Process Safety Engineering.pptx

PROCESS SAFETY ENGINEERING MODULE-1

Process Safety • Process safety is a blend of engineering and management skill focused on preventing catastrophic accidents, particularly fire, explosion, toxic gas release associated with use of chemical and petroleum products.

• Process safety is the proactive identification, evaluation and mitigation of chemical releases that could occur as a result of failure in process, procedure or equipment.

Objective of Process Safety • Prevention or minimize the consequence of catastrophic release. • Minimize the consequence to employees and community.

• • • •

1. Process safety engineering 2. Process safety management. PSM is a performance based safety. It is a people based and performance based safety not paper based safety (ISO).

Process safety strategies – In order to improve the process safety in , we have four methods 1.Inherent 2. Passive 3. Active 4. Procedural

Process Safety Management • PSM by OSHA • RBPSM by CCPS • The Occupational Safety and Health Administration (OSHA) created the first PSM requirements in 1992 in response to a series of catastrophic incidents related to highly hazardous chemicals (HHC).

What is Process Safety Management? • PSM: – Addresses the management of Highly Hazardous Chemicals (HHC) – Integrates • Technology • Operating Procedures • Standard management protocols

PHSER in Process safety • • • • • • •

PHSER in conceptual design PHSER in FEED PHSER in detailed engineering PHSER in construction PHSER in pre commissioning (PSSR) PHSER in normal operation PHSER in expansion/modification/ debottlenecking. • PHSER in decommissioning.

14 elements of PSM • • • • • • • •

Employee participation Process safety information Process Hazard analysis Operating procedure Training Contractors Prestart up safety review Mechanical integrity

• • • • • •

Hot work permit Management of change Incident investigation Emergency planning Compliance audit Trade secret

Safety • Safety is the prevention of accident and the mitigation of personal injury or property damage which may result from accident. • Safety is a condition resulting from the modification of human behaviour and or designing the physical environment to reduce the possibility of hazards, there by reducing accidents.

• A successful safety program require several ingredients. • System – outstanding safety programme • Attitude • Fundamentals – of CPS in the design, construction and operation of the plant • Experience • Training • You

Accident • Accident may be defined as an unplanned, non controlled and undesirable event or sudden mishap which interrupts an activity or a function which has the potential to cause injury or property damage. • Injury- may be defined as the bodily hurt sustained as the result of the accident such as laceration , abrassion, wound, fracture etc.

Sequence of Injury • • • • • •

Social environment Fault of a person Unsafe act or condition Accident Injury This is called Domino theory by Heinrich.

Reportable accident • Any accident in a factory which causes any bodily injury by reasons of which the concerned worker is prevented from working for a period of 48 hrs or more it become reportable accident. • Hazard-hazard is a condition or set of condition that have the potential to produce injury or property damage. • Risk- risk refers to probability that a hazard will be activated and produce injury or property damage.

• Event sequence – a specific unplanned sequence of events composed of initiating events and intermediate events that may leads to an incident. • Eg: rupture of pipe line, corrosion resulting in leak. • Incident – the loss of containment of material or energy. Leak of ammonia from a connecting pipe line to the ammonia tank, producing a vapour cloud. Not all events propagate into incidents.

• Incident outcome/ Accident – physical manifestation of the incident. • For toxic material – toxic release • Flammable material – BLEVE, Flash fire, UVCE. • Classes of Incident• 1. Localized incident – local effect zone (pump fire) • 2. Major incident – medium effect zone (with in the plant) • 3. Catastrophic incident – large effect zone ( surrounding community)

Unsafe act • Unsafe act may be defined as a departure from an accepted, normal or correct procedure or practice that leads to an unnecessary exposure to a hazard. • Unsafe condition – may be defined as any physical condition that if left uncorrected leads to an accident.

Accident and loss statistics • Many statistical methods are available to characterize accident and loss performance. • 1. OSHA incident rate • (Number of injuries and illness/Total hours worked by all employees during period covered) X 200000 • A worker assumed to spend 2000 hours (50 weeks x 40 hours). 100 workers.

• 2. Fatal accident rate- British chemical industry • (Number fatalities/ Total hours worked by all employees during period covered) x 100000000 • 1000 employees working their entire life time. The employees are assumed to work a total of 50 years.

• 3. Fatal rate or death per person per year. • (Number of fatalities per year/ total number of people in applicable population) • 4. Frequency rate (ILO) • (Number of lost time accident/ Total number of man hours worked) x1000000 • 5.Severity rate (ILO) • (Number of man days lost/ Total number of man hours worked)x1000000.

• An undertaking with 500 workers, working 50 weeks of 48 hours each, had 60 accidents during one year. Owing to illness, accidents and other reason the workers were absent during 5% of the aggregate working time. The number of days lost due to the 60 accidents alone was 1200. calculate the frequency and severity rates.

• Total man hours worked = 500x50x48 = 1200000 • Absence man hours = 1200000 x 5% = 60000 • Man hours of exposure = 1140000 • Frequency rate =( 60/1140000) 1000000 = 52.63 • This indicate that in a year about 53 accident occurred per million man hours worked.

• Severity rate = (1200/1140000)x1000000 = 1053.

Safety in Chemical Industry Chemical industries are complex systems with innumerable chemicals being used at various phases of operations.

The safety requirements of each industry are unique and tailor made for the particular entity. Safe operating practices and procedures are important in the Process Industry because the work is hazardous, involving massive machinery, extreme process conditions... The raw materials, process, intermediate products, final products and waste products in the operations have a number of associated hazards.

Oil Tanker at Karunagappalli

Fire at IOC Jaipur depot

Bhopal Gas Tragedy • 41 T of MIC and its reaction products released • Cold winter midnight of 2nd – 3rd December 1984 • Between 00:40 and 02:30 AM approx.

• At 30m (100ft) height • Moved as a 10m (30ft) high wall • Covered residential areas, 65 sq. km. Area Approx. 8000 immediate deaths, • Over 12000 more died since, over 120,000 still suffering

The design did not provide a backup system to divert escaping MIC to an effluent area for quick neutralization

The Safety Hierarchy…

• • • • • • •

The preferred approach in addressing hazards is: 1. 2. 3. 4. 5. 6.

Eliminate the hazard by design Substitute less hazardous work methods or materials Incorporate safety devices (guarding systems) Provide warning systems Apply administrative controls (work methods, training) Provide personal protective equipment (PPE)

Chemical Industry • • • • •

Chemical Industries Handle Store & Process Large quantities of hazardous chemicals and intermediates with high damage potential.

Chemical Industry • Substances in storage & • Stressful operating conditions such as high pressure, high temperature, or controlled exothermic reactions • Pose considerable risk to those working in industry and the neighbouring areas.

Main hazards • • • • • •

Any major source of harm is known as hazard Major hazards in chemical industry : Fire Explosion Release of toxic chemicals The hazard along with its probability of occurrence is called Risk.

Hazardous Chemicals • • • • • • •

Characteristics which make a substance hazardous : Flammability Explosivity Toxicity Reactivity Corrosivity Radio activity

Industrial disasters • • • • •

Major disasters in chemical industry : Flixborough, Seveso, Mexico Bhopal etc.

Heinrich’s principle Based on analysis on over 550 thousand occupational accidents 1 for Serious Injury

H. W. Heinrich got the 1-29-300 principle from his analysis on over 550 thousand occupational accidents. The accidents were classified into 3 categories of serious injury (lost work-day: more than one day), slight injury (no lost work-day) and not injured.

29 for Slight Injury

300 without Injury

Accidents are a Part of the Iceberg

Hazard and Risk • Hazard- defined as condition or set of condition that have potential to produce injury or property damage. Hazard by itself will not produce injury it needs an outside stimulus. • Risk- risk refers to probability that a hazard will be activated and produce injury or property damage.

Risk analysis • The word Risk is meant as likelihood of occurrence of a hazard and quantification of degree of damage, fire, injury or loss, fatality- in that hazardous event. Alternative definitions of risk -Risk is a combination of uncertainty and damage • Risk is a ratio of hazards to safeguards • Risk is a triple combination of event, probability and consequence

• Risk analysis is a quantitative estimate of risk based on engineering evaluation and mathematical techniques for combining estimates of incident consequence and frequencies • • Risk assessment is the process by which the results of risk analysis are used to make decision, either through a relative ranking of risk reduction strategies or through comparison with risk target. Identify and prioritize potential reduction measure if the risk is considered to be excessive

SPECIAL HAZARDS OF CHEMICALS • TOXICITY- Substances are considered toxic if they have some adverse effect on the human body. • Units of toxicity- lethal dose for rats which is determined under standard laboratory condition. It is usually expressed as LD50, defined as that dose administered orally or by skin absorption which will cause the death of 50 percentage of the test group within a 14 day observation period.

• It is generally expressed as mg/Kg of body weight. Since LD50 is based on oral or dermal entry in to the body. Another unit is the lethal concentration LC50, is used for airborne material which are inhaled. This is defined as the concentration of airborne material, the four hour inhalation of which results in the death of 50 percentage of the test group within a 14 day observation period.

Toxicology • The way toxicants enter biological organisms – ingestion, inhalation, dermal absorption. • The way toxicants are eliminated from biological organism – excretion, detoxification, storage • The effects of toxicants on biological organismdose V/S response • Methods to prevent or reduce the entry of toxicants into biological organism – industrial hygiene.

Classes of toxicitySuper toxic

<5 mg/kg

Extremely toxic

5-50 mg/kg

Very toxic

50-500 mg/kg

Moderately toxic

500-5000 mg/kg

Slightly toxic

5-15 g/kg

Practically non toxic

>15 g/kg

• Toxic chemical- chemical having following values of acute toxicity • LD 50 (oral)- 5 to 200 mg/kg of body weight • LD 50(skin)- 10 to 400 mg/kg of body weight • LC 50 – 0.1 to 2 mg/ inhalation

Substance with extreme health hazards • Carcinogenic – a substance which may induce cancer in man or increase its incidence • Teratogenic- a substance may involve a risk of subsequent non hereditable birth defects in offspring • Mutagenic- a substance which may involve a risk of hereditable genetic defects.

Standards for Occupational exposure • • • • • • • • •

OEL is published by HSE ,UK TLV is published by ACGIH, USA IDLH(NIOSH) PEL(OSHA) Types of TLV1. TLV-TWA 2. STEL 3. TLV-C MAC(max allowable ceiling)

• TLV- is defined as the concentration of substance in air that can be breathed safely for eight hours a day for five consecutive days a week by most people with out any adverse effect. • STEL- it is the maximum concentration to which worker can be exposed for a period up to 15 min continuously, for not more than 4 times per day, with at least 60 minutes between the exposure period and provided that daily TLV/TWA is not exceeded. • TLV-C- is the concentration that should not be exceeded even instantaneously

• • • •

C ppm = (22.4/M)(T/273) (1/P) (mg/M3) T = temp in K P= absolute pressure in atm M = Molecular weight.

• Air contain 5ppm of diethylamine (TLV-TWA of 10 ppm), 20 ppm of cyclohexanol (TLV-TWA of 50ppm) and 10ppm of Propylene oxide (TLVTWA of 20ppm). What is the mixture TLV-TWA and has this level been exceeded.

• (TLV-TWA)mix = 5+20+10/(5/10)+(20/50)+(10/20) =25 ppm • The total mixture concentration is 20+10+5 = 35 ppm • The workers are over exposed under these circumstances.

• Determine 8hr TWA worker exposure if the worker is exposed to toluene vapours as follows. • Duration of exposure ppm • 2 110 • 2 330 • 4 90

• TWA = C1T1 +C2T2+C3T3/(T1+T2+T3) • = (110(2) +330(2) +90(4))/8 = 155ppm • TLV for toluene is 100 ppm, the worker is overexposed. Additional control measures need to be developed.

Substance

TLV(PPM)

PEL(PPM)

Ammonia

25

50

Aniline

2

5

Benzene

10

1

CO

25

50

Cl2

0.5

1

cyclohexane

300

300

Vinyl chloride

5

1

Flammability hazards • Flammability simply means the ease with which a material burns in air. • Fire triangle- heat,oxygen,fuel • NFPA(USA)-hazard rating system-4 degrees of flammability. • Degree4- materials which will rapidly or completely vaporize at atm pre and normal temp or which are readily dispersed in air, and which will burn readily. • Gaseous material, cryogenic material, Class IA

• Degree 3-liquids and solids that can be ignited under almost ambient temp condition. • Class IB and IC flammable liquids • Degree2-materials that must be moderately heated or exposed to relatively high temp before ignition can occur.(class 2 and class3A) • Degree1- materials in this degree require considerable preheating before ignition and combustion can occur.(class 3B ) • Degree 0 – material that will not burn.

Classification of combustible liquids as per NFPA • • • • • • • •

Flammable liquids Class I A - F.P <22.8C,B.P <37.8C Class IB - F.P < 22.8C, B.P> 37.8C Class IC -F.P 22.8 to 37.8C Combustible class II – 37.8 – 60C Combustible class III A – 60 – 93.4C Combustible class IIIB >93.4C Class IA and IB liquids rate as highly flammable.

Fire V/S Explosion • Major distinction between fire and explosion is the rate of energy release. • Fire release energy slowly, where as explosion release energy rapidly, typically on the order of microseconds. • Fires can also result from explosions and explosions can result from fires.

Parameters of flammability • • • • • • • • • • • •

Flammability limits(gases and vapour) Flash point(liquids and low melting solids) Auto ignition temp Ignition energy Burning velocity Heat of combustion Oxygen requirement Specific gravity Solubility in water Melting points Viscosity c/H2 ratio

• Flammable gases- substance which in the gaseous state at normal pre and mixed with air become flammable and the boiling point of which at normal pre is 20C or below • Highly flammable liquid • Flammable liquid • Combustible liquid • Combustible solid

Types of fire • • • •

Pool fire Flash fire Jet fire Fire ball

Pool fire • If a flammable liquid at a temperature above its flash point spills, a part of the liquid will vapourise. • The resulting vapour above the liquid pool may form a flammable mixture. • If the vapour ignites, the result will be a diffusion flame on the surface of the pool, which is known as a pool fire. • A pool fire can be confined or unconfined. • Burns and damage due to heat radiation or flame contact.

Jet fire • A jet fire will appear as a long narrow flame produced. • Eg. From an ignited gas pipe line leak. • Damages due to flame impingement and consequential domino effects

Flash fire • A flash fire could occur if an escape of gas reached a source of ignition and rapidly burnt back to the source of the release.

BLEVE / Fire Ball • BLEVE / Fire Ball occurs within a vessel or a tank in which a liquified gas is kept above its atmospheric boiling point. • The accident is caused if a jet flame impinges upon the tank or if the tank gets engulfed by any external fire

• The tank pressure rises and at the same time the wall of the tank above the liquid level loses strength due to high temperature. • This results in the failure of the tank causing instantaneous release of its contents as a turbulent mixture of liquid and gas, expanding rapidly and dispersing in air as a cloud. • When this cloud is ignited, a fire ball occurs, causing an enormous heat radiation intensity within a few seconds.

Formation of BLEVE

Mexico City Holocaust

CISRA

POOL FIRES

KEROSINE

LNG CISRA

DEVELOPMENT OF POOL FIRE Release from an atmospheric tank

DEVELOPMENT OF POOL FIRE Release from an atmospheric tank

DEVELOPMENT OF POOL FIRE Spreading of vapours

DEVELOPMENT OF POOL FIRE Contact with source of ignition

DEVELOPMENT OF POOL FIRE Flash fire

Pool Fire • Pool Fire: – A fire of an spilled pool of flammable or combustible substance with the risk of burns to persons or objects within or around the flames.

TYPES OF FIRES • Flash Fire: – Ignition of a flammable gas/vapour and air mixture on finding a source of ignition.

TYPES OF FIRES • Jet Fire: – Jet of flame formed due to instantaneously burning gas/ vapour.

JET FIRE

CISRA

TYPES OF FIRES • BLEVE: – Boiling Liquid Expanding Vapour Explosion

Flammability limits • Vapour air mixture will ignite and burn only over a well specified range of compositions. The mixture will not burn when the composition is lower than the LFL, the mixture is too lean for combustion. • the mixture is also not combustible when the composition is too rich, that is , when it is above the UFL. • A mixture is flammable only when the composition is between the LFL and the UFL.

Relationships between various flammability properties

• The exponential curve represents the saturation VP curve for the liquid material. • UFL increases and LFL decreases with temperature. • The LFL theoretically intersects the saturation VP curve at the FP. • The AIT is actually the lowest temp of an autoignition region.

• What are the LFL and UFL of a gas mixture composed of 0.8% hexane,2% methane and 0.5% ethylene by volume.

Volume%

Mole fraction LFL Vol% on combustible basis

UFL vol%

Hexane

0.8

0.24

1.2

7.5

Methane

2

0.61

5.3

15

Ethylene

0.5

0.15

3.1

32

Total combustibles

3.3

Air

96.7

• • • • • •

LFL mix = 1/Ʃ(Yi/LFLi) LFL mix = 1/(0.24/1.2)+(0.61/5.3)+(0.15/3.1) = 2.75% by volume UFL mix = 1/Ʃ(Yi/UFLi) = 1/(0.24/7.5) +(0.61/15)+(0.15/32) = 12.9% by volume.

Estimating flammability limits • • • • • • • • •

LFL = 0.55(100)/(4.76m+1.19x-2.38y+1) UFL = 3.5 (100)/(4.76m+1.19x-2.38y+1) m = carbon number X = hydrogen number Y = oxygen number Heat of combustion of fuel LFL=(-3.42/Hc )+0.569Hc+0.0538Hc^2+1.8 UFL= 6.3Hc+0.567Hc^2+23.5 Hc is heat of combustion in KJ/mol

• • • • • • •

Estimate the LFL and the UFL for hexane C6H14 M=6 X=14 Y=0 LFL= 1.2% UFL = 7.5%

• Estimate LFL and limiting oxygen concentration (LOC) of butane. • C4 H10 • M=4, x = 10, y=0 • LFL =1.7 • LOC= LFL (moles of O2/moles of fuel) • C4 H10 +6.5 O2 4 CO2 +5H2O • 1.7 (6.5/1) = 11 Vol% of O2. • The combustion of butane is prevented by adding N2, Co2, or even water vapour until the O2 concentration is below 11 %.

Adiabatic Compression • Several large accidents have been caused by flammable vapours being sucked into the intake air compressors, susequent compression resulted in autoignition. • Adiabatic temp increase for an ideal gas is computed from the TD adiabatic compression equation • T2 = T1 (P2/P1)^ (gamma-1/gamma)

• What is the temp after compressing air over liquid hexane from 14.7psia to 500 psia if the initial temp is 100F. The AIT of hexane is 487C and gamma for air is 1.4.

• T2 = 373 (500/14.7)^ 0.4/1.4

• A particular lubricating oil has an AIT of 400C. Compute the compression ratio required to raise the temp of air to the AIT of this oil. Assume an initial air compressor of 25C and 1atm.

• P2/P1 = (T2/T1) ^gamma/(gamma-1) • (400+273/25+273)^1.4/0.4 • =17.3

Explosion • Explosion results from the rapid release of energy. The energy release must be sudden enough to cause a local accumulation of energy at the site of explosion. This energy must be dissipated by variety of mechanism, including formation of pressure wave , projectiles, thermal radiation and acoustic energy.

Parameters significantly affecting explosion • • • • • • • • • •

Ambient temp Ambient pressure Composition of explosive material Physical properties of explosive materials Nature of ignition source Geometry of surrounding Amount of combustible material Turbulence of combustible material Time before ignition Rate at which combustible material released.

Explosions • Explosion is a sudden release of energy that causes damaging pre waves in the atmosphere. In a chemical plant explosion can occur in several forms • Forms of explosions :• 1. deflagration • 2. detonation • 3. confined explosion • 4. unconfined explosion • 5. physical exploion

• Chemical explosion fall into two classes, explosive deflagration and detonation. • A deflagration is caused by a chemical reaction which passed through the deflagrating material at well below sonic velocity. It normally only develop an appreciable pre if it is confined. Most deflagrations are thus not explosions, but very fast fires. The burnt products of a deflagration move in the direction opposite to the combustion wave. An explosive deflagration produces an appreciable blast wave, with the potential to do damage. Explosives which normally deflagrate are termed propellents or low explosives.

Detonation • A detonation is caused by a very rapid chemical reaction which passes through the exploding material at speeds of 1 to 10km/sec,well in excess of sonic velocity. High presuures are developed, and the products of combustion move in the same direction as wave. A detonation is a shock wave accompanied by a chemical reaction. Explosives which normally detonate are termed high explosives.

Consequence of explosion • • • • • •

1. damage due to over pre-blast wave, shock wave 2. damage due to projectiles 3. thermal radiation 4. acoustic energy. Types of explosion 1. vapour cloud explosion-confined and unconfinedUVCE • 2.BLEVE • 3. Physical explosion- bursting of pressurized container. • 4. Dust explosion

Dust explosion • Explosion involving finely divided particles of solid materials are dissipated in air and ignited. • Eg: in flour mill, grain storage, coal industry, metallurgical industry etc. • An initial dust explosion can cause secondary explosion. The primary explosion send a shock wave through the plant, stirring up additional dust, possibly resulting in a secondary explosion.

Vapour cloud explosion • Sudden release of large quantity of flammable vapour • Dispersion of vapour through the plant while mixing with air • Ignition of resulting vapour cloud,

Energy of chemical explosion • The blast wave resulting from chemical reaction is generated by the rapid expansion of gases at the explosion site. The expansion can be caused by two mechanism • Thermal heating of reaction products • Change in the total number of moles by reaction.

Energy of physical explosion • Reaction does not occur and energy is obtained from the energy content of the contained substance. • Brodes equation. • E = ((P2-P1)V)/gamma-1

Modeling of explosion • TNT equivalence model • TNO model • Baker –strehlow method

Sources of ignition • • • • • • • •

Heating system Friction Hot surfaces Electricity Static electricity Internal combustion engine Tools smoking

Radiation • • • • • • •

Matter Elements Atoms Proton Neutron Electron isotopes

Types of radiation • • • • • •

Ionising radiation Non ionising radiation Particulate radiation Electromagnetic radiation Internal radiation External radiation

Ionizing radiation • Some nuclides are unstable and spontaneously change into other nuclides, emitting energy in the form of radiation, either particulate( alpha and beta) or electromagnetic. This property is called radioactivity. • Ionising radiation-alpha, beta, gamma, neutron, Xray • Non ionising radiation- UV,infrared ,Laser,Microwave.

• Alpha particle consist of two proton and two neutron, it is therefore heavy and doubly charged. Alpha radiation has a very short range and is stopped by a few cm of air, a sheet of paper. • The beta particle has mass and charge equal in magnitude to an electron. Beta radiation source outside the body may have more penetrating radiation . • Gamma and X-ray are all electromagnetic radiation similar in nature to ordinary light except that they are of much higher frequencies and energy.

Biological effects of ionizing radiation • • • • • • • • • •

Alterations in DNA, chromosomes, cells Genetic defects Cancer Hereditary damage Erythema (reddening of skin) Protection against external radiation1. Shielding- lead, concrete 2. Distance 3. Time Radiation monitoring- Geiger- muller tube (dose rate meters)

units quantity

Si unit

Old unt

Conversion factor

Absorbed dose

gray

rad

1gy=100 rad

Equivalent dose

sievert

rem

1Sv=100 rem

Radio activity

becquerel

curie

1Bq=2.7x10 -11

• Radioactivity- rate at which spontaneous decays occur. Bq corresponds to one spontaneous decay per second. • Absorbed dose- is the mean energy imparted by ionizing radiation to the mass of matter in a volume element.(J/Kg) • Equivalent dose- is the absorbed dose averaged over a tissue or organ multiplied by the relevant radiation weighting factor.(Biological damage) • Effective dose- is the sum of the equivalent dose to the exposed organs and tissues weighted by appropriate tissue weighting factor(sivert)

Non ionising radiation • • • • • • • •

Non ionising EM radiation. Longer wave length (lower energy) They do not cause ionisation in matter. UV (<400nm) Visible (400 to 700 nm) Infra red (>700) Microwave radiofrequency

Reaction hazards Run away reaction- the rates of most reaction increases rapidly with temp ,leading to the danger of their getting out of control, with large rise in temp and pre and loss of containment of the process material. - Reactivity with 02 - Reactivity with water - Self reacting compounds - Auto ignition hazards

The power of reactions • Possible violence of any reactions lies in the heat liberated, the temp that may be reached and the change in volume. • The heat of reaction is calculated from heats of formation of the reactants and products. • Equilibrium constant for the reaction at temp is governed by free energy change of the reaction.

Powerful inorganic reactions • Oxidation-reduction reactions • Acid-base reactions • Hydrations and hydrolysis

Hazardous organic reactions and processes • Exothermic reactions • Peroxide formation • Oxidation processes (liquid phase and vapour phase) • Halogenation processes • Nitration processes • A few other reactions can also be harmful if temperature control is lost

Reactivity as a process hazard • • • • •

Reactivity between reactants in process Reactivity with atmospheric oxygen Reactivity with water Self-reacting compounds ( mainly monomers) Reactivity with adventitious materials ( those which result from some incident involving loss of containment, which would increase its consequences.

Temp hazards • High temp hazards-increase blood circulation, increase heart rate, blood pre increases • Increase sweating-loss of salt and water • Digestive system-vomiting ,diarrhea • Fatigue • Leads to accident

HAZARDS IN THE PRESSURE SYSTEM FAILURE

• impact from the blast of an explosion or release of compressed liquid or gas • impact from parts of equipment that fail or any flying debris • contact with the released liquid or gas, such as steam and • fire resulting from the escape of flammable liquids or gases

Safety provision for pressure Vessels • Should be regularly tested and operated by trained operator • Temp, pre, flow rate should be regularly checked • Safety valve, vent valve, rupture disc should be provided • Release of toxic, flammable contents should be directed to scrubber

Hazard Rating of Process Plant • • • • •

Inventory analysis Dow F&EI Mond index(ICI) Toxicity index Chemical Exposure index (DOW)

INVENTORY ANALYSIS • Hold up quantities in the vessel associated with the process, intermediate and main storages • Quantities in pipe line • Examine the physical and chemical properties of materials for their major hazard potential. • Each inventory is evaluated based on its • - physical hazardous nature • - temp, pre and flash point • - auto ignition characteristics • -MAC value • - lethal value • - location

• Based on the threshold quantity of certain chemicals, the industry is declared as Major accident hazard unit (MAH Unit). • EG; LPG more than 50 T • All the MAH unit has to be prepared the Emergency plan, conduct mock drill.

Fire and Explosion Index • The Fire and Explosion Index (F&EI) calculation is a tool to help determine the areas of greatest loss potential in a particular process. It also enables one to predict the physical damage that would occur in the event of an incident. • • The first step in making the F&EI calculation requires using an efficient and logical procedure to determine which process units should be studied. A process unit is defined as any major item of process equipment. The following process units could be identified in a typical plant.

Dow index and Toxicity index • Fire and explosion index is a number which indicates the fire or explosion hazard of the particular unit. • Before hazard indexing can be applied the installation should be divided into logical independent elements or units • Determination of fire and explosion index(F) and toxicity index(T)

Steps in calculation of F&EI • • • • •

Divide the plant into units. The material factor for the unit MF Special material hazard factor General process hazard factor(GPH) Special process hazard factor.(SPH)

Material factor • This is a number generally from 1 to 60, which denotes the intensity of energy release from the hazardous material. For reactive material, the heat of reaction is used instead of heat of combustion. • MF= Net heat of combustion (KJ/Kg)/2326 • Special material hazard factor. • An additional percentage must be added to the MF of materials which have certain hazardous properties, provided these have not been taken into determining the MF.

Compound

MF

Acetone

12.3

Acetylene

20.7

Hydrogen

51.6

Isopropyl alcohol

13.1

Sulphur

4

Urea

3.9

Vinyl chloride

8

Special material hazards Special property of material

% to be added to MF

Oxidising

0 to 20

Reactive with water

0 to 30

Subject to spontaneous heating

30

Subject to spontaneous polymerization

50 to 75

Subject to explosive decomposition

125

Subject to detonation

150

Penalties for General process hazard • Exothermic reactions that generate self heat • Endothermic reactions – external heat source • Material handling and transfer-pumping and transfer lines. • Enclosed process units preventing dispersion of escaped vapours. • Access for emergency equipment – fire tenders etc. • Drainage of flammable materials.

Penalties for SPH • Toxic material which could impede the fire fighting. • Less than atm pressure operation with a risk of outside air entering. • Operation in or near flammable limits. • Dust explosion risks. • Higher than atm pressure. • Low temp operation with potential for embrittlement of carbon steel vessel.

• • • • •

Quality of flammable material. Corrosion and erosion of process unit operation. Leakage around joints and packing. Use of fired heaters. Hot oil heat exchange systems where hot oil is above its ignition temp. • Large rotating equipment including pumps and compressors.

• F=MF x (1+GPHtot) x (1+SPHtot) • MF=material factor, a measure for the potential energy of the dangerous substances present according to NFPA data • GPHtot = general process hazards, a measure for the hazards inherent in the process. • SPHtot = special process hazards, a measure for the hazard originating from the specific installation

• T = (Th +Ts)/100* (1+GPHtot+SPHtot) • Th = toxicity factor • Ts = suppliment for MAC value

• Determination of the toxicity index- toxicity index is based on the index figure for health hazards established by NFPA. • In addition , the toxicity factor has to be corrected for the MAC value of the toxic substance by adding to it a penalty Ts

NFPA index figure

Toxicity factor (Th)

0

0

1

50

2

125

3

250

4

325

MAC(ppm)

Penalty Ts

5

125

5-50

75

>50

50

Classification of hazard categories Fire and explosion index

Toxicity index

Category 1

F <65

T<6

Category 2

65
6
Category 3

F>95

T>10

Degree of Hazard for F&EI FEI INDEX RANGE DEGREE OF HAZARD

• • • • •

1 -60-Light 61 -96 – Moderate 97 -127 – Intermediate 128 – 158 – Heavy 159+ - Severe

Features dependent on F&EI unit • • • • • • • •

Fire protection of structural support Water spray protection of equipment and area. Special instrumentation Blowdown and spill control Combustible gas monitors Remote operation Building ventilation Explosion relief

• Your plant is considering the installation of a new rail car tank unloading facility. The facility will unload 25000gal tank cars containing either pure butadiene or cyclohexane. The unloading system equipped with an emergency shutdown system with remotely operated block valves. The unloading operation will be down by computer control. The rail cars are inerted with N2 to a pre of 40 psig, and the rail car relief system has a set pre of 75 psig. Combustible gas detectors will be located at the unloading station.

• . A deluge system will be installed at the unloading site with excellent water supply. A diking system will surround three sides of the facility with any spills directed to a covered impounding area. • Determine the Dow F&EI for this operation. • Butadiene =24 (MF) • Cyclohexane =16

Mond index • Mond index extends the calculation procedures of the Dow index to highlight particular hazards. Thus it provides separate indices for fire, internal explosion and aerial explosion potential as well as an overall hazard rating. • The first step is to divide the plant into units. • The next step is to determine the material factor B, which provides numerical base for the indices. • The base is then modified by many other considerations as follows.

• • • • • • •

1. Special material hazards M 2. Material factor B 3. General process hazards P 4. Special process hazards S 5. Quantity hazards Q 6. Layout hazards L 7. Acute health hazards T Or H

Calculation of indices • • • • •

Fire index (F) =B * K/N B= materil factor K= Material total in tonne N= working area in m2. 0-2 – Light, 5-10- moderate, 100-250extreme. • Fire index related to fire load.

Internal explosion index • A measure of the potential for explosion within the unit • E=1+(M+P+S)/100. • 0-1.5 – light • 2.5 -4 – moderate • Above 6 – very high

Aerial explosion index • Relates both to the risk and magnitude of a vapour cloud explosion originating from a release of flammable material. • A= B(1+M/100)(QHE/100)(T+273/300)(1+P) • 0-10- light • 30-100 – moderate • 100-400 – high • 400-1700- Very high

Over all hazard rating • Is used to compare units with diff types of hazards. • R= D(1+(0.2*E*(AF)^1/2)) • D=Dow index • 0-20- light • 100-500 moderate • 1100-2500 high • 2500 – 12500 very high • Over 12500 extreme.

Toxic incident Index • C=(T/100)(1+(M+P+S)/100)*Q • Equivalent Dow index :D=B(1+M/100)(1+P/100)(1+(S+Q+L+T)/100)

Industrial disasters • • • • •

Major disasters in chemical industry : Flixborough, Seveso, Mexico Bhopal etc.

Place

Year

Cause

1966

Approx. Loss of Life 18

Feyzin, France Flixborough, U.K. Mexico City, Mexico Bhopal, India

1974

51

1984

500

UVCE of Cyclohexane LPG: BLEVE

1984

2000

Release of MIC

Pasadena, USA Vizag, India

1989

23

1997

58

UVCE of Isobutane UVCE of LPG

LPG: BLEVE

FILXBOROUGH 1st June 1974 Cyclohexane TNT equivalent 32 tonnes Lethal Radius

125 meters

Causality Loss

28 $ 412 million (Rs.. 1854 Cr.)

Process Six reactors gravity circulation. Cyclohexane  Cyclohexanone and cyclohexanol. Oxidized (AIR) Operating Condition 8.8 Kg/Cm2 Pr. 155oC Temp. Exothermic reaction.

Nitrogen Controlled atmosphere - HighPr.N2 Storage Reactor pr. Maintained by off-gas venting SRV - Setting 11.0 Kg/Cm2

MEXICO DISASTER

19TH NOV 1984 leak in LPG Storage facility BLEVE OCCURED 500 Deaths Loss US$ 100 Millions

MEXICO CITY, 19.11.1984, MEXICO

“PHILLIPS” Pasadena Texas USA • 23rd Oct. 1989 • 23 Deaths 130 Injuries • Vapour Cloud explosion • Loss US$ 500 Millions

PASADENA, 23.10.1989, USA

FIRE & EXPLOSION IN HPCL REFINERY VIZAG • 7th Sept.1997 • Capacity - 6.5 million tons per annum • Facility for handling LPG

Vapour cloud Explosion involving LPG LOSS Rs. 256Cr.

Life Loss 58

The Flixborough disaster – 1 June 1974 • • • • •

• • • •

Cyclohexane oxidation plant A chain of 6 stirred reactors The agitator in reactor no.4 failed Reactor No.5 had to be taken out of line as a crack developed on it. Reactor 4 and 6 were connected by a make shift pipeline made in the form of a dog’s leg and two bellows ( by-pass assembly) Crack on the “by-pass assembly” Escape at sonic velocity of about 80 t of hot liquid cyclohexane at upto 155 deg c and 8 bar g This formed an enormous vapour cloud as big as a foot ball pitch. The vapour cloud exploded within a minute of the rupture.

The Flixborough disaster • The largest peace time explosion in Britain • Equivalent to over 30 t of TNT. • It wrecked the works and the main office block and damaged property within a radius of 5 km. • 28 persons working on the site, nearly all in the control room, were killed. • Hundreds of others, mostly, outside the site injured.

FILXBOROUGH, 01.06.1974, UK

The ‘Dioxin’ release at Seveso10 July 1976 • Reactor producing 2,3,5 trichlorophenol (TCP). • Rupture of a bursting disc fitted in the vent line of the reactor. • The bursting disc discharged a cloud of about 2 Kg of hot chemicals in to the open air. • A hot summer day with a light northerly breeze. • Heavy rain immediately after the discharge. • The content of the cloud was brought down to earth over a largely urban area.

Seveso • The cloud contained a small quantity (later estimated at 2 kg) of dioxin. • Dioxin (TCDD) • 2,3,7,8 tetrachlorodibenzoparadioxin. • The fatal dose of TCDD for an average person is less than 0.1 mg. • An area of about 10 sq.miles was contaminated, and by august at least 730 people had been evacuated. • Over 700 local inhabitants were affected by the poison and many animals died. • A considerable area of agricultural land was rendered unusable for many years.

Bhopal disaster – Dec.1984 • World’s worst industrial disaster. • Some 2500 people were killed and 100000 injured by the release of 26T of highly toxic methyl isocyanate (MIC) from Union Carbide’s insecticide formulation plant. • MIC – an intermediate in the manufacture of the insecticide carbaryl (trade name : Sevin) • Occupational Exposure limit of MIC : • 0.02 ppm or 0.05 mg/m3.

20,000 KILLED 170,000 SEVERELY AFFECTED

Bhopal Gas Tragedy – Dec. 2-3, 1984 And you thought only weapons could cause mass destruction

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Bhopal disater • •

Burial of an unknown child, Bhopal 198. This unknown child has become the icon of the world’s worst industrial disaster, caused by the U.S. chemical company, Union Carbide. PHOTO BY RAGHU RAI OF INDIA TODAY

Bhopal UC Sevin Plant

TANK 610

Flare Tower

Vent Gas Scrubber

MIC - Toxicity • The vapour is extremely toxic, attacking the skin and the mucous membrane of the eyes and the respiratory system.

MIC - Reactivity • Very reactive. • Polymerises readily in the presence of various catalysts including chlorides of iron to form the cyclic trimer, 1,3,5 – trimethyl isocyanurate. • Reacts with water to form CO2, methyl amine and other compounds. • Both reactions – highly exothermic. • Can become violent at higher temperatures and generate enough heat to vaporise most of the MIC

MIC process • Prodn of phosgene from chlorine, and carbon monoxide. • Prodn of methylcarbamoyl chloride from phosgene and monomethyl amine, using chloroform as a reaction solvent. • Pyrolysis of methylcarbamoyl chloride to form crude MIC. • Purification of crude MIC by fractional distillation in a plate column to remove chloroform and unconverted methylcarbamoyl chloride. • UCC’s specification for MIC included a max. chloroform content of 0.5 % ( but some times higher due to operational difficulties in the plate column.

Storage of MIC • MIC was stored in two horizontal stainless steel pressure vessels (604 grade) referred to as 610,611. • Each of 57 m3 nominal capacity. • Designed for full vacuum to 2.8 bar g. at 121 deg C. • The vessels were covered with earth mounds with concrete decks to protect against accidental impact, external fire, and for thermal insulation.

Storage of MIC – Safety features • A 30 ton refrigeration system with a heat exchanger through which MIC was circulated was provided to maintain its storage temperature at 0 deg.C or lower, in order to minimise polymerisation. • Instrumentation for each MIC storage vessel included : • A temperature indicator and high-level alarm. • A pressure indicator / controller to regulate the pressure by admitting nitrogen or venting vapour to the vent gas scrubber (VGS) or flare. • A liquid level indicator / alarm for high and low level.

Possible reasons for Bhopal disaster • A run away reaction in the storage tank 610 due to contamination with catalytic materials and water. • The contents were not sampled regularly to monitor contamination. • Polymerisation and reaction with water. • The refrigeration system was not working. • Corrosion of the storage vessels. • Failure of the caustic circulation in the VGS. • Release of MIC and other vapours through the flare without being burnt. • Negligence on the part of the management to maintain the safety systems. Cost reduction measures. • Operation of the plant by inexperienced people.

Do you need any intro to these pictures?

The massive blaze at the IOC Terminal, Sitapura Industrial Estate in Jaipur on 30 Oct 2009 CISRA

 Petro products worth Rs.1400 to 1500 million were burnt  11 Died and more than 100 injured  Indian army troops are still at work  The neighboring units are damaged  Unable to put off the raging Fire the products are allowed to burn

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October 30, 2009 Friday (The Hindu) More than 17 hrs of the fire broke out the fire fighting is yet to start The fire that started due to a leakage in one of the valves at around 1930 hrs on Thursday continues to rage in five of the 13 tanks that stored petrol, diesel and kerosene. ‘There is not much we can do currently. We have to allow all the petrol and diesel to burn, before fire tenders can go anywhere near the burning tanks’ – Minister 2 diesel tanks of 20,000klof autofuel and 3 petrol tanks of 20,000kl capacity will have to burn before the fire tenders arrive from Mathura, Panipet and Ahmedabad

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What Went Wrong? Still unanswered Questions  Why no detection about the major leak has been made?

 Why no immediate action has been taken to either arrest the leak or alert the staff?  Why no HC detectors ?  What is the source of ignition?  Why there is a lack of fire water supply?  What happened to the Emergency Plan?

CISRA

PHYSICAL PROTECTION •Strict & Rigorous approach in following the Relevant Standards , Codes & Practices •Built in Safety Devices and Safety System •Venting through Tall stacks •Field Monitors for Different Toxic Gases •Burning Waste gases in a Flare System

•Provision of Wind Cones •Fire Proofing of Steel Structures •Passive Protection System

•Active Protection system •Automatic Protection system

1 0 •Improved Waste Water Management 2

EDUCATIONAL PROTECTION •Periodic Training Programme on Safety, Fire Safety and Hazardous properties of materials •Mock Fire Drill •Safety Manuals •Health & Safety News Bulletins •Safety Motivation schemes •Plant Operating Manual •Educating the Public Living nearby about the activities in the industry

THANK YOU