3 hazard control

3 HAZARD CONTROL

E. R. Vaidogas, Lectures on OSH 2

The hazard of sharks … 1/6

Sharks are a dormant hazard

Figures in the slides 2…6 retrieved from http://www.safework.sa.gov.au/



Potential or “armed” hazard



Eliminating hazard

Replace “sharks” with “toys”



Introducing administrative tools

May be you will have time to escape …



Engineering out the problem

Encage yourself!



Provision of personal protective equipment

An armoured holiday


Hazard control in the risk analysis

Activity

Hazards

Accident

Likelihood of accidents Outcome (Losses)

Preventing or reducing likelihood of

accidents

Minimising and controlling damage

Where we are?


Methods to control hazards

Two groups of options

Accident prevention Minimising and controlling damage

1. Eliminating hazards

2. Limiting hazard levels

3. Isolation, barriers, and interlocks

4. Fail-safe designs

5. Minimising failures

1. Isolation and barriers

6. Minor loss acceptance

2. Personal protective equipment

4. Escape & survival equipment andprocedures

5. Rescue equipment and procedures6. Warning means and devices

7. Safe procedures

The option with the lowest number is highly desirable

8. Backout and recovery

3. Weak links


Accident preventionA

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Control of hazards by design

Control of hazards by procedural means

Reliability-oriented methods

Intrinsically safe methods

1. Eliminating hazards

2. Limiting hazard levels

4. Fail-safe designs

5. Minimising failures

6. Warning means and devices

7. Safe procedures

8. Backout and recovery

3. Isolation, barriers, and interlocks


1. Eliminating hazards 1/4A

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General

The following general features of hazard control should be observed:

1. Designs to eliminate hazards are most preferred over any other method.

2. Where safeguards by design are not feasible, protective safety devices should be employed.

3. Where neither design nor safety devices are practical, automatic warning devices should be incorporated.

4. Where none of the above is feasible, escape procedures and personnel training should be used.



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Intrinsic safety

The most effective method of avoiding accidents is with designs that are “intrinsically safe”. Intrinsic safety can be achieved by either two methods:

1. Eliminating the hazard entirely.2. Limiting the hazard to a level below which it can do no harm.



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Complete elimination: good housekeeping

Tripping over misplaced objects, slipping on wet or oily surfaces,

and spontaneous ignition of trash or oily rags can be eliminated

simply by keeping facilities clean and orderly.



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Complete elimination: examples

1. Using non-combustible instead of combustible materials. This method has been observed with paints, fabrics, hydraulic fluids, solvents, and electrical insulation.

2. Using pneumatic or hydraulic, instead of electric, systems where there is a possibility of fire or excessive heating. Fluid control systems are often applied for this reason.

3. Rounding edges and corners on equipment so personnel will not injure themselves.

4. Eliminating leaks using continuous lines with as few connections as possible.


2. Limiting hazard level 1/2A

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Hazard level limitation

In certain instances the type of hazard can not itself be eliminated.

However, the level of the hazard might be limited so no injury or damage will result.

Electricity under some circumstance can be fatal.

It may be possible to eliminate any adverse effects by using low-voltage, low temperature power, such as 12-volt power or battery power.


2. Limiting hazard level 2/2A

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Hazard level limitation: examples

1. Providing overflow arrangements that will prevent liquid levels from getting too high.

2. Using solid state electrical devices where flammable or explosive gases may be present, so any power requirements will be far less than required for ignition of a flammable mixture.

3. Ensuring that the concentration of a flammable or toxic gas is far less than a dangerous limit. If the limit is exceeded, a blower could be started automatically or inert gas introduced.

4. Adding diluters to air where flammable dusts are present to minimize the possibility of an explosion.

5. Incorporating automatic relief provisions to keep pressure within a safe limit.

6. Using grounds on capacitor or capacitive circuits to reduce charge accumulations to acceptable levels after power is shut off. This will lessen the tendency for an electric shock.


3. Isolating hazards 1/4A

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General

Isolation here = separation employed as an accident prevention measure.

Fire requires the presence of a fuel, oxidiser, and ignition source. Isolating any one of these from the other two will eliminate any possibility of fire.

Some grades of bituminous coal are often stored underwater, isolating the coal from the oxygen and ignition source needed for fires to start

spontaneously.



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Isolation: examples

1. Isolating workers inside protective garments or equipment to prevent environmental injuries.

2. Use of thermal insulation to prevent persons from contacting hot surfaces which can burn them.

3. Use of isolators to keep noise inside closed spaces.

4. Use of “explosion-proof” or encapsulated electrical equipment in flammable atmospheres.

5. Keeping corrosive gases and liquids from incompatible metals or other materials that might be affected adversely.



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Lockins & lockouts

Lockout: prevents an event form occurring or prevents a person, object, force, or other factor from entering an undesired zone. Lockin: keeps a person, object force, process, or other factor form leaving a restricted zone.

Lockout example: a switch closing electrical circuit secured with a lock that only specific persons can open. Lockin example: the same switch with lock preventing opening of the circuit.


3. Isolating hazards 4/4 A

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Interlocks

Interlocks initiate/prevent action or motion; other send signals to other devices which initiate/prevent the action or motion:

Parameter sensing: presence, absence, excess, or inadequacy of pressure, temperature, flow or other parameter permits or stops action.

Timers and time delays: operation of the equipment can take place only after a specific length of time has passed.

Photoelectric devices: interruption or presence of light on a photoelectrical cell generates a signal which can stop or initiate action.


4. Fail-safe designsA

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Equipment failures yield a high percentage of accidents

Since failures will occur, fail-safe arrangements are often made to prevent injury to personnel, major catastrophes, damage to equipment, or degraded operations:

Fail-passive arrangements: circuit breakers and fuses for protection of electrical devices which deenergise system in case of overload.

Fail-active arrangements: a battery operated smoke detector maintains energised state of the system but activates eliminating the possibility of accident (sprinklers, say).

Fail-operational arrangement: allows system functions to continue safely until corrective action is possible.


5. Failure minimizationA

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Reducing critical failures causing accidents

Safety factors and margins: over-design of the system.

Failure rate reduction: increase expected lifetimes.

Parameter monitoring: keep under surveillance specific parameters, say, temperature, noise, gas concentration.


6. Warning means and devices 1/3A

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Avoiding accidents by attracting attention

Illumination A hazardous area brightly illuminated than non-hazardous surrounding areas

Having well-lit highway intersections, obstacles, stairs, and transformer substations

Discrimina-tion

Paint a physical hazard in a bright colour or in alternating light and dark colours

A structure, piece of equipment, or fixed object which could be hit by a moving vehicle is painted yellow or orange

Notes in instructions

Warning and caution notes inserted in operations and maintenance instructions and manuals to alert personnel to hazards

A warning in a car owner’s manual to block the wheels before jacking the car to change a tire

Visual sense



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Alarms A siren, whistle, or similar sound device provides warning of existing or impending danger

A siren indicates that there is a fire in a plant; a siren or whistle warns personnel to clear an area where blasting is to take place

Buzzer Alerts person that a specified time has passed or that time has arrived to take the next step in a sequence of actions

Some compressed air packs contain buzzers that sound when the pressure in the tank has decreased to a predetermined level, or after a preset time has passed

Shout Voice action to warn of a danger One person warns another of an obstruction

Auditory sense



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Odour detection

Presence of an odorous gas can indicate the presence of a hazard

An odorant is added to refined natural gas (which has no odour) so that leaks can be readily detected

Burning materials give off characteristic odours

The presence of an unseen fire can sometimes be detected by characteristic odours of products of combustion

Overheating equipment can be recognised by the odour generated

Vaporisation of oil can permit detection of a hot bearing; odour of hot, streaming water can warn a car driver of a broken radiator hose

Smell


7. Safe proceduresA

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“when all else fails, read the instructions”

The need to follow prescribed procedures.

Safe procedures should include any warnings about hazards established by the analysis of the system.

Unfortunately, since many people to not read operating procedures until they have run into difficulty (“when all else fails, read the instructions”),

and ignore warnings, this method has low priority in rating means of preventing accidents.


8. Backout & recoveryA

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“A near-miss”

A failure, error, or other adverse condition may eventually develop into a mishap. At this time, a contingency or emergency may then exist.

By suitable action an accident can be avoided from this abnormal situation, which may be an extremely dangerous one.

Failure to act correctly or adequately can permit the situation to deteriorate into a mishap.

This interim period extends from the time the abnormality appears until normality is recovered or accident develops.

If recovery takes place, the incident can be considered a near-miss.


Minimising and controlling damageD

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1. Isolation and barriers

6. Minor loss acceptance

2. Personal protective equipment

4. Escape & survival equipment and procedures

3. Weak links

Designmeans

5. Rescue equipment and proceduresProcedural

means


1. Isolation and barriers 1/2D

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Distance by sitting possible points of accidents far from persons, equipment, or vulnerable structures.

Deflectors can be used to lessen damage by deflecting or absorbing energy. The reminder should then constitute less than the amount that would be damaging (heat reflectors from fires, noise shields, or sloped barricades between explosive storage buildings)

Containment to prevent the spread of fire such as sprinkler systems.

Barriers of metal, concrete blocks, or other impenetrable or nonconductive material.

Physical insulation


1. Isolation and barriers 2/2D

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The tank’s protective barrier in gas station


2. Personal protective equipment 1/3D

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1. For scheduled hazardous operation: spray painting would require protective clothing during scheduled operations.

2. For investigative and corrective purposes: it may be necessary to determine if the environment is dangerous because of a leak, contamination, or other condition.

3. Against accidents: this may be constitute the severest requirements because the first few minutes after an accident takes place may be the most critical.*

* Reaction time to suppress or control any injury or damage is extremely important. Because of this, protective equipment must be simple and easy to don and operate, especially because it is often required at a time of stress.

Categories



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The hazard of entering a tank: scheduled/investigative operation



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Protection in case of accident: accidental release of toxic material


3. Weak links 1/2D

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Boilers with mechanical fuses that melt when water levels drop excessively so steam can escape so there is no rupture.

Sprinklers that open to release water for fire extinguishing.

Drop-off panels that will fail along designed fault lines to provide openings to energy of an explosion.

“Weak link” = component designed to fail at low level of stress

The most common example is electrical fuse


3. Weak links 2/2D

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Ronan Point Explosion: fatal structural collapse, UK 1968

Floor 18, Apartment 90

Only a few weeks after the occupants had moved in, a gas explosion demolished a load bearing wall, causing the collapse of one entire corner of the building. Four people were

killed in the collapse, and seventeen were injured.


4. Escape and survival equipment 1/2D

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Abandoning or scarifying structures, vehicles, or equipmentto avoid injury and to personnel

Easy escape and survival Escape and survival might be problematic

Fire in a multi-storey plantFire in a single-storey plant


4. Escape and survival equipment 2/2D

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Telescopic Poles in Aluminium/Carbon Fibre


5. Rescue procedures and equipmentD

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Persons involved in an accident and not able to escape

1. Fellow workers familiar with the plant, hazards, equipment, and who may have been advised of what to do in any emergency.

2. Untrained persons unfamiliar with equipment (passers-by, say).

3. Persons knowledgeable and capable of handling the need.

A rescuer can be everyone:


6. Minor loss acceptanceD

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The decision to accept losses of potential accidents can be based on the results of a quantitative risk assessment.

Event

eConsequencOucome

Time

EventLikelihood

Time

eConsequencRisk


To end of part three

1. What are the methods of accident prevention? List at least one example of application of each method.

2. How can the magnitudes of hazards be limited? Describe how a design can be intrinsically safe.

3. How can isolation be used to keep personnel from accidents?

4. What is meant by keeping equipment fail-safe? How can it be done?

5. How are monitors used to prevent accidents? Give three applications. List the characteristics a good monitor should have.

6. What is the buddy system and how is it used? What are the two types of the buddy system?

7. Tell how the human senses can be used as monitoring and warning devices ad give some examples of each.

8. What are back-out and recovery as they apply to accident prevention?

9. List the methods by which injury and damage can be minimised in the event of an accident.

10. What is the “weak link”? Describe some common types.

11. Describe the relations between escape, survival, and rescue. Tell how equipment designs and procedures can be developed for them.

Examination questions

3 hazard control

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