skc5173 week 6b mond index

8/13/2019 Skc5173 Week 6b Mond Index

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Prepared by

Associate Prof. Dr. Mohamad Wijayanuddin Ali Chemical Engineering DepartmentUniversiti Teknologi Malaysia


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Mond Index - Introduction Rapid hazard assessment method for use on chemical plant or in

plant design. It is numerical ranking for each section of the plant based upon

properties of materials present, quantity, operating conditions andtypes of process.

Developed by the ICI Mond Division. Uses of the index include assessment of operational plants and theinitial examination of new design (an aid to inherently safe design).

If used early in the design phase, it can help identify featuresrequiring more detailed study by techniques such as HAZOP.

Assessment best carried out by a team consisting of personnel

familiar with the plant and process, as well as experience in usingthe index.


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Mond Index

Objectives of Mond Index

To Identify, Assess and Minimize potential hazards on chemical plants units for new andexisting processes

About Mond Index

Index primarily concerned with fire and explosion problem.

Toxicity is considered only as possible complicating factor.

Method gives credits for plant safety features (both hardware and software).


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Mond Index Procedures

Plant is divided into a number of units and each unit is assessed individually

3 stages analysis for each unit :-

1) Consider unit in basic form with minimum controls required for normal operation -worst case assessment

2) Review factors to reduce original indices

3) Offsetting - hazard reduction trying to decrease number and size of potential accidents


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It is often best to carry out first stage analysis for all units. be conservative in assigning values, then review higher score for possibility of reducing.

1) Need to select key material present in the unit.

Key material is the most dangerous chemicals (inherent properties), which higher possibility

for combustion, explosion or exothermic reaction.

2) Calculation of Material Factor, B

3) Special Material hazards, M

4) Special Process hazards, S

5) Quantity Hazards, Q



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6) Layout Hazards, L

7) Acute Health Hazards, T

8) Calculation of Indices - Dow Index (D), Fire Index (F), Internal Explosion Index (E),

Overall Hazard Rating (R).

The most important is R.

Experience from applying full method, uncommon for R above HIGH(2)



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Mond Index - Criteria

The most important criteria - overall hazard rating, R

Overall Hazard Rating Category

0-20 Mild

20-100 Low100-500 Moderate

500-1100 High (group 1)

1100-2500 High (group 2)

2500-12,500 Very high

12,500-65,0000 Extreme

> 65,000 Very extreme


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Offsetting Measures

1) Try to decrease number of accidents containment- use high design standards for pressure vessels, storage tanks, transferpipelines, bunds, leak detection and response systems, emergency venting and dumping.

process control - alarm systems, emergency power supplies, process cooling systems, inertgas systems, safety shutdown systems, computer control, explosion protection

safety programs - management involvement, safety training, maintenance and safetyprocedures


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2) Try to decrease potential size of accidents

Fire protection - structure of fire protection, fire walls, barriers or similar devices

Material isolation/removal - valve systems, ventilation

Fire fighting - fire alarms, water supply, sprinkler, foam, smoke ventilators etc, site

cooperation.

Offsetting Measures


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Summary Mond Index (Initial Assessment)

3. Division of plant into unit 4. Select key material compound or mixture in the unit which gives

the greatest potential for an energy release by combustion,explosion or exothermic reaction. It may be a reactant, a product, anintermediate, the solvent or the catalyst. It is not uncommon for keymaterial to be a mixture. If difficult to select key material, separateassessment should be made for each option and take the mostsevere one.

5. Calculation of material factor for key material, B 5.1 Normal flammable material 5.2 mixtures 5.3 marginally flammable materials 5.4 material of unspecified composition 5.5 reactive combinations of materials 5.6 materials capable of condensed phase explosion


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6. Special material hazards, M 6.1 oxidising materials 6.2 materials giving a combustible gas with water 6.3 mixing and dispersion characteristics, m

6.3.1 low density flammable gases 6.3.2 Liquid flammable gases 6.3.3 cryogenic storage 6.3.4 highly viscous materials 6.3.5 combustible and flammable dusts

6.4 spontaneous heating 6.5 spontaneous polymerisation 6.6 ignition sensitivity 6.7 subject to gaseous explosive decomposition 6.8 capable of gaseous detonation 6.9 condensed phase explosive properties 6.10 other unusual behaviour



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7. General process hazards, P 7.1 handling and physical chages only 7.2 reaction stages

7.2.1 reaction characteristics 7.2.2 batch reactions 7.2.3 multiplicity of reactions carried out in .

7.3 material transfer 7.4 transportable containers



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8. Special process hazards, S 8.1 low pressure 8.2 high pressure, p 8.3 low temperature 8.4 high temperature, t

8.4.1 Flammable materials 8.4.2 material strength

8.5 corrosion and erosion hazards 8.5.1 internal corrosion 8.5.2 external corrosion

8.6 joint and packing leakages 8.7 vibration and load cycling fatigue hazards 8.8 process or reactions difficult to control 8.9 operation in or near flammable range 8.10 greater than average explosion hazard

8.11 dust or mist explosion hazard 8.12 process using high strength gaseous oxidants 8.13 process ignition sensitivity 8.14 electrostatic hazards



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9. Quantity hazards, Q 10. Layout hazards, L

10.1 height, H 10.2 normal working area, N

10.3 structure design 10.3.1 process units 10.3.2 storage units 10.3.3 compressor houses handling flammable gases 10.3.4 materials of high vapour density

10.4 domino effects 10.5 below ground features 10.6 surface drainage 10.7 other features



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11. Acute health hazards, T 11.1 skin effects 11.2 inhalation effects

12. Calculation of indices 12.1 Dow Index, D 12.2 Fire Index, F 12.3 Explosion Indices

12.3.1 Internal Explosion Index, E 12.3.2 Aerial Explosion Index, A

12.4 Overall Hazard rating, R



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Dow Index, D

D=B[1+M/100][1+P/100][1 + {S+Q+L+T}/100] M is special material hazards P is general process hazards

S is special process hazards Q is quantity hazards L layout hazards T is acute health hazards

Go back to Calculation of indices


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Fire Index, F

F=(BxK)/N B is material factor K is offsetting factor (should be set to 1 for

initial assessment) N is normal working area



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Explosion Index, E

Internal Explosion IndexE = 1 + [ (M+P+S)/100]

Aerial Explosion Index A = B(1+m/100)(QHE/1000)(t+273/300)(1+p)



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Overall Hazard Rating, R

R= D[1+(0.2xEx(AF) 1/2 ] D is dow index E is internal explosion index A is aerial explosion index F is fire index


skc5173 week 6b mond index

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