Mond index

Process industry has used the Dow Fire and Explosion Hazard Index (DOW, 1987) and the Mond Index (ICI, 1985) for many years. These indices deal with fire and explosion hazard rating of process plants. Dow and Mond Indices are rapid hazard-assessment methods for use on chemical plant, during process and plant development, and in the design of plant layout. They are best suited to later design stages when process equipment, chemical substances and process conditions are known. 

Another widely used safety analysis method in process industry is the Hazard and Operability Analysis, better known as Hazop (Kletz, 1992). The conventional Hazop is developed to identify probable process disturbances when complete process and instrumentation diagrams are available. Therefore it is not very applicable to conceptual process design. Kletz has also mentioned a Hazop of a flowsheet, which can be used in preliminary process design, but it is not widely used. More usable method in preliminary process design is PIIS (Edwards and Lawrence, 1993), which has been developed to select safe process routes. 

Other possible preliminary safety analysis methods are concept safety review (CSR), critical examination of system safety (CE), concept hazard analysis (CHA), preliminary consequence analysis (PCA) and preliminary hazard analysis (PHA) (Wells et al., 1993). These methods are meant to be carried out from the time of the concept safety review until such time as reasonably firm process flow diagrams or early P I diagrams are available. 

CSR provides the means for an early assessment of safety, health and 

The Dow Fire and Explosion Hazard Index, the Mond Index, Hazop and PIIS are discussed here in more detail. The methods and their elements are also presented in Table 1. 

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Tools are available to assist in comparing the risk associated with two or more different processes. For example, the first sheet of the Dow Fire and Explosion Index (FEI) (Dow, 1994b) ranks the safety characteristics of the process from a fire/explosion standpoint, without taking credit for protective and mitigation features. The Dow Chemical Exposure Index (CEI) (Dow, 1994a) and Id s Mond Index (ICI, 1985 Tyler, 1985) are other ranking tools. 

Imperial Chemical Industries (ICI) (1985). The Mond Index, Second Edition. Win-nington, Northwich, Chesire, U. K. Imperial Chemical Industries PLC. 

Tyler, B. J. (1985). Using the Mond Index to Measure Inherent Hazards." Plant/Op-erations Progress 4, 3 (July), 172-75. 

Imperial Chemical Industries PLC, Explosion Hazards Section, Technical Department. The Mond Index How to Identify, assess and minimize potential hazards on chemical plant units for new and existing processes. Second Edition. Winnington, Northwich Cheshire. 

Other techniques that take into account some site-specific conditions, such as the Dow Fire and Explosion Index (Ref. 34) and the Mond Index (Ref. 39), have been used to prioritize buildings for evaluation. The results of these indices should be used in conjunction with consideration of other factors, rather than as stand-alone criteria. These other factors might include an evaluation of the effects of confinement and/or congestion-induced turbulence on the potential for blast. 

The process is first divided into a number of units which are assessed individually. The dominant material for each unit is then selected and its material factor determined. The material factor in the Mond index is a function of the energy content per unit weight (the heat of combustion). 

The Dow and Mond indexes are useful techniques, which can be used in the early stages of a project design to evaluate the hazards and risks of the proposed process. 

ICI (1993) Mond Index How to Identify, Assess and Minimise Potential Hazards on Chemical Plant Units for New and Existing Processes. 2nd edn, ICI, Northwich. 

The Dow and Mond Indexes provide a relative ranking of the hazards and risks in a chemical process plant. This is accomplished by assigning penalties and credits based on plant features such as the presence of hazardous materials and the safety devices which can mitigate any hazardous effects. Penalties and credits are then combined into a single hazard index for the process unit in question. 

The Mond Index (ICI, 1985) has been developed from the 1973 version of the Dow F E Index. The principal modifications to the Dow method include (Lees, 1996) 1) wider range of processes and storage installations can be studied, 2) covers processing of chemicals having explosive properties, 3) improved hazard consideration for hydrogen, 4) additional special process hazards, 5) toxicity included into the assesment. 

In the Mond Index the plant is divided into individual units on the basis of the feasibility of creating separating barriers. One of the factors taken into account in the index is therefore plant layout. The potential hazard is expressed in terms of the initial value of a set of indices for fire, explosion and toxicity. A hazard factor review is then carried out to see if design changes reduce the hazard, and intermediate values of the indices are determined. Offsetting factors for preventative and protective features are applied and the final values of the indices, or offset indices, are calculated. The elements of the Mond method are listed in Table 1. 

Mond Index Material factor Special material hazards General process hazards Special process hazards Quantity factor Layout hazards Toxicity hazards... 

Predesign (Conceptual design) flow sheet preliminary pid feasibility study preliminary operation instructions material balance energy balance process concept operating conditions sketch of layout isi, pns (coarse Dow F E Index, Mond Index, Hazop)... 

Basic engineering final flow sheets final PID data sheets for equipment, piping, process data on equipment, piping and instruments operating, start-up and shut-down procedures Dow F E Index, Mond Index, Hazop, Hazan, Fault tree, RISKAT... 

Detailed engineering equipment specifications piping specifications instrument specifications electrical specifications control specifications construction specifications detailed engineering data for equipment, piping, instruments, controls, electrical, constructions etc. layout Hazop, Dow F E Index, Mond Index, Fault tree... 

Operation operation reports operation data operation experience Hazop, Dow F E Index, Mond Index, Fault tree... 

Also indices such as the Dow Fire and Explosion Hazard Index and the Mond Index have been suggested to measure the degree of inherent SHE of a process. Rushton et al. (1994) pointed out that these indices can be used for the assessment of existing plants or at the detailed design stages. They require detailed plant specifications such as the plot plan, equipment sizes, material inventories and flows. Checklists, interaction matrices, Hazop and other hazard identification tools are also usable for the evaluation, because all hazards must be identified and their potential consequences must be understood. E.g. Hazop can be used in different stages of process design but in restricted mode. A complete Hazop-study requires final process plans with flow sheets and PIDs. 

Health hazards caused by chemicals are represented by the Toxic Exposure Subindex (ITox). hi the ISI the evaluation of toxic exposure is based on the Threshold Limit Values (TLV) because TLV data is readily available for most substances in process industry. TLV values express the harmful exposure limits of substances in the threshold time of 8 hours. The index value is higher, when the TLV is lower i.e. the substance is more toxic. It is important to use TLVs with same threshold time so that the results are comparable. Score limits in Table 13 are based on Mond Index (ICI, 1985). 

For OSBL inventory values based on Mond Index (ICI, 1985) were used. These were used also for ISBL by Edwards et al. (1993) but the experts criticized this, since the relevant inventory scale in ISBL is much smaller (Lawrence, 1996). Also due to a tighter layout the same inventory in ISBL is more dangerous than in OSBL. Therefore a new scale was developed by scaling the Mond values by using the expert recommendations in Lawrence s work (1996). See Table 15. 

ICI Mond Division. 1985. The Mond Index. 2nd ed. Imperial Chemical Industries pic, Explosion Hazards Section, Technical Department, Winnington, Nortwich, Cheshire CW8 4DJ. 

The Dow index applies only to main process units and does not cover process auxiliaries. Also, only fire and explosion hazards are considered. Recently the index has been expanded to include business-interruption losses. The principles and general approach used in the Dow method of hazard evaluation have been further developed by Mond in the United Kingdom to include toxicity hazards. This revised Mond index is described in a paper by Lewis ... 

The Mond index was developed from the Dow F El by personnel at the ICI Mond division. The third edition of the Dow index, Dow (1973), was extended to cover a wider range of process and storage installations, the processing of chemicals with explosive properties, and the evaluation of a toxicity hazards index. Also included was... 

The ICI-MOND Fire Explosion and Toxicity Index (ICI 1985) was derived from DOW one and it is yet appreciated in process industry in many countries, including Italy. In ICI-MOND index method there are some ninety elementary questions, nested in a three levels tree. For many issues there is also a forth level of nested questions. About two thirds of the questions are for penalties and one third for credits accounting. For the most of the questions a quantitative answer is required. The questions are organized in chapters for penalties section the subjects are related to materials and quantities, processes and equipment, layout, health for credits section instead the method deals with containment, control, safety culture, fire engineering and emergency preparedness. Every issue weighs differently in overall risk levels accounting. Results are presented in a structured way, discriminat-iug fire, toxic, confined and unconfined explosion. 

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