MOND’S TOXICITY INDEX

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JITHIN.K.JOSE B090311CHNIRMAL.A B090540CHRAHUL SREEKUMAR B090995CHVISHNU VENUGOPAL B090369CH

NEED FOR AN INDEX

To get an approximate yet workable assessment of risk at much lesser costs, indices have been developed which link typical findings of elaborate risk analysis to scales of risk.

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NEED FOR A TOXICITY INDEX

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Many possible effects, both chronic and acute.There are several different routes of exposure length of exposure frequency important Individuals may differ markedly in response to a particular dose. There is often difficulty in getting an agreed dose- response relationship for humans, Therefore, the task of constructing a meaningful toxicity index is formidable

BASIS FOR THE TOXICITY INDEX

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The inhalation route was selected as the basis for assessing toxic hazard potential.

Skin effects, either absorptive, corrosive, or scalding, can be very severe but are usually confined to a very short distance from a release point, whereas inhalation effects may be important over a considerably greater range and may extend off-site.

In a fully quantitative analysis, the area

affected by the release would be estimated

How to Rank the Hazards?

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Two indices are mainly used for the ranking of hazards.

Dow Index and the Mond Index, used for

• Systematically identifying hazards

• Providing a method of ranking priorities

The Dow Index was originally developed by the Dow Chemical

Company to assist in the selection of fire protection methods.

The Mond Index was developed by ICI for the chemical industry, after

the Flixborough disaster. It expands on the Dow Index

MOND’S TOXICITY INDEX

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•The monds toxicity index was developed from dow F and

dow E index by personnel at the ICI Mond division.

•This edition (1973) was extended to cover a wider range of

process and storage installations.

•Also included was a procedure to allow for the effects of

good design, and of control and safety instrumentation.

MOND’S TOXICITY INDEX

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PROCEDURE

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PREVENTIVE MEASURESThey fall into 2 categories:

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IMPLEMENTATION

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STAGES OF DETERMINING THE TOXICITY INDEX

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Dividing the plant into units

• The process of division into units should match changes of

process conditions or operations within the overall plant

• It is important not to mask units of high potential by including

them within a large section with materials of lower toxicity so

that a low toxicity factor is used in the index

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Estimating the rate of vapor generation

• For all conditions, there are standard formulas or procedures

for quantitative estimation, and computer programs are

available for the calculations. Examples of such programs are

Whazan (Technica), Chems-Plus (Arthur D. Little).

• To make the estimate, the physical properties of the material

are needed in addition to the conditions at the release point.

These will include the size and shape of the release orifice

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• External conditions may affect the vapor generation

rate, for example, when a cold liquid is spilled and

the vapor generation rate depends on the area

covered and the rate of heat flow from the ground

into the spilt material

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Selecting the toxic concentration

• The basis of the 5-min period is that in an incident, it can be expected that within that time a worker on a chemical plant or process would either have escaped from the affected area or have donned protective equipment

• the basis for various limits, when available as Toxicity Reviews should be consulted because the required information for a tolerable level for a single short exposure may be provided.

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Calculating the base factor T from Q and X

• to relate T to the area within which the chosen limiting concentration would be exceeded.

• a measure of the area potentially at risk from a release from a particular unit is the ratio (Q/X) of the rate of vapor generation (Q) and the toxic concentration (X)

• T = 2 /(Q/X) - 3

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Allocating penalty factors for material, process, and layout

features• Material properties: penalty factor M.• General process features: penalty factor P.

This is intended to allow for features of the plant and process that may affect the likelihood of a release or its magnitude

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• Special process factors: penalty factor S. This section is intended to make allowance for features such as extremes of temperature or pressure because these make loss of containment more likely or more difficult to control. Material strength, corrosion, and erosion effects, as well as vibration and load cycling, are included here. In addition, material properties relating to flammability and any special operati ng conditions, L (e.g., closeness to the flammable region) are covered

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Determining the final index value

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Toxicity index = T[l + (M/100)][1+ P/100)] [1 + (S/100)+(L/100)]

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Mond IndicesMond Indices

Fire & Explosion index :(F & E1) = MF x (GPH) (SPH)

Toxicity Index : Th + Ts (1+GPH+SPH) 100

Where, MF = Material Factor

SPH = Special Process Hazard

GPH = General Process Hazard

Th = Toxicity factor based on the NFPA hazard index (0 – 4)

Ts = Correction factor (additional penalty) for toxicity based on Maximum Allowable Concentration (MAC) value in ppm

GPH includes processes e.g. exothermic reaction,

endothermic reactions, hydrogenation, alkylation,

isomerisation, sulphurization, neutralization,

esterification, oxidation, polymerization,

condensation, halogenation, nitration, loading-

unloading operation, enclosed process units,

inadequate drainage and proper access etc.

different penalties are assigned for different

processes.

General Process Hazard (GPH)

Process Hazard Process Hazard ManagementManagement

SPH includes special hazards posed due to

process parameters like temp., pressure,

flammability ranges (UEL, LEL) of material and

issues like internal and external corrosion, leakage

from joints etc. additional penalties are assigned

for special process hazards. Selection of the

process units which may contribute to a fire or

explosion or toxic release

Special Process Hazard (SPH)

Process Hazard Process Hazard ManagementManagement

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Toxicity Factors and Correction Factor for MAC values

NFPA Index Number

Toxicity Factory(Th)

0 0

1 50

2 125

3 250

4 325

MAC (in ppm) TS

5 and blow 125

Between 5 and 50 75

50 and more 50

Risk AnalysisRisk AnalysisGeneral Principles of Risk Analysis

1. All relevant risks are systematically addressed Identify major, don’t concentrate on minor Consider those aspects of work which are

hazardous Take into account & critically assess existing safety

controls & measures provided

2. Address what actually happens Actual practice, not instruction Consider non-routine operations Pay attention to changes/interruptions

Risk AnalysisRisk AnalysisGeneral Principles of Risk Analysis

3. Include all who could be affected, including visitors, contractors, and general public

4. Take into account, and objectively assess, control measures

5. The level of protection measures should match the level of risk (i.e. risk within the ALARP region)

6. In most cases, make a rough assessment first, find out the need for detailed assessment and carry out the same, if needed.

Indices and the Extent of Hazard

Dow F & E index

Mond’sToxicity Index

Degree of Hazard

1 – 60 1 – 6 Light

61 – 96 6 – 10 Moderate

97 – 127 > 10 Intermediate

128 – 158 > 10 Heavy

> 159 > 10 Severe

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