'worst case' conditions.

Repeat exposure measurements for any one worker may differ widely in view of the variable environmental factors at the workplace (e.g. air movement, position of operator in relation to contaminant source, fugitive emissions) and the way in which operations are carried out.

Part of the variation in exposure concentration is caused by sampling and analytical errors which can be estimated and minimised by method validation (see 3.1.2.).

b) Area Monitoring

Samples for area monitoring are collected from designated points around the workplace. The same sampling methods used for personal sampling may be applied to area monitoring (see 3.1.5.a.). In addition, where toxic substances are present, e.g. hydrogen sulphide, carbon monoxide, fixed multi-point sampling systems with direct reading instrumentation may be used to alert staff immediately to increases in workplace concentrations.

Although results of area monitoring do not relate directly to personal exposure they may be used to detect the pattern of emissions associated with process and workplace activities.

Area monitoring cannot be viewed as a substitute for personal sampling since actual breathing zone concentrations are heavily influenced by the work method.

c) Wipe samples

Although not a well developed technique, wipe samples may be used to estimate surface contamination, including skin, of chemical agents which have a low vapour pressure. Examples of contaminants for which wipe samples may be used are Pyrethroids and Polycyclic Aromatic Hydrocarbons (PCAs).

3.1.6 Interpretation of results (checking compliance) For practical purposes, a guide to compliance with an OEL or action level as per Category I or II (see 1.2.) is that not more than 1 in 20 samples of a homogeneous group, i.e. 5%, should exceed the prescribed limit. This equates with a 95% compliance level which is normally confirmed by the analysis of the data by probability (or cumulative frequency) plotting. This method depends on the data being log normally or near log-normally distributed and being representative of the full range of exposures. Refer to CONCAWE Report no. 87/57, see 3.5.1.

Alternatively, judgement on the need for additional measures to control exposures may be based on worst case exposure measurements, which, by definition, indicate the highest potential exposure.

3.2 BIOLOGICAL MONITORING

Biological monitoring involves the measurement and assessment of workplace agents or their metabolites (transformation products) in body fluids (usually urine or blood), or exhaled breath, to evaluate exposure and health risk compared to an appropriate reference.

Biological monitoring may be particularly useful because it reflects uptake by all routes, i.e. by skin absorption and ingestion as well as by inhalation where air measurement alone may provide insufficient information on possible uptake of chemical substances. Measurement of the 'internal dose' also provides information on personal hygienic behaviour, and the effectiveness of personal protective equipment and respirators.

Examples of biological monitoring methods are:-

− Lead in urine to evaluate exposure to Tetra Ethyl Lead and Tetra Methyl Lead (lead additives used in gasoline);

− S-Phenylmercapturic Acid (SPMA) in urine to evaluate exposure to benzene.

There is an increasing number of chemical agents or their metabolites for which guidelines for maximum allowable concentrations in body fluids have been recommended by authoritative bodies such as the American Conference of Governmental Industrial Hygienists (ACGIH) and the German MAK Committee.

Specific guidance on biological monitoring methods, sampling strategies and collection of samples in relation to a wide range of chemicals relevant to Shell is given in SIPM HSE Report 94.014: Laboratory Tests for Biological Monitoring and Biochemical Effect Monitoring.

3.3 QUALITY ASSURANCE

3.3.1 Good practice To demonstrate that the required standards for air sampling and analysis have been achieved an adequate quality assurance programme as outlined in, for example, MDHS 71 Analytical Quality in Workplace Air Monitoring should be followed. These elements are also applicable to a laboratory carrying out biological monitoring. The main elements of the programme are:-

a) Management of the Analytical Laboratory

Accreditation by an acknowledged scheme (e.g. NAMAS in the UK) will demonstrate that the laboratory's management and administration procedures are operating to a specified standard.

b) Internal quality control

This will indicate whether the analytical methodologies or techniques are routinely standardised and used correctly.

c) External quality control

This provides objective measurement of the analytical performance achieved by a laboratory and can give both the performance against a standard and a comparison against other laboratories. This can be achieved by participation in quality control schemes such as WASP, AQUA, RICE and PAT.

3.3.2 Managing critical quality control points Critical points exist in all measurement systems and must be identified and controlled for a laboratory to produce reliable results. In respect of the preparation of sampling packages and analysis of samples, the critical control points are:-

a) Selection of methods Liaison between persons collecting the samples in the field and analytical staff, confirmation of methods and sampling and analytical limits.

b) Preparation of Sampling Package


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Suitability of pumps, calibration, sampling media, certification of thermal desorption tubes where used, contamination-free specimen containers.

c) Transport and storage of samples Specified conditions of storage to ensure integrity of samples.

d) Sample Analysis Use of validated reference methods including calibration over the range, desorption or recovery efficiencies over the range, precision, accuracy, selectivity and quantifiable limits.

e) Inadvertent errors Systems to minimise errors due to, for example, the improper identification of a sample, failure to follow methods properly, data recording and transposing, calculating.

f) Analytical Instrumentation Equipment properly maintained and calibrated.

g) Analytical errors Quality assurance proficiency checks as a measure of performance.

3.4 COMPETENCE

Certain aspects of health risk assessment and exposure evaluation require relevant knowledge skills, experience and resources. Refer to the General Guide, Appendix 1, 'Competence', for an overview. Further advice can be obtained from Medical Advisers in the Service Companies.

3.5 FURTHER READING

Addresses for the organisations listed below are given in Appendix 7.

3.5.1 Air measurement • CONCAWE, Report no. 87/57 - Review of Strategies for the Evaluation of Employee

Exposures to Substances Hazardous to Health. 1987.

• CEN, PrEN137 - Assessment of Exposure to Chemical Agents in Air at the Workplace for Comparison with Limit Values and Measurement Strategy.

• BOHS, Technical Guide No. 11 - Sampling Strategies for Airborne Contaminants in the Workplace. 1993. ISBN - 0-948237-14-7. Published by H and H Scientific Consultants Ltd.

• UK-HSE, Guidance Note EH 42 - Monitoring Strategies for Toxic Substances. 1989. ISBN 0-11-885412-7.

• Monitoring for Health Hazards at Work, Indira Ashton and Frank S Gill. 2nd edition 1992. Publisher: Blackwell Scientific Publications, UK - ISBN 0-632-02984-6

• UK-HSE, MDHS 27: Protocol for Assessing the Performance of a Diffusive Sampler. 1987.

• UK-HSE, MDHS 54: Protocol for Assessing the Performance of a Pumped Sampler for Gases and Vapours. 1986.

3.5.2 Biological monitoring • HSE Report 94.014: Laboratory Tests for Biological Monitoring and Biochemical

Effect Monitoring, available from SIPM-HSE/51

• Industrial Chemical Exposure - Guidelines for Biological Monitoring. Robert R Lauwerys and Perrine Hoet. 2nd edition, 1993. Lewis Publishers.

• Biological Monitoring of Metals. C.-G. Elinder, L. Friber, T. Kjellström, G. Nordbery, G. Oberdoerster. International Programme of Chemical Safety (IPCS), WHO 1994.

• UK-HSE, EH 56 (January 1992) Biological Monitoring for Chemical Exposures in the Workplace.

• CEFIC Discussion paper on some practical aspects of the biological monitoring of exposure to genotoxic substances, March 1995.

3.5.3 Quality assurance • CEN 482 Workplace atmospheres - general requirements for the performance of

procedures for the measurement of chemical agents 1994

• UK-HSE MDHS 71: Analytical Quality in Workplace Air Monitoring. 1991.

3.6 ACRONYMS

ACGIH American Conference of Governmental Industrial Hygienists AQUA Analytical Quality Assurance Scheme (UK - HSE) BOHS British Occupational Hygiene Society CEN Comité Européen de Normalisation (European Union) CEFIC Conseil Européen de L'Industrie Chimique (European Council of

Chemical Manufacturers' Federations) CONCAWE The Oil Companies' European Organisation for Environmental and

Health Protection MDHS Methods for the Determination of Hazardous Substances (UK-HSE) NAMAS National Measurement Accreditation Service (UK) NIOSH National Institute of Occupational Safety and Health (USA) OSHA Occupational Safety and Health Administration (USA) PAT Proficiency Analytical Testing (NIOSH) RICE Regular Interlaboratory Counting Exchange (UK-HSE) UK-HSE Health and Safety Executive (UK) WASP Workplace Analysis Scheme for Proficiency (UK-HSE) WHO World Health Organisation


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APPENDIX 1 INTRODUCING TOXICOLOGY - AN OUTLINE

Toxicology studies the adverse effects that chemical substances have on living organisms. These adverse effects may occur as a result of local contact of the chemical with body surfaces, such as the skin and eyes, the respiratory system or the digestive tract, or may result from up-take into the body at sites remote from the place of up-take. The latter form is called systemic toxicity.

The local interaction between the chemical substance and a body surface may result in partial or complete disturbance of the physiological processes taking place in the cells of the surface linings. The outcome may be anything between a very light irritation (some swelling and redness) up to and including complete cell destruction as can be seen in serious (heat) burns.

Chemicals which are strong acids or strongly basic can cause these local adverse reactions, but lipophilic chemicals (such as solvents) may cause damage by dissolving the protective fatty layer of the skin.

Another toxic reaction following local contact may be the induction of skin or respiratory allergy. Fortunately, the number of chemicals which can cause allergic reactions (so called sensitisers) is limited.

Systemic toxicity may result from uptake/absorption/injection of chemical substances into the body. Usually the chemicals are transported in the blood and metabolised to make them less toxic and better and more rapidly excretable.

Sometimes, the metabolite(s) are more toxic than the parent compounds, whilst some chemicals are, even after being transformed in the metabolic process, only very slowly excreted, resulting in accumulation.

The systemic toxicity may be categorised in terms of the target organ(s) which is/(are) predominantly affected (kidneys: nephrotoxic; liver: hepatotoxic; bone marrow: myelotoxic, etc.), or in terms of the specific nature of adverse effects caused, such as carcinogenicity (the induction of tumours), mutagenicity (the induction of mutations) or teratogenicity (the induction of congenital malformations/dysfunctions).

The nature of the mechanistic processes which cause the adverse effects is usually very complex, but always based on interference with normal processes at the cellular level.

There are various defence and repair mechanisms which can deal with the invading chemicals. As these defensive mechanisms have limitations, they may be overcome. Chemicals of high toxicity require a lower dose to overcome the defence systems and cause adverse effects than chemicals of low toxicity, reflecting the differences in potency.

Central in toxicology is the relationship between the dose and the resulting effect (dose/effect relationship) and the relationship between the number of affected individuals which react with a specific effect in response to the dose (dose-response relationship).

Experimental toxicology seeks to clarify these dose-effect and dose-response relationships, in particular the NOAEL (No Observed Adverse Effect Level).

For risk characterisation it is necessary to identify the adverse effect of most concern, i.e. the Critical Effect, as this will be used to arrive at safe levels of exposure.

Experimental toxicology tests are standardised by OECD guidelines and range from a very simple determination of the lethal dose for 50% of the animals (LD 50) to very sophisticated long term investigations of all possible adverse effects and the underlying causative mechanisms.

new and existing substances and how the results are 'translated' into Materials Safety Data Sheets and Labels. Footnote

EU Commission Regulation 1488/94 on Risk Assessment of Existing Substances: Terminology of Risk

Risk Assessment A generic term describing an administrative and technical process which entails some or all of he elements below.

Effects Assessment: - i) Hazard identification

Identification of the adverse effects which a substance has an inherent capacity to cause; and, where possible and/or appropriate, the assessment of a particular effect.

ii) Dose-response assessment Estimation of the relationship between dose (or level of exposure) and the incidence and severity of an effect.

Exposure Assessment Determination of the pathways and rates of movement of a substance, its transformation or degradation and its concentration. when possible, at critical points in order to estimate the doses to which defined populations, environmental compartments or specific ecosystems are actually exposed.

Risk Characterisation Estimation of the incidence and severity of the adverse effects likely to occur in a population, environmental compartment or ecosystem exposed to a substance and may include: -

Risk Estimation Quantification of the likelihood of the incidence and severity of the adverse effects.

Risk Reduction The taking of measures to reduce the likelihood of adverse effects occurring.


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APPENDIX 2 COMMON TOXICITY TERMS

Toxicity This is defined as 'the ability of a chemical compound to produce injury once it reaches a susceptible site in or on the body'.

Toxic substance An agent which if inhaled, ingested or absorbed through the skin, may result in/produce/involve serious, acute or chronic health effects and even death.

Acute health effect This effect occurs suddenly and in a short time (seconds to hours) following exposure, generally to higher levels or concentrations of a health hazard. An acute exposure runs a comparatively short course. Examples are:-

- inhalation of hydrogen sulphide gas leading to respiratory paralysis;

- inhalation of cadmium fume from silver solder leading to pulmonary oedema (fluid on the lungs);

- inhalation of solvents leading to narcotic effects and coma.

Chronic health effect This effect occurs gradually over a long period of time following repeated exposure to relatively low levels or concentrations of a hazardous agent, e.g. carcinogenic agents. In certain cases, short term exposure may result in a delayed effect which may remain for a long time.

Acute and chronic Some chemical agents may have both acute and chronic health effects, e.g. exposure to short term high levels of benzene will result in acute narcotic effects, whilst exposure to repeated relatively low levels may result in damage to the red blood cells and potentially lead to the development of myeloid leukaemia, cancer of the blood.

Additive effect This applies to mixtures which contain chemical agents that act on the same body organ(s), or by similar mechanisms, so that the effects support each other and the agents are additive in their effect. (See also 'synergistic effect')

Asphyxiant (simple) A chemically inert gas which can replace the oxygen content in air in confined spaces thereby causing suffocation, e.g. nitrogen, argon, propane, butane, carbon dioxide.

Asphyxiant (chemical) A chemical that interferes with the take up and use of oxygen in body tissues, e.g. carbon monoxide, hydrogen sulphide, hydrogen cyanide.

Cancer An autonomous growth of cells leading to tumours. Tumours may be benign in which case they do not spread to other sites. They may be malignant in which case they tend to spread locally or to other sites and to recur when removed.

Carcinogen Induces malignant tumours in tissue, e.g. asbestos, hardwood dusts, arsenic, benzene.

Corrosive Destroys or damages (burns) living tissue on contact. At particular risk are the skin and eyes. If a corrosive is inhaled as a mist or vapour the irritation to the lining of the lungs may result in the lungs filling up with fluid (pulmonary oedema) which can be life threatening, e.g. mists from concentrated solutions of strong acids such as sulphuric acid, or alkalis such as caustic soda.

Dermatitis Dermatitis is usually caused by chronic exposure to agents which remove the skin's natural oils causing it to become dry and lose its elasticity. Types of dermatitis are:-

- contact dermatitis: reddening, fissuring and crusting;

- folliculitis (oil-acne) due to blockage of hair follicles with consequent obstruction and inflammation;

- hyperkeratosis with warts or papilloma which may become malignant.

Genotoxic carcinogen An agent capable of damaging the DNA in cells (see mutagen)

Irritant Produces local inflammation of the skin, eyes, nose or lung tissue. Prolonged or repeated exposure of the skin to an irritant may lead to contact dermatitis. Examples of irritants are lime, fibreglass, ammonia, sulphur dioxide, chlorine.

Local effect This means that any toxic effect takes place at the point or area of contact. (See also 'Systemic effect').

Malignant Refer to 'cancer'.

Mutagen/mutation Mutagens can damage the DNA in a cell which may lead to a mutation, i.e. a permanent change of the properties of a cell. Cancers caused by genotoxic chemicals are believed to be started by damage to DNA. These chemicals are termed mutagens and must be treated with caution, e.g. ethylene oxide.

Narcotic Induces dizziness, nausea and coma, e.g. organic solvents such as alcohols, esters, ethers; hydrocarbon mixtures such as gasoline.

Relative vapour density The relative vapour density is the weight of a specific volume of a gaseous chemical agent compared to the weight of the same volume of air.

If the relative vapour density of a pure gas is less than 1 the gas will rise and collect at ceiling level (if indoors) or disperse into the atmosphere (if outdoors).

Reproductive toxicity May affect male or female fertility and/or cause non-heritable birth defects in off-spring, e.g. certain low molecular weight glycol ethers.

Pneumoconioses Generic term for lung diseases caused by some respirable dusts such as crystalline quartz (silicosis) and asbestos (asbestosis) where scar tissue (fibrosis) has resulted in a loss of lung function.

Sensitiser Causes an allergic reaction. This may include wheezing and shortness of breath (asthma) for lung sensitisers, or a


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rash leading to allergic dermatitis for skin sensitisers, e.g. isocyanates (lung), nickel metal (skin), epoxy resins (skin).

Synergistic effect This applies to mixtures which contain chemical agents that act on the same organs, or by similar mechanisms, so that the overall effect is considerably greater than the sum of the individual effects, e.g. smoking and exposure to asbestos fibres significantly increases the risk of contracting lung cancer. (See also 'Additive effect').

Systemic effect In this case the site of toxic effect is other than the point of contact and pre-supposes that absorption has taken place (See also 'Systemic toxicity')

Systemic toxicity A generic term used to describe agents toxic to one or more specific target organ(s) or body system(s). (See also 'Systemic effect').

APPENDIX 3 OVERVIEW OF EXPOSURE MEASUREMENT STRATEGY


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APPENDIX 4 CALCULATION FOR COMBINING FRACTIONAL EXPOSURE MEASUREMENTS TO ALLOW COMPARISON WITH A SPECIFIED REFERENCE PERIOD

1 UNITS OF MEASUREMENT

1.1 Gases and Vapours Two units are used to express the concentration of gases or vapours, viz.:-

• parts per million (ppm), a measure of concentration by volume; or

• milligrams per cubic metre of air (mg/m3), a measure of concentration by mass. The inter-conversion formulae are:-

a) to convert mg/m3 to ppm:- ppm = mg/m3 x 24.5 / Molecular Weight of chemical

b) to convert ppm to mg/m3:- mg/m3 = ppm x Molecular Weight / 24.5

Both formulae assume Normal Temperature and Pressure, i.e. 25°C and 760 mm of Mercury (1 bar).

1.2 Particulates Airborne concentrations are usually expressed in mg/m3 as the 'Inhalable Fraction' or 'Respirable Fraction'.

Airborne concentrations of fibrous materials, e.g. Asbestos and Man Made Mineral Fibres (MMMF) can be expressed either as mg/m3 or as fibres per millilitre of air (f/ml).

2 CALCULATIONS

2.1 Time Weighted Average 8-Hour Reference Periods In order to compare exposure measurements with the appropriate 'Time Weighted Average 8-hour reference period' it is necessary to express the total exposure in any 24-hour period as a single equivalent uniform exposure for 8 hours. This is represented mathematically by:-

C1T1+ C2T1 + ........ + CnTn / 8 hours

Where 'C' is the occupational exposure and 'T' is the associated time in hours in any 24 hour period.

In the example given below the working shift has been taken as 8 hours.

Example:- A maintenance technician is servicing the in-line blending equipment for mixing tetramethyl lead into the gasoline blend stock. The work was scheduled for the whole day but breaks were taken for coffee/tea, lunch etc.

The work periods, sampling duration and exposure levels were:- Working period Sampling duration (h) Exposure mg/m3

0800 - 1030 2.5 0.25

1030 - 1045 0.25 0

1045 - 1245 2.0 0.05

1245 - 1330 0.75 0

1330 - 1530 2.0 0.3

1530 - 1545 0.25 0

1545 - 1715 1.5 0.25

The 8 hour TWA is therefore:-

The OEL, as recommended by the ACGIH, for tetramethyl lead is 0.15 mg/m3.

The result is 1.5 x OEL which equates with an Exposure Rating of D. With a Hazard Rating of 4 for alkyl lead compounds risk reduction measures must be applied. In the short term it could be reasonably practicable to use respiratory and skin protection. If this were not acceptable in the longer term, e.g. in the case of a frequent task, plans to implement risk reduction measures by engineering means which control alkyl lead at source would need to be introduced.

2.2 Short Term Reference Period In order to check compliance with a STEL, exposure should be recorded as the average over the specified short-term reference period and should normally be determined by sampling over that period. For example:-

• where the exposure period is less than 10 minutes the sampling result should be averaged over 10 minutes. For example, if a 5-minute sample produces a level of 500 ppm and is immediately followed by a period of zero exposure then the 10-minute average exposure will be 250 ppm;

• where the exposure period is 10 minutes or longer measurements can be restricted to 10 minutes and evaluated by reference to the STEL.

• where data are required to evaluate risk in a specific task, the full duration of the task should be sampled.


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APPENDIX 5 ADDRESS LIST

ACGIH: Kemper Woods Centre, 1330 Kemper Meadow Drive, Cincinnati, OH 45240

BOHS: Suite 2, Georgian House, Great Northern Road, Derby, England, DE1 1LT

CONCAWE: Madouplein 1, B-1030, Brussels, Belgium

CEFIC: Avenue E. Van Nieuwenhuyse 4 - Box 1, B-1160 Brussels, Belgium

CEN : Rue de Stassart 36, B-1050, Brussels, Belgium

UK-HSE: HSE Books, PO Box 1999, Sudbury, Suffolk, England, CO10 6FS

NIOSH: US Government Printing Office, Superintendent of documents, Washington, DC 20402, USA

OSHA: 200 Constitution Avenue, N.W. Washington, DC 20210, USA

WHO: 1211 Geneva 27, Switzerland

chemical hazards, health risk assessment and exposure evaluation

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