Consequence Consequence AnalysisAnalysis

Dr. AA

Department of Chemical Engineering

University Teknology Malaysia

Consequence AnalysisConsequence Analysis

• Determine the amount / rate of release– Source modelling

• Model the dispersion• Effect of Chemicals released

– Toxic Effect– Fire– Explosion

• Estimate Fatality : Probit• Estimate injury / health effect

– Heat Effect / Toxic Effect

• Estimate Losses

Hazard Modelling

Estimation of Estimation of FatalityFatality

(Probit Analysis)(Probit Analysis)

Estimation of Fatality: Probit Estimation of Fatality: Probit AnalysisAnalysis

• The dose level of the various hazard events against fatality can be conveniently determined using Probit Analysis.

• It is a graphical and Look-up Table approach to determine probability of fatality

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Probit AnalysisProbit Analysis

• The probit variable Y is computed from:

Y = k1 + k2 ln V

• Values of constants k1, k2 and causative variable V (representing the dose) are given in table

• Once the probit is obtained, it can be converted into % fatality

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Probit: Toxic ReleaseProbit: Toxic Release

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Causative variable, V = CaT (C is concentration in ppm, T is time in minutes)

Probit Parameters

Type of Injury a K1 K2Ammonia Death 2.0 -35.9 1.85Carbon Monoxide Death 1.0 -37.98 3.7Chlorine Death 2.0 -8.29 0.92Ethylene Oxide Death 1.0 -6.19 1.0Hydrogen Chloride Death 1.0 -16.85 2.0Nitrogen Dioxide Death 2.0 -13.79 1.4Phosgene Death 1.0 -19.27 3.69Propylene Oxide Death 2.0 -7.42 0.51Sulfur Dioxide Death 1.0 -15.67 1.0Toluene 2.5 -6.79 0.41

Probit: Fire and ExplosionProbit: Fire and ExplosionType of injury or damage Causative variable

(V)

Probit parameters

k1 k2

Fire

Burn deaths from flash fire

Burn deaths from pool burning

Explosion

Deaths from lung haemorrhage

Eardrum ruptures

Deaths from impact

Injuries from impact

Injuries from flying fragments

Structural damages

Glass breakage

po

po

J

J

J

p0

p0

-14.9

-14.9

-77.1

-15.6

-46.1

-39.1

-27.1

-23.8

-18.1

2.56

2.56

6.91

1.93

4.82

4.45

4.26

2.92

2.79

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Here, te is the effective time duration (s), t is the time duration of pool burning (sec), Ie is the effective radiation intensity (W/m2), I is the radiation intensity from pool burning (W/m2), te is the effective time duration (s), po is peak overpressure (N/m2), J is impulse (Ns/m2), C is concentration (ppm) and T is time interval (min).

teIe4 / 3 /104

t Ie4 / 3 /104

Conversion of Probit to Fatality dataConversion of Probit to Fatality data

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% 0 1 2 3 4 5 6 7 8 9

0 - 2.67 2.95 3.12 3.25 3.36 3.45 3.52 3.59 3.66

10 3.72 3.77 3.82 3.87 3.92 3.96 4.01 4.05 4.08 4.12

20 4.16 4.19 4.23 4.26 4.29 4.33 4.36 4.39 4.42 4.45

30 4.48 4.50 4.53 4.56 4.59 4.61 4.64 4.67 4.69 4.72

40 4.75 4.77 4.80 4.82 4.85 4.87 4.90 4.92 4.95 4.97

50 5.00 5.03 5.05 5.08 5.10 5.13 5.15 5.18 5.20 5.23

60 5.25 5.28 5.31 5.33 5.36 5.39 5.41 5.44 5.47 5.50

70 5.52 5.55 5.58 5.61 5.64 5.67 5.71 5.74 5.77 5.81

80 5.84 5.88 5.92 5.95 5.99 6.04 6.08 6.13 6.18 6.23

90 6.28 6.34 6.41 6.48 6.55 6.64 6.75 6.88 7.05 7.33

% 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9

99 7.33 7.37 7.41 7.46 7.51 7.58 7.65 7.75 7.88 8.09

Heat Effect Heat Effect CriteriaCriteria

Thermal Burn Injury Criteria (FEMA, 1990)Thermal Burn Injury Criteria (FEMA, 1990)

Radiation Intensity

Time for severe pain (sec)

Time for second degree burn (sec)

1 115 663

2 45 187

3 27 92

4 18 57

5 13 40

6 11 30

8 7 20

10 5 14

12 4 11

Permissible Thermal Radiation Exposure for Flares Permissible Thermal Radiation Exposure for Flares from API 521 (1997)from API 521 (1997)

Thermal Radiation Intensity (kW/m2)

Type of Damage

1.6 Permissible level at any location where some personnel are continuously exposed

4.7 Permissible level in areas where emergency actions lasting several minutes may be required by

personnel without shielding but with appropriate clothing

6.3 Permissible level in areas where emergency actions lasting up to 1 minute may be required by personnel

without shielding but with appropriate clothing

9.5 Permissible level in areas where exposure to personnel is limited to a few seconds, sufficient for

escape only

Thermal Dose for exposure to fireballThermal Dose for exposure to fireball

Thermal Dose(kJ/m2)

Type of Injury

40 Threshold of pain

100 Sunburn (first degree burn)

150 Blisters (Second-degree burn)

250 1 % fatal (third degree burn)

500 50 % fatal (third degree burn)

1200 99 % fatal (third degree burn)

Effect of Thermal Radiation on Structures Effect of Thermal Radiation on Structures TNO, 1992TNO, 1992

Type of Damage Damage Level 1(radiation intensity,

kW/m2)

Damage Level 2(radiation intensity,

kW/m2)

Steel 100 25

Wood 15 2

Synthetic Materials

15 2

Glass 4 -

Damage Level 1 – Surfaces of exposed materials catch fire and structural elements collapse or rupture

Damage Level 2 - Surfaces of exposed experience serious decoloration as well as peeling and structural elements undergo substantial deformation

Thermal Radiation Limits on Structure (Lees, 1996)Thermal Radiation Limits on Structure (Lees, 1996)Radiation intensity

(kW/m2)Limit Description(BS5908, 1990)

37.5 Intensity at which damage is caused to process equipment

25 Intensity at which nonpiloted ignition of wood occurs

12.5 Intensity at which piloted ignition of wood occurs

Radiation intensity (kW/m2)

Limit Description(Design Guidance by Dinneno, 1982)

30 Spontaneous ignition of wood

20 Ignition of No 2 fuel oil in 40 seconds

10 Ignition of No 2 fuel oil in 120 second

18-20 Cable insulation degrades

12 Plastic melts

37.5 Equipment damage

9 Equip. damage (conservative value used in flare design)

Toxic Effect Toxic Effect CriteriaCriteria

Toxic Effect CriteriaToxic Effect Criteria

• What Concentration are considered dangerous?

– PEL, TLV etc designed for workers are overly conservative – designed for long-term exposure, not for short-term, emergency condition

• Some guidelines

– AIHA: ERPG - Emergency Response Planning Guideline

– NIOSH: IDLH

– Nat Acad Sci : EEGL (emergency exposure guidance level) and SPGEL(short term public emergency guidane)

– TLV, PEL etc

• For design of ERP, the ERPG, SPEGL, EEGL are more directly relevant for general public

ERPG ERPG (see pp201-202 Crowl & Louvar)(see pp201-202 Crowl & Louvar)

• ERPG-1– Max airborne concentration below which it is believed nearly

all individuals could be exposed for up to 1 hour without experiencing effect other than mild transient adverse health effect or perceiving a clearly defined objectionable odor.

• ERPG-2– … without experiencing or developing irreversible or other

serious health effects or symptoms that could impair their ability to take protective action

• ERPG-3– … without experiencing or developing life threatening health

effects (similar to EEGL)

• Sometimes called TEEL– Example : Ammonia - ERPG 1,2,3 = 25,200,1000 ppm

ERPG (Selected Chemicals)ERPG (Selected Chemicals)Chemical ERPG1 (ppm) ERPG2 (ppm) ERPG3 (ppm)

Acrylic Acid 2 50 750

Ammonia 25 200 1000

Benzene 50 150 1000

Chlorine 1 3 20

Formaldehyde 1 10 25

Methanol 200 1000 5000

Methyl Isocyanate

0.025 0.5 5

Phenol 10 50 200

Styrene 50 250 1000

Sulfur dioxide 0.3 3 15

Toluene 50 300 1000

Vinyl acetate 5 75 500

EEGLEEGL

• EEGL – Emergency Exposure Guidance Level

– Defined as concentration of gas, vapour aerosol that is judged acceptable and that allows exposed individuals to perform specific tasks during emergency condition lasting from 1 to 24 hours.

• National Research Council committee on Toxicology (USA) has submitted EEGL for 44 chemicals.

• NERC also developed SPEGL (Shor term public emergency guidance)

– Defined as acceptable concentration for exposure for members of general public

– Generally SPGEL is 10-50% of EEGL

SOME EEGLSOME EEGLChemicals 1 hour EEGL 24 hour EEGLAcetone 8500 1000

Ammonia 100Benzene 1 0.1

Carbon Monoxide 400 50Chlorine 3 0.5

Chloroform 100 30Methane 5000Methanol 200 10

Nitrogen dioxide 1 (SPEGL) 0.04 (SPEGL)Sulfur dioxide 10 5

Xylene 200 100

IDLHIDLH

• IDLH by NIOSH

• Concentration for acute toxicitymeasures for common industrial gas

• Defined as a condition “ that poses a threat of exposure to airborne contaminants when that exposure is likely to cause death or immediate or delayed permanent adverse health effect or prevent escape from such an environment”.

• Considered as a maximum concentration above which only a highly reliable breathing apparatus providing maximum protection is permitted.

Toxic End PointToxic End Point

• EPA promulgamated a set of toxic end points to be used for air dispersion modeling for toxic gas releases as part of EPA RMP

• Toxic end points follows (in order of preference)

– ERPG-2

– LOC (level of concern) - the maximum concentration of an extremely hazardous substance in air that will not cause serious irreversible health effects in the general population when exposed to the substance for relatively short period.

Recommended Hierarchy of alternative Recommended Hierarchy of alternative concentration guidelinesconcentration guidelines

Primary Guideline

Hierarchy of alternative guidelines

Source

ERPG1EEGL (30 minute)

IDLH

AIHANRC

NIOSH

ERPG2EEGL (60 minutes)

LOCPEL-CTLV-C

5 X TLV-TWA

AIHANRC

EPA/FEMA/DOTOSHAACGIHACGIH

ERPG3PEL-STELTLV-STEL

3 X TLV-TWA

AIHAOSHAACGIHACGIH