Information Technology in Risk Assessment Deaconu Lucia ERSM 1

7/28/2019 Information Technology in Risk Assessment Deaconu Lucia ERSM 1

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Information Technology in Risk Assessment

- Subject 3 -

Deaconu Lucia-Timea

ERSM 1

Determine and plot the physical effects and individual risk curves based on the following

information:

benzene chemical accident due to leakage from a tank

storage in a spherical tank, volume 50 cu m

tank filled at 80% with a liquid stored at room temperature

rectangular hole 10 x 1 cm, at the bottom of the tank

tank is located in a concrete retention vat, area 50 sq m

atmospheric data:

wind speed of 2 m/s from the S direction, measured at 10 m height from the

ground

outdoor temperature is 15 C

100% sky covered with clouds

inversion at 1,500 m

humidity 70%

urban areas.

Consider:

high mortality area: c> 1,000 ppm

irreversible damage area: c> 500 ppm

What is the concentration c at a distance of 500 m downwind from the release source?

Determine the societal risk considering two scenarios, at the source location:

464701,69N i 233242,55E.


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1. General presentation of the substancebenzene

NFPA 704:

Red 3 -- Flammability: Ignites at normal temperatures

Blue 1 -- Health Hazard: Slightly hazardous

Yellow 0 -- Reactivity: Normally stable

Air & Water Reactions

Highly flammable. Slightly soluble in water.

Fire Hazard

Behavior in Fire: Vapor is heavier than air and may travel considerable distance to a source of

ignition and flash back.

Health Hazard

Dizziness, excitation, pallor, followed by flushing, weakness, headache, breathlessness, chest

constriction, nausea, and vomiting. Coma and possible death.

Hazards Chemical Name: BENZENE Molecular Formula: C6H6 Molecular Weight: 78.11 g/mol Ambient Boiling Point: 78.8 C Freezing Point: 5.5 C Lower Explosive Limit: 1.4 % Upper Explosive Limit: 8.0 % AEGL-1 (60 min): 52 ppm AEGL-2 (60 min): 800 ppm AEGL-3 (60 min): 4000 ppm IDLH: 500 ppm LEL: 12000 ppm

Figure 1.NFPA Rating Explanation Guide

A clear colorless liquid with a petroleum-like odor, it

belongs to the Hydrocarbons and Aromatics Reactive Groups.

Flash point is less than -17.77 C. Less dense than water and

slightly soluble in water. Hence floats on water. Vapors are

heavier than air (cameochemicals.noaa.gov/).


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UEL: 80000 ppm2. Protection and first aid in case of exposure

Firefighting

Do not extinguish fire unless flow can be stopped. Use water in flooding quantities as

fog. Solid streams of water may spread fire. Cool all affected containers with flooding quantities

of water. Apply water from as far a distance as possible. Use foam, dry chemical, or carbon

dioxide (cameochemicals.noaa.gov/).

Non-Fire Response

Keep sparks, flames, and other sources of ignition away. Keep material out of water

sources and sewers. Build dikes to contain flow as necessary. Attempt to stop leak if without

undue personnel hazard. Use water spray to knock-down vapors (cameochemicals.noaa.gov/).

Protective Clothing

Skin: Wear appropriate personal protective clothing to prevent skin contact.

Eyes: Wear appropriate eye protection to prevent eye contact.

Wash skin: The worker should immediately wash the skin when it becomes contaminated.

Remove: Work clothing that becomes wet should be immediately removed due to its

flammability hazard.

Change: No recommendation is made specifying the need for the worker to change

clothing after the work shift (cameochemicals.noaa.gov/).First Aid

Eyes: First check the victim for contact lenses and remove if present. Flush victim's eyes

with water or normal saline solution for 20 to 30 minutes while simultaneously calling a hospital

or poison control center. Do not put any ointments, oils, or medication in the victim's eyes

without specific instructions from a physician. Immediately transport the victim after flushing

eyes to a hospital even if no symptoms (such as redness or irritation) develop.

Skin: Immediately flood affected skin with water while removing and isolating all

contaminated clothing. Gently wash all affected skin areas thoroughly with soap and water.

Immediately call a hospital or poison control center even if no symptoms (such as redness or

irritation) develop. Immediately transport the victim to a hospital for treatment after washing the

affected areas.


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Inhalation: Immediately leave the contaminated area; take deep breaths of fresh air.

Immediately call a physician and be prepared to transport the victim to a hospital even if no

symptoms (such as wheezing, coughing, shortness of breath, or burning in the mouth, throat, or

chest) develop. Provide proper respiratory protection to rescuers entering an unknown

atmosphere.

Ingestion: Do Not Induce Vomiting! Volatile chemicals have a high risk of being

aspirated into the victim's lungs during vomiting which increases the medical problems. If the

victim is conscious and not convulsing, give 1 or 2 glasses of water to dilute the chemical and

immediately call a hospital or poison control center. Immediately transport the victim to a

hospital. If the victim is convulsing or unconscious, do not give anything by mouth, ensure that

the victim's airway is open and lay the victim on his/her side with the head lower than the body.

Other: Since this chemical is a known or suspected carcinogen you should contact a

physician for advice regarding the possible long term health effects and potential

recommendation for medical monitoring. Recommendations from the physician will depend

upon the specific compound, its chemical, physical and toxicity properties, the exposure level,

length of exposure, and the route of exposure (cameochemicals.noaa.gov/).

3. Methods of obtaining the resultsa)

CAMEO Chemicals

CAMEO is a suite of software programs used to plan for and respond to chemical

emergencies. It was developed for chemical emergency planners and responders by the CAMEO

team. CAMEO includes a set of databases, or modules, a toxic gas dispersion model (plume model)

called ALOHA, and an electronic mapping program called MARPLOT (US EPA, 2004).

b) ALOHAALOHA (Areal Locations of Hazardous Atmospheres) is a computer program designed

especially for use by people responding to chemical releases, as well as for emergency planning

and training. ALOHA models key hazardstoxicity, flammability, thermal radiation (heat), and

overpressure (explosion blast force)related to chemical releases that result in toxic gas

dispersions, fires, and/or explosions.

ALOHA models three hazard categories: toxic gas dispersion, fires, and explosions.

ALOHA employs several different models, including an air dispersion model that it uses to


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estimate the movement and dispersion of chemical gas clouds. From this model, ALOHA is able

to estimate the toxic gas dispersion, the overpressure values from a vapor cloud explosion, or the

flammable areas of a vapor cloud. ALOHA uses additional models to estimate the hazards

associated with other fires and explosions. ALOHA can solve problems rapidly and provide

results in a graphic, easy-to-use format. This can be helpful during an emergency response or

planning for such a response (US EPA, 2006).

c) RISKCURVESRiskcurves is a specialized software package designed to calculate Individual Risks and

Group Risks (GR) resulting from an accidental release of flammable, explosive or toxic

substances. By providing an intuitive user-interface the package guides the user in the calculation

procedure.

A Quantitative Risk Assessment (QRA) analyses the risks of accidents involving with

dangerous substances, resulting in lethal victims, injuries and/or material damage to

surroundings. In order to be able to compare risks, quantitative values are given for Individual

Risks and Societal Risk (TNO, 2007).

4. ResultsTaking into account the projects requirements, only the discharge and dispersion

scenario was analyzed. In this case scenario, where a hole at the bottom of the tank releasesbenzene in a retention vat and the chemical is not burning but is forming an evaporating puddle,

ALOHA program is used to calculate the physical effects, respectively benzene dispersion.

As can be seen from figure 2, the location of the tank is in an industrial area, near the

periphery of Cluj-Napoca city at approximately 400 meters from where the urban area begins.


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Figure 2.Location of the tank (Source: maps.google.com)

After introducing the data, the ALOHA program calculates the source strength to see the

amount of benzene released, the release rate and the diameter of the puddle, limiting the release

duration to 1 hour.


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To calculate the threat zone (the physical effects), we must select the toxic level of

concern (LOC). In this case, for red threat zone the LOC it is considered 1000 ppm concentration

(high mortality), and for orange threat zone the value of the LOC is 500 ppm (intoxications).

After this inputs, the program calculates, using the Gaussian model run, the distances

where this levels of concern are exceeded.

At a distance under 10 meters from the source, the benzene concentration can have a

lethal effect on humans, depending on the exposure duration, and between 10 and 14 meters it

can cause acute intoxications.

Due to the errors caused by short distance predictions and the near-field heterogeneity,ALOHA is not able to draw the lines corresponding to the levels of concern (1000 ppm and 500

ppm).

Downwind from the release source at 500 meters (the point of interest is the urban area)

the concentration of benzene in the atmosphere is 1.48 ppm (Figure 3). This concentration is

very low and it has no effect on human health.


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Figure 3.Downwind concentration at 500 meters

In order to establish the Individual Risk the probability of death of a person at a given exposure

from toxic dispersion must be calculated. This probability uses the Probit function. The relation

between the probability of death of an effect, P, and the corresponding probit, Pr, is given by

(Uijt de Haag & Ale,2005):

( )

The probability of death due to exposure to a toxic cloud is calculated with the use of a

probit function that has the following relation:

where:

Pr -probit corresponding to the probability of death (-)

a, b, n -constants describing the toxicity of a substance (-)

C -concentration (ppm or mg m-3

)

t -exposure time (minutes)


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The constants describing the toxicity of a substance a, b and n for benzene have the

following values (American Institute of Chemical Engineers, 2000):

a= -109.7

b=5.3

n=2

The conversion of concentration from ppm in mg/m3

is realized using the following

formula:

M benzene = 78.11 kg/kmol

In table 1 is calculated the Probit value and the Probability of death, using the

concentration in ppm and the exposure time in minutes. The values of distance [m], time [min]

and concentration [ppm] are taken from ALOHA program.

Due to the atmospheric data used as input and the fact that the benzene dispersion is from

pool evaporation, the concentration in the atmosphere is low and has no significant effects upon

human health. Even in the range of the pool (4 meters) the Probability of Death is 3.55E-06,

which means that the probability of death is insignificant.

Figure 4.Probability of death in pool evaporationbenzene dispersion


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Table 1.Calculating the Probability of Death

At 500 meters, a 1.48 ppm concentration and a value of Probit function of -83.8443, the

Probability of Death is zero.To complete the exposure and effects determination from the release and dispersion of a

dangerous substance (benzene) in the environment upon humans health, the Societal Risk is

calculated using the RiskCurves program.


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After we define the input data in the program, in order to perform Societal Risk

calculations (f-N curve) we have to edit the population grid for day and for night time, as

following:

Figure 5.Grid with population in day time

Figure 6.Grid with population in night time

Because the area where the vessel is located is an industrial one, on day time the density

of the population is higher than in the night time. We have to consider these differences to


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minimize the errors in calculation and to have a better understanding on the Societal Risk in case

of an accident.

Further are analyzed two scenarios: one is toxic dispersion of benzene from pool

evaporation, and the other is pool fire due to benzene accidental release in the retention vat. The

data inputted in these models are taken from ALOHA program and from the failure rates

database (HSE, 2012).

Figure 7.Input data for Benzene toxic dispersion

Figure 8.Input data for Benzene pool fire

After these data are analyzed and the program ends all the calculation, the results are

presented for each scenario.

The f-X curve (Individual Risk) for benzene dispersion is not represented because the

risk of this scenario is zero.


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Figure 11.Pool fire risk contours

These contours represent the Individual risk of death: the unacceptable limit is 1e-5 y-1

and the acceptable limit is 1e-6 y-1

(Trbojevic, 2010).

As explained before, the toxic dispersion of benzene has zero risk, so these contours are

representative only for pool fire effects.

Figure 12.Pool fire physical effects


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In figure 12 is presented the physical effects of thermal radiation from the benzene pool

fire. As can be seen, these effects have a local impact, with no implications and damages upon

other buildings. The impact upon human health is also insignificant; only for people located in

the range of these contours we can talk about risks of intoxications, burns or mortality.

5. DiscussionsIn the first scenario - toxic benzene dispersion, due to atmospheric data (like stability

class D, wind speed, humidity) and installation characteristics (especially the holes diameter in

the vessel and the diameter of the retention vat), the results of the simulations (in ALOHA and

Riskcurves) show low values for concentrations in the atmosphere, with minor impact upon

human health. The physical effect concentration of benzene in the atmosphere results in

insigni fi cant ri sksto human health, so there are small individual r isksand societal r isks.

The second scenario presents the effects of a pool fire resulted from an accidental leakage

from the vessel in the retention vat. Although the flow rate is small and the total mass released in

one hour is 158 kg, the physical effects (thermal radiation) can be taken into account at a local

scale (range of 20 m). The thermal radiation can have a lethal impact upon humans, or it can

produce 1st, 2

ndor 3

rddegree burns.

Besides possible errors in calculation due to the quality of the input data, we must take

into account also the limitations of the software used. For example, ALOHA has limited the

release duration to maximum one hour.

6. ConclusionsIn conclusion one can state that using ALOHA, Microsoft Excel and Riskcurves

programs, we can determine the effects that a certain accident has on the environment and on the

population, by calculating the Individual Risk (depending on the probability of death) and the

Societal Risk (depending on the number of deaths).


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Information Technology in Risk Assessment Deaconu Lucia ERSM 1