nagarjuna fertilizers & chemicals ltd.,
TRANSCRIPT
NAGARJUNA FERTILIZERS & CHEMICALS LTD., KAKINADA
RISK ANALYSIS REPORT OF
CUSTOMISED FERTILIZER GRANULATION PLANT
RAMS SAFETY CONSULTANTS 4/1, Parsn Reveira,
4TH Main Road Extension Kottur Gardens,
Chennai - 600 085 Phone : (044) 2447 1166
Mobile- 98400 78043 E.mail [email protected] : [email protected]
CONTENTS SL.NO. TITLE PAGE NO
Preface
i
Profile of Rams Safety Consultants
ii
Profile of the Specialists
iii
Executive Summary
Vi
1.0
NFCL Profile
1 - 1
2.0
Scope, Objective and Methodology
2-1
3.0
Data For Risk Assessment
3 - 1
4.0
Maximum Credible Accident Scenarios
4 - 1
5.0
Consequence Analysis
5 - 1
6.0
Failure Probability
6 - 1
7.0
Risk of Auto Ignition, Risk of Chemicals Under Production, Handling, Storage and Transportation, Risk due to Electrical Short Circuiting or any Other Source, Threats from the Existing Plants
7 - 1
8.0
Conclusion & Recommendations
8-1
PROCESS SAFETY
TRAINING
ii
PROFILE OF RAMS SAFETY CONSULTANTS
Started in 1985, Rams Safety Consultants (RSC) is one of the earliest safety
consultancy firms established in India to meet the specific demands of the industries in
the area of safety services. RSC consists of a group of dedicated professionals having
vast industrial experience with specialized knowledge in their respective fields.
RSC has successfully carried out more than 300 Safety Audits, 70 Risk/Consequence
Analysis Studies, 70 Hazop Studies and a number of Process Safety Training
Pogrammes all over India.
Services provided by RSC
RISK ANALYSIS/QRA
RSC HAZOP STUDY
SAFETY AUDIT
INSPECTION
ELECTRICAL SAFETY AUDIT
PREPARATION OF EMERGENCY PLANS
OHSAS 18001 &
ISO 14001 Systems
Implementation
iii PROFILE OF THE SPECIALISTS
1. SHRI.R. RAMADORAI Qualifications: B.E. (Chemical) Work Experience: Eight years of process experience followed by
18 years as Head of the Department of Safety and Fire in Fertilizer Corporation of India (FCI) Ltd.
Since 1984, working as freelance safety consultant and also heading Rams Safety Consultants. He has carried out Safety Audits, HAZOP Studies and Risk Analysis for a large number of industries all over India. He has conducted a number of safety training programmes all over India in chemical, petrochemical and fertilizer industries. He had been to Turkey as UNIDO Safety Expert. He has presented a number of papers in India and abroad.
He was a member of State Level Safety Task Force / Expert Committee of Government of Tamilnadu.
He was nominated as Member of Board of
Governors of National Safety Council to represent Public Sector Undertakings
iv
2. SHRI. P.V. RAGHAVAN Qualification: B Sc (Chem)
Work Experience: Over 30 years of experience in the commissioning and operation of the following plants in the fertilizer industry:
1. Air Separation 2. Water Treatment 3. Ammonia Was formerly a Chief Engineer in the Fertilizer Corporation of India. He is with Rams Safety Consultants for the last 18 years and during this period has carried out a number of Safety Audits, Hazop, and Risk Analysis Studies.
v
EXECUTIVE SUMMARY
Nagarjuna Fertilisers & Chemicals Limited (NFCL) is located in Kakinada, East
Godavari District of Andhra Pradesh. The NFCL complex consists of two ammonia
and two urea plants. The ammonia plants are based on Haldor Topsoe Technology
and urea plants on Snamprogetti, total recycle with ammonia stripping. The feed
stock of plant I is natural gas. and plant II, which was on mixed fuel (60 % naphtha
and 40 % natural gas), has been switched over to natural gas. The shortage of CO2,
is made up from a 450 MTPD Carbon Di Oxide Recovery Plant from the flue gases
of Ammonia Plant I Primary Reformer stack. The production capacity of each stream
of ammonia plant-I & II is 1325 MTPD & 1300 MTPD and urea-I & II is 2325 MTPD
& 2280 MTPD. Other associated offsite and utility plants are available. NFCL is setting up a 400 MTPD capacity Customized Fertilizer Granulation (CFG) Plant. This plant would be put up inside the existing complex. NFCL desired to carry
out Risk Assessment Study of the proposed customized fertilizer granulation plant to
cover risk of auto ignition, risk of chemicals under production, handling, storage and
transportation, risk due to electrical short circuiting or any other source, threats from
the existing plants, and the consequence analysis of the NG line to the plant
mentioned above, among other things.. .Rams Safety Consultants (RSC) of Chennai
was assigned the job.
Results of the analysis
Risk of Chemicals Under Production, Handling, Storage and Transportation
The materials stored, handled and mixed is thermally stable at normal working
conditions during storage and transport. The materials do not have the
tendency for auto ignition based on their chemical characteristics. They will
not get ignited due to normal ignition sources and heated metals. So there is
no possibility of fire taking place in the storage area due to auto ignition, hot
work etc., and leading to emission of toxic gases from the stored materials.
vi
The available literature does not mention about any evolution of toxic gases to
that extent that it needs dispersion/consequence modeling.
Use of recommended PPE in handling these materials would go a long way in
minimizing handling accidents.
Risk Due To Electrical Short Circuiting
Short circuits occur mainly due to overloading as it leads to heating effect and
may result in fire breakout and fatal accidents, if proper instructions are not
followed. Such incidents can be minimized to a great extent if adequate fire
precautions are observed. Electrical fires spread rapidly and cause loss of
lives and property.
Threats from the Existing Plants
The CFG Plant is to the west of existing cooling tower of ammonia plant II and
north west of urea plant II cooling towers. Any release of chlorine from the
cooling towers might affect the personnel in this plant subject to the direction
of the wind.
Similarly any major ammonia release from ammonia and / or urea plants
might have an effect on the personnel working in CFG Plant, again, subject to
wind direction.
vii
Guillotine Failure of the NG Line to HAG Burner
The Jet fire ellipse radiation levels and the furthest distance of flash fire would
be confined to the factory premises.
Sl. No
Scenario Wind Velocity / Stability
Damage Distance (m) Radiation Level Jet Fire Ellipse
Flash Fire Envelope
37.5 kW / m2
12.5 kW / m2
4 kW / m2
Furthest Extent 21716.9 ppm
Furthest Extent 43433.9 ppm
1
2” NG line to HAG rupture
3 B 9.94 10.50 11.85 7.81 5.17
3 D 10.26 10.68 12.0 7.84 5.15
5D Not Reached
10.78 12.26 6.56 4.70
Specific Recommendations Special attention in terms of inspection and safety management systems for
NG line is suggested.
Hydrocarbon detectors may be suitably located in critical areas with means of
prompt isolation.
Electrical Short Circuiting
The recommendations made below, if followed might obliterate fires and
consequent damages due to electrical short circuit
The lighting fixtures in the NG routing and HAG area should conform to the
standards suitable for service in that area and once installed must be
maintained.
Use only ISI certified appliances.
viii
Use good quality fuses of correct rating, miniature circuit breakers and earth
leakage circuit breakers.
Use one socket for one appliance.
Switch off the electric supply of the fire affected areas.
Fuses and switches should be mounted on metallic cubicles for greater safety
against fire.
Replace broken plugs and switches.
Keep the electrical wires away from hot and wet surface.
Don’t use substandard fixtures, appliances.
Never have temporary or naked joints on wiring.
Don’t lay wires under carpets, mats or doorways. They get crushed, resulting
in short circuiting.
Don’t lay wires under carpets, mats or doorways. They get crushed, resulting
in short circuiting.
Don’t allow appliances cords to dangle.
Don’t place bare wire ends in a socket.
No combustible material should be permitted to be stored in the plant
ix
Threats from the Existing Plants With the current predictive and preventive maintenance practices and testing
and calibrating procedures, the possibility of major release of hazardous
chemicals from the existing unit appears to be very remote.
Mock drills should be conducted posting observers. Pamphlets may be issued
to all the employees detailing how to respond in case of an emergency.
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1.0 NAGARJUNA FERTILISERS & CHEMICALS LIMITED - PROFILE
1.1 Location
Nagarjuna Fertilizers & Chemicals Limited (NFCL) is located at Kakinada,
East Godavari District of Andhra Pradesh. The total area covered by the
NFCL plant is about 380 acres. It is situated about 500 meters from the
coast just next to Kakinada bay. The site is about 2.5 m above mean sea
level. It is surrounded on the north by Coromandel Fertilizers Limited, Bay
of Bengal on the East, Kakinada town on the west and green belt on the
south. The width of the green belt is 1 km wide and it also extends on the
west. Incidentally the green belt is between the plant and the town. The
site plan is enclosed as Figure 2.1 1.2 The Fertilizer Complex
The NFCL complex consists of two ammonia and two urea plants. The
ammonia plants are based on Haldor Topsoe Technology and urea plants
on Snamprogetti, total recycle with ammonia stripping. The feed stock I is
natural gas. To make up CO2 short fall due change over from naphtha +
NG to NG, a 450 MTPD Carbon Di Oxide Recovery Plant from the flue
gases of Ammonia Plant I Primary Reformer has been put up. The
production capacity of ammonia plant-1 is 1325 MTPD, ammonia-2 is
1300 MTPD, while Urea-1 & 2 is 2325 MTPD & 2280 MTPD respectively.
Other associated offsite and utility plants are available. NFCL is going in for a Customised Fertilizer Granulation (CFG) Plant of
400 MTPD production capacity. This plant would be put up inside the
existing complex.
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1.3 Brief Process Description of CFG Plant The main sections of the plant are:
• Raw material receiving
• Raw material feeding
• Process section
• Finished product bagging & Conveying
• Pollution control
All the required Solid raw materials (DAP, Urea, MOP, Ammonium
Sulphate, Filler like dolomite or clay ) & Micro Nutrients (Zinc, Boron,
Iron, Sulphur etc ) from the storage bins are proportionately pre
weighed on weigh feeders and fed to the crushers followed by paddle
mixer. This premixed product is fed into the rotating granulator where
steam and water are added to provide sufficient liquid phase by causing
the dry raw materials to agglomerate further into product size granules.
These moist granules are fed into a rotary dryer where they are dried by
hot air generated which the air is drawn from blower in Hot Air
Generator with natural gas firing. These hot granules are cooled in a
rotary cooler and fed to the rotary screen and the oversize material is
separated, crushed & recycled back to the granulator along with
scrubber solution and undersize fraction. The desired product size
material is sent for bagging after coating and addition of Zinc using anti
caking agent. The product is bagged in 50Kg bags by automatic
Weighing and bagging machines (2Nos. 500 Bags/Hr each) and
stitching machines (2Nos) is then dispatched through road.
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The plant is incorporated with stack of 40 meters in height and other
pollution control devices to take care of environmental aspects. The
exhaust air from various equipment is sent to de-dusting and the clean
air is vented to atmosphere through a stack. The de-dusting system
comprises of cyclones followed by water scrubbers and the material
laden liquid is recycled to meet the requirement in granulator.
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2.0 SCOPE, OBJECTIVE & METHODOLOGY
2.1.0 Scope
The scope of work as per NFCL Service Work Order No. 1200004449 dated 12.01.2011 is to carry out, among other things, Risk Assessment Study of the proposed customised fertilizer granulation plant to cover risk of auto ignition, risk of chemicals under production, handling, storage and transportation, risk due to electrical short circuiting or any other source, threats from the existing plants, Hazop Study of steam, utility and NG line and the consequence analysis of the NG line to the Hot Air Generator of the plant mentioned above.
2.2.0 Objective
2.2.1 The objective of this study is to carry out consequence analysis for the line rupture scenario of the NG line to the Hot Air Generator, risk of auto ignition, risk of chemicals under production, handling, storage and transportation, risk due to electrical short circuiting or any other source, threats from the existing plants, Hazop Study of steam, utility and suggest measures for risk reduction so as to bring the risk to as low as reasonably practicable.
2.1.2 Risk arises from hazards. Risk is defined as the product of severity of consequence and likelihood of occurrence. Risk may be to people, environment, assets or business reputation. This study is specifically concerned with risk of serious injury or fatality to people.
2.1.3 The following steps are involved in the analysis: • Study of the plant facilities and systems. • Identification of the hazards. • Enumeration of the failure incidents. • Estimation of the consequences for the selected failure incidents.
The process of quantitative risk assessment (QRA) is shown in the following block diagram.
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2.3.0 Consequence Calculation Procedure
2.3.1 The first step in risk assessment is selection of failure scenarios involving release of hazardous material from process units or storage tanks. The failure scenario considered in CFG Plant is the line rupture of NG line to the Hot Air Generator.
2.3.2 The next step in Risk Assessment is to analyze the consequences of accidental releases of toxic/ flammable material from piping, plant equipment or storage tanks, such as characteristics of the cloud formed and distances to which the adverse effects may reach.
2.3.3 The steps involved in the formulation of outcome of failure scenarios and calculation of consequences are explained in the following diagram.
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FAILURE CASE DEFINITION TREE Nature of Hazard
Phase in the Process or Storage
Release Case
Event Tree Or Model (Ρ) Boiling Liquid Expanding Vapour Explosion 2.3.4 The Event Tree diagrams for gas and liquid release incidents are
presented in separate diagrams.
The flammable effects such as jet fire, flash fire, pool fire, fireball and vapour cloud explosion, are explained in the following section 2.4.0.
DEFINE INVENTORY & STORAGE CONDITIONS OF HAZARDOUS MATERIALS
FLAMMABLE
LIQUID OR TWO-PHASE LIQUID OR
TWO-PHASE GAS
TOXIC
GAS
BLEVE(Ρ)
OTHER CASES
BLEVE Model
Flammable Gas
Event Tree
Flammable Liquid
Event Tree
Toxic Gas
Event Tree
Toxic Liquid
Event Tree
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Is there Immediate Ignition?
FLAMMABLE LIQUID EVENT TREE
Is the Release Instantaneous?
Does a Pool Form?
Does the Pool Ignite?
Assess Fire Damage
Use Gas Event Tree to Model Gas Behaviour
Assess Pollution Use Gas Event Tree to Model Gas Behaviour
Assess Fire Damage
Assess Fire Damage
Use Gas Event Tree to Model Gas Behaviour
Assess Pollution Use Gas Event Tree to Model Gas Behaviour
Assess Fire Damage
No
Yes
Pool Fire
No
No
Yes
Yes
Estimate Duration Calculate Release Rate
Adiabatic Expansion
Yes
Release Case
Yes
No
No
Calculate Spread & Evaporation
Fire Ball
Pool Fire
No
Yes
Yes
No
Calculate Spread & Evaporation
Jet Flame
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2.2.5 Consequence analysis and calculations are effectively performed by computer
software using models validated over a number of applications. This report is based on PHAST software of DNV Technica, UK. PHAST is a major component of the risk analysis software PHAST RISK (previously known as SAFETI) used for consequence modeling. The consequence calculations perform dispersion modeling and effect modeling for each weather condition specified.
The dispersion modeling calculates the distances to critical concentrations, i.e. flammability limits for flammable materials, and to minimum toxic limits for toxic materials. The effect modeling is performed for flammable materials only, and calculates the distances to critical radiation levels for jet fires, pool fires and BLEVEs, and the distances to critical over-pressures for explosions.
The PHAST software uses the Unified Dispersion Model (UDM) capable of describing a wide range of types of accidental releases. The Model uses a particularly flexible form, allowing for sharp-edged profiles, which become more diffuse downwind.
2.2.6 The calculations by PHAST software involve following steps for each modeled failure case:
- Run discharge calculations based on physical conditions and leak size.
- Model first stage of release (for each weather category).
- Determine vapour release rate and pool evaporation rate.
- Dispersion modeling.
- In case of flammable release, calculate size of effect zone for fire and explosion.
2.2.7 The PHAST programme contains data for a large number of chemicals and allows definition of mixtures of any of these chemicals in the required proportion. Appropriate inputs for material, parameters, scenario and system details (pressure, temperature, size of opening etc.) are used in calculations for each failure case.
2.2.8 The stages involved in the calculations by PHAST are as follows:
(1) Input background data.
(2) Input failure cases.
(3) Select failure cases.
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(4) Run consequence calculations for selected cases.
(5) View results as graphs and tables.
The background data include material data, parameter data and weather data.
2.2.8 Weather data
Weather conditions are listed, each weather condition being a combination of wind speed and atmospheric stability. The weather data form important input to the dispersion calculations, and results for a single set of conditions could give a misleading picture of the hazard potential. The PHAST programme allows definition of a list of weather conditions, and it performs dispersion modeling for each condition in the list.
Stability class is a measure of the atmospheric turbulence caused by thermal gradients and it controls the vertical mass transfer mechanisms in the air, close to the ground. Six main categories (known as Pasquill stability classes) denoted by letters A - F are considered.
Stability Pasquill Stability Class
Temperature Gradient (deg. C per 100 metres)
Very unstable A
< (-)1 Unstable B
Slightly unstable C
Neutral D (-)1 to 0
Stable E 0 to 1
Very stable F > 1
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The basis for defining the stability parameter is illustrated in the following diagram.
(a) Unstable Conditions dT/dz < (dT/dz) adiabatic
(b) Stable Conditions dT/dz > (dT/dz) adiabatic
Neutral Conditions (dashed line) dT/dz = (dT/dz) adiabatic
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Relationship between wind speed and stability is given in the following table:
Wind Speed
Day Time:
Solar Radiation
Night Time: Cloud Cover
(m/s)
Strong
Mediu
m
Slight
Thin < 3/8
Mediu
m > 3/8
Overcas
t > 4/5
< 2 A A – B B - - D
2 - 3 A - B B C E F D
3 - 5 B B – C C D E D
5 - 6 C C – D D D D D
> 6 C D D D D D
Category D (neutral) is the most probable in moderate climates, and may occur for up to 80% of the time at relevant sites. It will almost always occur if the sky is heavily overcast.
Category F (stable) is generally associated with nighttime in cold weather and medium cloud cover. These conditions are not conducive to atmospheric dispersion. Category F is not possible over sea. This stability category is normally selected for considering worst-case scenarios.
It is necessary to consider a range of typical weather conditions in the consequence modelling calculations. PHAST software allows definition of multiple combinations of weather parameters.
The weather parameters required for PHAST are the following:
• Wind velocity
• Atmospheric weather stability class
• Atmospheric temperature
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• Relative humidity
• Surface roughness parameters
Based on the meteorological and weather data for the plant site, the following parameters are taken for consequence calculations to cover the conditions prevailing at different periods and seasons.
Parameter Unit Weather Condition
# 1 # 2 # 3
Wind Velocity (m/s) 3 3 5
Weather Stability Class B D D
2.3.0 Flammable Effects
2.3.1 The release of flammable gas or liquid can lead to different types of fire or explosion scenarios. These depend on the material released, mechanism of release, temperature and pressure of the material and the point of ignition. Types of flammable effects are as follows.
2.3.2 Pool fire: The released flammable material which is a liquid stored below its normal boiling point, will collect in a pool. The geometry of the pool will be dictated by the surroundings. If the liquid is stored under pressure above its normal boiling point, then a fraction of the liquid will flash into vapour and the remaining portion will form a pool in the vicinity of the release point. Once sustained combustion is achieved, liquid fires quickly reach steady state burning. The heat release rate is a function of the liquid surface area exposed to air. An unconfined spill will tend to have thin fuel depth (typically less than 5 mm), which will result in slower burning rates. A confined spill is limited by the boundaries (e.g. a dyked area) and the depth of the resulting pool is greater than that for an unconfined spill.
2.3.3 Flash fire: A flash fire occurs when a vapour cloud of flammable material burns. The cloud is typically ignited on the edge and burns towards the release point. The duration of flash fire is very short (seconds), but it may continue as jet fire if the release continues. The overpressures generated by the combustion are not considered significant in terms of damage potential to persons, equipment or structures. The major hazard from flash fire is direct flame impingement. Typically, the burn zone is defined as the area the vapour cloud covers out to half of the LFL. This definition provides a conservative estimate, allowing for
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fluctuations in modelling. Even where the concentration may be above the UFL, turbulent induced combustion mixes the material with air and results in flash fire.
2.3.4 Jet fire: Jet flames are characterized as high-pressure release of gas from limited openings (e.g. due to small leak in a vessel or broken drain valve). Jet fires can cause serious damage to equipment and people.
2.3.5 Boiling liquid expanding vapour explosion (BLEVE) or fireball: A fireball is an intense spherical fire resulting from a sudden release of pressurized liquid or gas that is immediately ignited. The best known cause of a fireball is a boiling liquid expanding vapour explosion (BLEVE). Fireball duration is typically 5 – 20 seconds.
2.3.6 Vapour cloud explosion: When a large quantity of flammable vapour or gas is released, mixes with air to produce sufficient mass in the flammable range and is ignited, the result is a vapour cloud explosion (VCE). Without sufficient air mixing, a diffusion-controlled fireball may result without significant overpressures developing. The speed of flame propagation must accelerate as the vapour cloud burns. Without this acceleration, only a flash fire will result.
2.3.7 The levels of heat radiation and explosion over-pressure considered for the analysis are based on the following reference publications:
• Loss prevention in the Process Industries by F. P. Lees
• Guidelines for Chemical Process Quantitative Risk Analysis published by AIChE / Center for Chemical Process Safety (CCPS)
• PHAST & SAFETI User Manuals of DNV Technica
• Gas Explosion Handbook published by GexCon
2.3.8 Flammable Models and End-points
Pool fire, Jet flame and BLEVE
Radiation Level (kW/m2)
Observed Effect
4 Sufficient to cause pain to personnel if unable to reach cover within 20 seconds; however blistering of the skin (second-degree burn) is likely; 0% lethality.
12.5 Minimum energy required for piloted ignition of wood, melting of plastic tubing.
37.5 Sufficient to cause damage to process equipment.
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2.3.9 The effect of thermal dose can be understood from the following correlation.
Thermal Dose (kJ/m2)
Burn Effect
65 Threshold of pain, no reddening or blistering of skin. 125 First degree burns (Persistent redness). 200 Onset of serious injury. 250 Second degree burns (Blistering). 375 Third degree burns (Charring).
Note: Thermal Dose = (Heat radiation intensity)4/3 x (Time) Units: Thermal dose – kJ/m2 Heat radiation intensity – kW/m2 Time - seconds
2.3.10 Explosion Parameters
An explosion results from a very rapid release of energy. The energy release must be sudden enough to cause local accumulation of energy at the site of explosion. The damage from an explosion is caused by the dissipating energy. The explosion energy causes the air to expand rapidly, forcing back the surrounding air and initiating a pressure wave (also called blast wave), which moves rapidly outward from the blast source. The pressure wave contains energy, which results in damage to the surroundings. For chemical plants, much of the damage from explosions is done by the pressure wave. The maximum pressure over ambient caused by the pressure wave is called the peak over-pressure.
The general correlation between explosion over-pressure level and the damage caused is given in the following table.
Over-pressure Observed Effect bar(g) psig
0.021 0.3
“Safe distance” (probability 0.95 of no serious damage below this value); projectile limit; some damage to house ceilings; 10% of window glass broken.
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0.069 1 Repairable damage; partial demolition of houses, made uninhabitable; steel frame of clad building slightly distorted.
0.138 2 Partial collapse of walls of houses.
0.207 3
Heavy machines (3000 lb) in industrial buildings suffered little damage; steel frame building distorted and pulled away from foundations.
2.3.11 Effect of explosion overpressure on humans can be seen from the following data:
Effect Explosion overpressure (psi)
Eardrum rupture - 1 % probability (threshold) 2.4 - 10 % probability 2.8 - 50 % probability 6.3
Skin laceration threshold 1 – 2
Serious wound threshold 2 – 3
Serious wound near 50 % probability 4 – 5
2.4.0 Toxic Effects
2.4.1 It is necessary to specify suitable concentration of the toxic substance under study to form the end-point for consequence calculations. The considerations for specifying the end-points for the hazardous material involved in the failure scenario are described in the following paragraphs.
2.4.2 American Industrial Hygiene Association (AIHA) has issued Emergency Response Planning Guidelines (ERPG) for many chemicals.
• ERPG-1 is the maximum airborne concentration below which it is believed that nearly all individuals could be exposed for up to 1 hour without experiencing other than mild transient adverse health effects or perceiving a clearly defined, objectionable odour.
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• ERPG-2 is the maximum airborne concentration below which it is believed that nearly all individuals could be exposed for up to 1 hour without experiencing or developing irreversible or other serious health effects or symptoms, which could impair an individual's ability to take protective action.
• ERPG-3 is the maximum airborne concentration below which it is believed that nearly all individuals could be exposed for up to 1 hour without experiencing or developing life-threatening health effects.
Where available, the ERPG values are useful for consideration in the consequence calculations. Where the ERPG values are not available, temporary emergency exposure limit (TEEL) values published are used. The definitions for the TEEL values are similar to ERPG.
2.4.3 Toxic limit values as Immediately Dangerous to Life or Health (IDLH) concentrations are issued by US National Institute for Occupational Safety and Health (NIOSH). An IDLH level represents the maximum airborne concentration of a substance to which a healthy male worker can be exposed as long as 30 minutes and still be able to escape without loss of life or irreversible organ system damage. IDLH values also take into consideration acute toxic reactions such as severe eye irritation, which could prevent escape. IDLH values are used in selection of breathing apparatus.
2.4.4 Significant flammable properties of NG used in the plant and considered in this study is summarized in the table below:
Chemical
Normal Boiling Point
Flammable Properties Toxic properties
Flash Pt.
LEL UEL Auto Ign. Temp.
ERPG-1 ERPG-2 ERPG-3 IDLH
(Units) (°C) (°C) (%) (%) (°C) (ppm) (ppm) (ppm) (ppm)
Methane (-) 161.5 NA 5 15 537.7 15000 25000 50000
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3.0 DATA FOR RISK ASSESSMENT
3.1 Site Location
Nagarjuna Fertilizers & Chemicals Limited (NFCL) is located at Kakinada,
East Godavari District of Andhra Pradesh. The total area covered by the
NFCL plant is about 380 acres is situated about 500 meters from the coast
just next to Kakinada bay. The site is about 2.5 meters above mean sea level.
It is surrounded on the north by Godavari Fertilizers and Chemicals Limited,
Bay of Bengal on the East, Kakinada town on the west and green belt on the
south. The width of the green belt is 1 km wide and it also extends on the
west. Incidentally the green belt is between the plant and the town. The site
plan is enclosed as Figure 2.1
3.2 Fertilizer Complex
The NFCL complex consists of two ammonia and two urea plants. The
ammonia plants are based on Haldor Topsoe Technology and urea plants on
Snamprogetti, total recycle with ammonia stripping. Ammonia Plant II was
switched over to natural gas from Naptha during the min-revamp . The
shortage of CO2, would be made by a 450 MTPD Carbon Di Oxide Recovery
Plant from the flue gases of Ammonia Plant I Primary Reformer stack. The
production capacity of ammonia plant-1 is 1325 MTPD and ammonia plant -2
1300 MTPD. Similarly, Urea-1 is 2325 MTPD and Urea-2 2281 MTPD.
NFCL is going in for a 400 MTPD Customised Fertilizer Granulation (CFG) Plant. This plant would be put up inside the existing complex.
3.3 The Data Requirements:
a. Chemical inventories in various process and storage units (vessels, tanks)
b. Properties of the chemicals c. Meteorological Data
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d. Demographic Data
NG line to HAG
Line Dia inch Line Length m
(from main header to HAG burner)
Pressure Kg/cm2
Temp °C Flow Nm3/hr
2 650 6.3 – 8.5 40 / 55 161.1 – 426.5
Materials The MSDS of the chemicals are enclosed as Annexure 1.
3.5 Site and Equipment Layout
Site Plan and Layout Plan for the plant are given in Figures 2.1 and 3.1
respectively.
3.6 Meteorological Data
The role of the atmosphere in dilution and dispersion of the accidentally
released hazardous chemicals is not very well understood in view of the
hydrodynamic complexities. The atmosphere acts like a large non-
Sl. No. Raw Material Approximate inventory Maintained
(MT)
Storage Mode
1 Di Ammonium Phosphate (DAP)
1800 Filled Bags
2 Urea 200 “ 3 Murate of Potash (MOP) 500 “ 4 Ammonium Sulphate 50 “ 5 Dolomite (Filler) 500 “ 6 Sulphur 10 Bulk / Filled
Bags 7 Zinc Sulphate 50 Filled Bags 8 Micro Nutrients 10 “
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homogeneous reactor with several simultaneous and often complementary
phenomena occurring. The notable parameters for assessing the atmosphere
are wind speed its direction and profile, micrometeorology and atmospheric
stability and topographic parameters.
The meteorological data compiled by India Meteorological Department (IMD)
for Kakinada has been used for the risk assessment computations. The
annual mean air temperature is taken as 28 Degrees C and mean % humidity
as 72%. The average velocity is taken as 3.2 m/s.
Atmospheric stability is a very important factor for predicting the dispersion
characteristics of gases/vapours of the surrounding environment. Change in
atmospheric stability is due to the direct consequence of its vertical
temperature structure. For a given location, this tends to vary from season to
season. The stability effects are mathematically represented through Pasquill
parameters. The following stability classification is employed.
Stability Class Atmospheric Condition A Very Unstable B Unstable C Slightly Unstable D Neutral E Stable F Very Stable
Six stability classes from A to F are defined while wind speed can take any one of the innumerable values. It may thus appear that a large number of outcome cases can be formulated by considering each one of very many resulting stability class-wind speed combinations. In fact the number of outcome cases that needs to be considered for formulating outcome cases in any analysis is very limited. In nature only certain stability class and wind speed occur. For instance A-3 m/s or B-5 m/s or F-4 m/s do not occur in nature. As a result only one or two or three stability class-wind speed combinations need to be considered to ensure reasonable completeness of the Risk Assessment.
The stability class distribution over the years works out as below:
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Month Wind Speed Cloud cover
(oktas) Stability Class
Km/hr m/s Day Night Day Night Jan 10.3 2.9 2.0 1.5 B E Feb 8.8 2.4 2.2 1.5 B E
March 8.3 2.3 2.3 1.3 B E April 9.1 2.5 3.7 2.3 B E May 11.1 3.1 4.3 3.0 B E June 12.1 3.4 5.1 5.1 D D July 12.3 3.4 6.1 6.0 D D Aug 11.0 3.1 5.6 5.7 D D Sep 8.6 2.4 5.4 5.5 D D Oct 9.5 2.6 4.5 4.8 B E Nov 12.0 3.3 3.4 3.6 B E Dec 11.3 3.1 2.2 2.2 B E
The cloud cover data: January – May 1.3 – 4.3 oktas June – October 4 – 6.1 oktas November – December 2.2 – 3.6 oktas
B 33% (day other than monsoon) D 17% (day –monsoon) & !7% (night- monsoon) E 33% (night other than monsoon)
For our study D-3m/s, D-5.0 m/s and B-3m/s stability class-wind speed combinations are considered. A most advanced method of estimating the dispersion parameters has been employed in which the input data requires the vertical temperature, wind profile and roughness factors.
3.7 Demographic Data: The following population has been considered: 0.5 km radius : 650 1.0 km radius : 6641
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2.0 km radius : 12660 3.0 km radius : 37129 5.0 km radius : 73236
The day and night population has been assumed to be the same. The consequences for various outcome cases – mainly toxic exposure – depend on whether people stay indoor or outdoor. The assumptions made Is as under: Day time 30% indoor, 70% outdoors Night time 70% indoor, 30% outdoors
3.8 Wind Direction
The annual frequency distribution of wind directions between 0830 hrs and 1730 hrs is tabulated below:
N NE E SE S SW W NW Calm 0830 hrs 4 24 1 5 1 37 7 9 12 1730 hrs 0 11 7 36 8 28 5 3 2
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4.0 VISUALISATION OF MAXIMUM CREDIBLE ACCIDENT
SCENARIOS
4.1 The starting point of Risk Assessment Study is the identification of hazards
and selection of scenarios that are then addressed for further analysis.
Hazard is defined as a chemical or physical condition that has the potential
for causing damage to people, property or environment. A number of
techniques are available for hazard identification depending upon the depth
and objective of the study.
Accidental release of toxic vapours or flammable vapour cloud can result in
severe consequences like toxic vapour cloud or vapour cloud explosion.
Delayed ignition of flammable vapours can result in blast over pressures.
Toxic clouds cover large distances due to lower concentration threshold
value.
In contrast, fires have localized consequences. The extent of damage to
people depends on the heat flux and duration of exposure. Fires can be put
out or contained in most cases.
Hazards, in process plant, are primarily identified on the following information:
Hazardous properties of materials handled during the process
Types of unit process / unit operation
Operating pressure / vacuum / temperature
4.2 Maximum Credible Accidents and Consequence Analysis (MCACA)
MCACA is a scientific technique to identify the vulnerable areas in a plant
where sudden heavy release of toxic vapours or flammable vapour is a
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probability. Such releases can create unsafe situations to the personnel
inside the plant, people in the surrounding area and to the environment.
MCACA aims at identifying the most credible unwanted accidents, which can
cause maximum damage. For this purpose, a number of probable or potential
accident scenarios have been visualised, examined, screened to select only
the most probable events and their credibility established. These incidents are
called Representative incidents.
4.3 Methodology Followed for Selection of Release Scenarios
In the European countries and USA there are statutory guidelines for the
selection of release sources for performing Risk Analysis of Industrial
installations. In this study the release of natural gas from the 2” header
supplying fuel to the HAG due to line rupture has been considered since all
other materials handled are solid and non-hazardous.
This consequence analysis gives:
a. Description of the potential accident (rupture of pipeline)
b. Estimation of the quantity of material released (flammable, explosive)
c. Where appropriate, a calculation of dispersion of material released
(gas)
d. Assessment of harmful effects (heat radiation, blast wave)
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4.4 Maximum Credible Accident Scenarios
As mentioned else where, in this study the release of natural gas from the 2”
header supplying fuel to the HAG due to line rupture has been considered
since all other materials handled are solid and non-hazardous
Sl. No
Release Source Failure Mode Outcome Modeled
1
2” Natural Gas Line
Guillotine failure Jet Fire, and Flash Fire.
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5.0 CONSEQUENCE ANALYSIS
5.1.0 Introduction
5.1.1 The major criterion for selection of scenarios is the potential for high hazard considering the amount of hazardous substance involved, operating conditions, and possibility of release and extent of consequence.
5.1.2 The details regarding the natural gas have been furnished in an earlier section of this report. The consequence calculations are based on that data.
5.1.3 The analysis of the scenario selected for study of the CFG plant is presented in the following paragraphs.
Tabular reports and graphic plots are presented wherever appropriate.
5.2.0 Failure scenario
The following scenarios have been considered for consequence calculations.
Sl. No
Release Source Failure Mode Outcome Modeled
1
2” Natural Gas Line
Guillotine failure
Jet Fire, and Flash Fire.
The main hazards are due to handling of flammable natural gas.
The levels of heat radiation for the analysis are based on the following reference
publications:
• Loss prevention in the Process Industries (2nd Edition) by F. P. Lees
• Guidelines for Chemical Process Quantitative Risk Analysis by American Institute of Chemical Engineers (AIChE) / Center for Chemical Process Safety (CCPS)
• PHAST & SAFETI User Manuals of DNV Technica
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Flammable Models and End-points
Pool fire, Jet flame and BLEVE
Radiation Level
(kW/m2)
Observed Effect
4 Sufficient to cause pain to personnel if unable to reach cover within 20 seconds; however blistering of the skin (second-degree burn) is likely; 0% lethality.
12.5 Minimum energy required for piloted ignition of wood, melting of plastic tubing.
37.5 Sufficient to cause damage to process equipment.
The general correlation between explosion over-pressure level and the damage caused is given in the following table.
Over-pressure
Observed Effect Bar(g) Psig
0.021 0.3 “Safe distance” (probability 0.95 of no serious damage below this value); projectile limit; some damage to house ceilings; 10% of window glass broken.
0.069 1 Repairable damage; partial demolition of houses, made uninhabitable; steel frame of clad building slightly distorted.
0.138 2 Partial collapse of walls of houses.
0.207 3 Heavy machines (3000 lb) in industrial buildings suffered little damage; steel frame building distorted and pulled away from foundations.
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Consequence modeling calculations were carried out using the software PHAST Micro 6.1 of DNV TECHNICA. Graphs obtained as output of the software are presented and summary of the results are tabulated in the following pages.
Summary of Result: For the scenario selected, the outcome cases are considered for the atmospheric conditions 3B, 3D and 5D. The first numeral represents the wind speed in meters per second and the subsequent alphabet represents the stability class. Sl. No Scenario Wind
Velocity / Stability
Damage Distance (m) Radiation Level Jet Fire Ellipse
Flash Fire Envelope
37.5 kW / m2
12.5 kW / m2
4 kW / m2
Furthest Extent 21716.9 ppm
Furthest Extent 43433.9 ppm
1
2” NG line to HAG rupture
3 B 9.94 10.50 11.85 7.81 5.17
3 D 10.26 10.68 12.0 7.84 5.15
5D Not Reached
10.78 12.26 6.56 4.70
The graphs for flash fire envelope, intensity radii for jet fire and Radiation vs Distance for Jet fire are shown in the following pages.
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6.0 PROBABILITY OF OCCURRENCE FOR SELECTED
SCENARIOS
6.1 Risk Factor Risk is defined as, “a combination of uncertainty and damage” and “a triple
combination of event, probability and consequence”. Risk estimation
combines the consequences and likelihood of all incident outcomes from
related incidents to provide a measure of risk, but these estimates based
on mathematical models have the limitation of not covering all factors
existing in the real scenario. This limitation must be appreciated by
management to set reasonable goals.
6.2 Probability estimation
The probability estimation is done by different theoretical methods such as
fault tree analysis, event tree analysis etc. The likelihood can be estimated
theoretically. But where the design involved is sufficiently similar to existing
designs represented in the historical records available in the literature, the
incident frequency can be derived from historical statistics. Only where the
design is substantially different and historical data do not exist the fault tree
method is adopted.
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The probability or frequency of occurrence for piping related to the scenario
identified in Chapter 4 is as under:
Description Type of Failure Failure Rate
Piping - Small
(≤ 50 mm Dia.)
Rupture 8.8 x 10 -7 (m.yr)-1
(m.yr)—1 means per metre per year
Ignition Probability
Historical data on ignition of flammable releases has been used as a basis for determining Ignition probabilities.
Type of ignition Probability Immediate 0.065 Delayed 0.065
No ignition 0.87 The conditional possibility of explosion is 0.67.
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7.0 RISK OF AUTO IGNITION, RISK OF CHEMICALS UNDER PRODUCTION, HANDLING, STORAGE AND
TRANSPORTATION, RISK DUE TO ELECTRICAL SHORT CIRCUITING OR ANY OTHER SOURCE, THREATS FROM THE EXISTING PLANTS
7.01 Materials Handled in CFG Plant
The details of raw materials and micro nutrients which are used in the
production of CFG are given in Table 7.1.
These materials are fed to the paddle mixtures from the storage bins in pre-
determined quantities. There is no chemical reaction but only physical mixing.
The premixed mixture is granulated, dried, screened and bagged after
precoat. Sl. No
Name of Chemical
Decomposition Temperature
Deg. C
Products of Decomposition
Approximate Quantity Stored
(MT)
Mode of Storage
1 DAP
155
Release of ammonia and oxides of phosphorus
1800
Filled Bags
2
MOP
Sublimes at 1500 deg C
When subjected to extremely high temperatures small quantities of chlorine is liberated.
500
Filled Bags
3
Urea
122.7
Ammonia, oxides of nitrogen, cyan uric acid, cyanic acid, biuret and CO2
200
Filled Bags
4 FeSO4 > 300 Sulphur Oxides
10 Filled Bags
5 Zn SO4
600
Fumes of SOx
50
Filled Bags
6 Ammonium
Sulphate
280
Ammonia, Sulphur trioxide and Sulphur di-oxide
50
Filled Bags
7 Dolomite 870 Ca and Mg oxides and CO2
500 Filled Bags
8 Borax
None 10 Filled Bags
9 Sulphur Boiling Point 444.6 Sulphur di-oxide and H2S under certain conditions
10 Bulk / Filled Bags
Table 7.1
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7.02 Risk of Chemicals under Production, Handling, Storage and
Transportation
When the materials are subjected to extreme high temperatures during an
external fire, there is a possibility of the chemicals decomposing to release
limited quantity of toxic by-products of decomposition (e.g., Ammonia,
Chlorine sulphur dioxide etc.,).
The materials stored, handled and mixed is thermally stable at normal working
conditions during storage and transport. The materials do not have the
tendency for auto ignition based on their chemical characteristics. They will
not get ignited due to normal ignition sources and heated metals. So there is
no possibility of fire taking place in the storage area due to auto ignition, hot
work etc., and leading to emission of toxic gases from the stored materials.
The available literature does not mention about any evolution of toxic gases to
that extent that it needs dispersion/consequence modeling.
Precautions to be taken during Storage & Handling to minimize/mitigate the risk
The quantity of the raw materials being limited and also since they are stored
in bags (which means that they can be segregated and stacked as per good
practices to provide separation distance as well as access), the possibility of
an external fire leading to a major emergency scenario (release of toxic by
products of materials) is very remote. The following are the precautions
suggested to prevent and or mitigate the risk due to decomposition of
materials due to external fires:
1. Special care should be taken to avoid the storage of raw materials in
close proximity to combustible materials such as wooden pallets,
packaging materials etc.,
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2. It is to be ensured that free access is made available to the storage
area for emergency and fire-fighting equipment to be used in the event
of a fire/decomposition.
3. The storage area should have provision for ventilation to dilute the
concentration of toxic by-products/fumes as a result of any external
fire.
4. Self contained breathing apparatus (SCBA) and suitable protective
clothing should be made available in the vicinity of the storage and
these should be worn while attending to any fires in the storage area.
7.03 Risk Due To Electrical Short Circuiting A short circuit in an electrical circuit is one that allows a current to travel along
a path where essentially no (or a very low) electrical impedance is
encountered. Short circuits occur mainly due to overloading as it leads to
heating effect and may result in fire breakout and fatal accidents, if proper
instructions are not followed. Electrical fires spread rapidly and cause loss of
lives and property.
Such incidents can be minimized to a great extent if the under noted
precautions are observed.
1. Always use good quality cables.
2. Make sure that electrical outlets are designed to handle
appliance loads.
3. If an electric appliance smokes or gives away an
unusual smell, unplug it immediately, then do the
proper servicing before using it again.
4. Avoid joints in wiring (taping of wires). Instead, use
extension box with fuse or else go for soldering and
proper mechanical joints.
5. Always renew the wiring after ageing. Replace
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electrical cords that are cracked or frayed.
6. Use adequate capacity fuses for protection. Do not
increase the ratings without ascertaining reason of fuse
blowing. Do not tamper with fuse box. Install the Fuse
board away from combustible materials like paper, oil,
curtains etc.
7. Keep flammable material (oil etc.) safely in special
containers.
8. Disconnect electrical tools and appliances when not in
use.
9. Use correct rating Earth Leakage Circuit Breaker
(ELCB). A leakage current even of 1 ampere can cause
electrical fire. A correctly chosen ELCB can detect the
leakage current and can cut-off circuit thus reducing
the fire-risk.
10 The lighting fixtures should be suitable service in a
particular area.
7.04 Threats from the existing plants
The CFG Plant is to the west of existing cooling tower of Ammonia Plant-II
and north west of Urea Plant-II cooling towers. Any release of chlorine from
the cooling towers might affect the personnel in this plant subject to the
direction of the wind.
Similarly any major ammonia release from ammonia and / or urea plants
would have an effect on the personnel working in CFG Plant, again, subject to
wind direction.
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8.0 CONCLUSIONS AND RECOMMENDATIONS
8.1 Conclusions
Ever since the commissioning of the NFCL plants (Ammonia & Urea) there
has been no major release of Natural Gas leading to a fire situation. The
CFG plant appears to be well designed and adequately instrumented for
its safe operation.
With the extension of current predictive and preventive maintenance
practices and testing and calibrating procedures to the NG line and CFG
plant, there appears to be no major risk of a major natural gas release and
subsequent fire hazard.
8.2 Review of Risk Analysis Study The major risk is due to accidental NG release resulting in fire and
explosion. The scenario of NG gas line rupture to HAG resulting in Jet and
Flash fires would not result in Off-Site emergency since the damage
distances would be confined to the factory premises. The quantity of gas
released, assuming effective action is taken to cut off the gas with in 5
minutes, may not result in explosion and consequent damage due to over
pressure.
General Recommendations The two steps generally considered in Risk reduction in the CFG plant are
(a) Reduction of consequences and (b) Reduction of likelihood of an
accident release of NG.
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Some of the measures to reduce consequence are:
a) Automatic Shut Down
b) Effective maintenance System & safety devices
c) Safety Management System (SMS)
Automatic Shut Down
The quantity of material escaping from containment or from the NG line, in
case of line rupture, would get completely cut off if automatic shut down is
available and a release takes place.
Maintenance System and Safety Devices
A number of instruments are provided for the safe operation of the NG line
to HAG burner and CFG plant. Scheduled and effective maintenance of
instruments and safety devices may prevent, to a very large extent, failure
resulting in release of flammable gas
Safety Management System (SMS)
The Unit has a well documented Safety Management System (SMS)
covering a number of elements. By effective Safety Management System,
to a very large extent, failures may be prevented.
8.3 Specific Recommendations Special attention in terms of inspection and safety management systems
for NG line is suggested.
A portable explosimeter will be utilized to identify the leaks from time to
time.
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Production, Handling, Storage and Transportation
Electrical fittings should conform to the service. All sources of heat must be kept away from fertilizers. Potential heat sources include light bulbs,
heating systems, steam pipes, electric motors, live electrical cabling and
naked flames.
Electrical Short Circuiting
The recommendations made below, if followed might obliterate fires and
consequent damages due to electrical short circuit
The lighting fixtures in the NG routing and HAG area should conform to
the standards suitable for service in that area and once installed must be
maintained.
Use only ISI certified appliances.
Use good quality fuses of correct rating, miniature circuit breakers
and earth leakage circuit breakers.
Use one socket for one appliance.
Switch off the electric supply of the fire affected areas.
Fuses and switches should be mounted on metallic cubicles for
greater safety against fire.
Replace broken plugs and switches.
Keep the electrical wires away from hot and wet surface.
Don’t use substandard fixtures, appliances.
Never have temporary or naked joints on wiring.
Don’t lay wires under carpets, mats or doorways. They get
crushed, resulting in short circuiting.
Don’t lay wires under carpets, mats or doorways. They get
crushed, resulting in short circuiting.
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Don’t allow appliances cords to dangle.
Don’t place bare wire ends in a socket.
No combustible material should be permitted to be stored in the
plant
Threats from the Existing Plants With the current predictive and preventive maintenance practices and
testing and calibrating procedures, the probability of a major gas release
from the existing units appears to be very remote.
Mock drills should be conducted posting necessary observers.
Information pamphlets may be issued which would serve as a refresher
briefing to all the employees detailing how to respond in case of an
emergency.