Quantitative analysis method for safety assessment of hazardous chemicals

DOW chemistry and IC Mond method should not be considered as one of the quantitative analysis tools. If these tools are also called quantitative tools, it may be misleading.

The Fire and Explosion Hazard Index Evaluation Method (Seventh Edition) of the American Dow Chemical Company is an objective evaluation method that uses a step-by-step calculation method to calculate the potential fire, explosion and reactivity risks of process equipment and materials contained therein. The quantitative basis in the evaluation process is the statistical data of past accidents, the potential energy of materials and the status of current safety and disaster prevention measures. This method calculates the fire and explosion hazard index, proposes the risk of the operation process, and considers the measures that should be taken. ； Then, the purpose of prevention and control is achieved by calculating the compensation fire and explosion risk index. The purpose of the evaluation of this law is to: Objectively quantify expected losses from potential fire, explosion and reactive incidents ； Identify equipment that may cause or amplify an accident ； Notify management of potential fire and explosion hazards ； Let engineers understand the possible losses caused by process parts and help them determine effective and economical ways to reduce the severity of potential accidents and total losses. Fire and explosion hazard index evaluation generally goes through the following steps:: 1. Determine the evaluation unit ； 2. Find the material coefficient in the unit ； 3. According to the process conditions of the unit, select appropriate hazard coefficients and record them in the "General process hazard coefficient F1" and "Special process hazard coefficient F2" columns of the fire and explosion hazard index table. ； 4. Multiply the general process hazard coefficient F1 and the special process hazard coefficient F2 to obtain the process unit hazard coefficient F3. ； 5. Multiply the process unit hazard coefficient F3 and the material coefficient to calculate the fire and explosion hazard index (F&EⅠ). Determine the hazard level of the unit based on the fire and explosion hazard index and hazard level table, and complete the initial evaluation of the unit hazard degree. ； 6. According to the safety facilities equipped in the unit, select various coefficients and calculate the safety compensation coefficient ； 7. Use the safety compensation coefficient to calculate the compensation fire and explosion hazard index (F&EⅠ)′ ； 8. Determine the hazard level of the unit after compensation according to the compensated fire and explosion hazard index (F&EⅠ)′, and calculate the radius and area of ​​the exposed area of ​​the unit.

Evaluation process of fire and explosion risk index evaluation method 1. Process unit selection Process unit refers to any main unit of the process device, and the warehouse can also be used as a process unit. Most factories are composed of multiple units, but when calculating the fire and explosion index, only those process units that have an impact on the process from the perspective of loss prevention are selected for evaluation. These units are called appropriate process units, or process units for short. 2. Initial evaluation of unit risk The result of the initial evaluation is the evaluation of the inherent risk of the unit, which represents the inherent risk of the unit without considering any preventive measures. Fire and explosion hazard index (F&EⅠ) is calculated according to the following formula: F&EⅠ=F3 •MF where: F3—Process unit hazard coefficient, F3=F1·F2 MF—Material coefficient F1—General process hazard coefficient F2—Special process hazard coefficient. After calculating F&EⅠ, determine its degree of hazard according to the fire and explosion hazard index and hazard level table (Appendix Table 4-3-5), which allows people to have a relative understanding of the severity of fire and explosion. Table 4-3-5 F&EⅠ and hazard level table F&EⅠ 1～60 61～96 97～127 128～158 >159 Hazard level I Ⅱ Ⅲ Ⅳ V The risk is lightest, light, medium, very large, very large 3. Final evaluation of unit risk (1) How to obtain the safety compensation coefficient. Starting from reducing the actual risk of the unit, chemical companies can reduce the risk of the unit by changing the design, reducing the frequency of accidents and potential accident scale, safety countermeasures and various preventive measures. Safety precautions are divided into three aspects: process control, material isolation, and fire prevention measures. Among them, the process control compensation coefficient includes 9 measures such as emergency power supply. ； The material isolation compensation coefficient includes 4 measures including remote control valves ； The compensation coefficient for fire prevention measures includes 9 measures including leakage detection devices. The values ​​of the compensation coefficients are selected according to the values ​​recommended by "DOW Chemistry 7th Edition" ； When no safety measures are taken, the above compensation coefficient is 1.0. (2) The final evaluation of unit risk uses the calculated safety compensation coefficient to obtain the compensated fire and explosion risk index. Compensation fire and explosion hazard index (F&EⅠ)′ is calculated according to the following formula: (F&EⅠ)′=F&EⅠ·C where: C—Total compensation coefficient of safety measures, C=C1·C2·C3 ； C1—Process control compensation coefficient C2—Material isolation compensation coefficient C3—Fire prevention measures compensation coefficient (3) Calculate the radius of the exposed area The radius of the exposed area is calculated according to the following formula: Radius of exposed area R=0.84×0.3048×(F&EⅠ)′

Quantitative analysis can be considered from two aspects: Simulation of the possibility of accidents and their consequences. Fault tree analysis and event tree analysis can be used to evaluate the likelihood of accidents. ； Vapor cloud explosion model is used to simulate accident consequences. Risk analysis considers both the likelihood and consequences of an accident. Methods of this type include: Risk matrix method, layer of protection analysis (LOPA), etc.

No matter how to evaluate or what method is used, it is all based on illusions and empirical values. The ultimate goal of the evaluation should be to give a maximum accident damage range, so as to facilitate the enterprise to formulate emergency plans and determine the layout. Real quantitative data can only be obtained from the laboratory or by extrapolation after an accident.