Hazard Assessment Procedures

Thermal runaway is a partieular problem in unsteady state bateh reaetions, where the rate of reaetion and, therefore, the rate of heat produetion varies with time. The eonsequenees of thermal runaway are sometimes severe as in the ineidents at Seveso [3]. In this ease, a bursting disk ruptured on a reaetor. The reaetor was used to manu-faeture triehlorophenol at a temperature of 170-185°C and was heated 

These faetors are attributed to bateh and semi-bateh proeesses rather than eontinuous proeesses. However, the use of eontinuous proeesses on fine ehemieal manufaeturing sites is limited. It is often preferable to use the semi-bateh mode as opposed to bateh proeesses. The Appendix lists hazards of pertinent ehemieal reaetions for toxie and reaetive hazards ehemieals. Information eoneerning the safety of various ehemieals (e.g., ammonia and others) ean be readily obtained from the World Wide Web. Table 12-1 shows how to aeeess a material safety data sheet at the Vermont Safety Information (VIRI) site on the Internet. 

Temperature-indueed runaways have many eauses ineluding loss of eooling, loss of agitation, and exeessive heating. During a temperature- 

Accessing a material safety data sheet (MSDS) 

When the first screen appears, click on SIRI MSDS collection-Vermont site. 

The task of specifying the design, operation, and control of a reactor with stirrer, heating, or cooling coils, reflux facilities, and emergency relief venting can pose a problem if all the time-dependent parameters are not considered. The use of batch processing techniques in the fine chemical industry is often characterized by  

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Further information and examples of inherently safer design methods are given in references 3, 5 and 6. It should be noted that the successful incorporation of such measures normally depends oh the hazard assessment procedure starting at an early stage in the process development. 

Recently, a formalized hazard assessment procedure has been initiated for all processes to be run in the Pilot Plant. To date, the testing methodology has been found to be quite effective at identifying potential hazards. For the remainder of this paper, I will elaborate on this procedure, detail its step-by-step format as well as the responsibilities of the individuals involved. 

Fig. 1. Flow chart representing the complete hazard identification and risk assessment procedure.

The hazard analysis and risk assessment procedure can be appHed at any stage in the lifetime of a process or procedure including research and... 

There are a large number of standard methods suitable for each stage in the hazard analysis and risk assessment procedure. The selection of the proper method depends on several factors. Some of these are the type of process, the stage in the lifetime of the process, the experience and capabiUties of the participants, and the step in the procedure that is being examined. Information regarding the selection of the proper procedure is available in an excellent and comprehensive reference (1). 

The remaining step in the hazard identification and risk assessment procedure shown in Figure 1 is to decide on risk acceptance. For this step, few resources are available and analysts are left basically by themselves. Some companies have formal risk acceptance criteria. Most companies, however, use the results on a relative basis. That is, the results are compared to another process or processes where hazards and risks are weU-characterized. 

Process Safety Analysis This part treats the analysis of a process or project from the standpoint of hazards, risks, procedures for making potential damage estimates, and project reviews and audits. It can be helpful to management in assessing risks in a project. It consists of the following ... 

Are there procedures for performing PPE hazard assessments, specifying PPE and training employees on required PPE ... 

Risk analysis A methodical examination of a process plant and procedure that identifies hazards, assesses risks, and proposes measures that will reduce risks to an acceptable level. 

The two approaches lead to completely different procedures for vapor cloud explosion hazard assessment. If conventional TNT-equivalency methods are applied, explosive potential is primarily determined by the amount of fuel present in a cloud, whether or not within flammability limits. The cloud center is the potential blast center and is determined by cloud drift. 

The Woodlawn Plant has completed installation of its Management of Change procedure, and the Kingston Plant is continuing to implement process hazard assessment. The assignment of a new plant manager to the Winston Plant has delayed their installation efforts by one month. 

CPI. The first book, Guidelines for Hazard Evaluation Procedures (HEP Guidelines), eovers methods for identifying and qualitatively assessing chemical process hazards. 

FIGURE 7.1.3 Process of hazard identification, Source SSC, First report on the harmonisation of risk assessment procedures, Part 1, October 2000. )... 

Risk characterization is the last step in the risk assessment procedure. It is the quantitative or semi-quantitative estimation, including uncertainties, of frequency and severity of known or potential adverse health effects in a given population based on the previous steps. Risk characterization is the step that integrates information on hazard and exposure to estimate the magnitude of a risk. Comparison of the numerical output of hazard characterization with the estimated intake will give an indication of whether the estimated intake is a health concern. ... 

The degree of confidence in the final estimation of risk depends on variability, uncertainty, and assumptions identified in all previous steps. The nature of the information available for risk characterization and the associated uncertainties can vary widely, and no single approach is suitable for all hazard and exposure scenarios. In cases in which risk characterization is concluded before human exposure occurs, for example, with food additives that require prior approval, both hazard identification and hazard characterization are largely dependent on animal experiments. And exposure is a theoretical estimate based on predicted uses or residue levels. In contrast, in cases of prior human exposure, hazard identification and hazard characterization may be based on studies in humans and exposure assessment can be based on real-life, actual intake measurements. The influence of estimates and assumptions can be evaluated by using sensitivity and uncertainty analyses. - Risk assessment procedures differ in a range of possible options from relatively unso-... 

This chapter provides general information for performing qualitative or quantitative risk assessments on buildings in process plants. For detailed guidance on risk assessment techniques, the user is referred to other CCPS books on this subject, including Reference 3, Guidelines for Hazard Evaluation Procedures, Second Edition, and Reference 4, Guidelines for Chemical Process Quantitative Risk Analysis. 

The terminology used varies considerably. Hazard identification and risk assessment are sometimes combined into a general category called hazard evaluation. Risk assessment is sometimes called hazard analysis. A risk assessment procedure that determines probabilities is frequently called probabilistic risk assessment (PRA), whereas a procedure that determines probability and consequences is called quantitative risk analysis (QRA). 

Figure 10-1 Hazards identification and risk assessment procedure. Adapted from Guidelines for Hazards Evaluation Procedures (New York American Institute of Chemical Engineers, 1985), pp. 1-9.

The hazards identification procedures presented in chapter 10 include some aspects of risk assessment. The Dow F EI includes a calculation of the maximum probable property damage (MPPD) and the maximum probable days outage (MPDO). This is a form of consequences analysis. However, these numbers are obtained by some rather simple calculations involving published correlations. Hazard and operability (HAZOP) studies provide information on how a particular accident occurs. This is a form of incident identification. No probabilities or numbers are used with the typical HAZOP study, although the experience of the review committee is used to decide on an appropriate course of action. 

A special assessment procedure that aims at tackling uncertain consequences of human activities is called risk assessment (RA). The main objective of risk assessment is to use the best available information and knowledge for identifying hazards, estimating the risks and making recommendations for risk management (World Bank, 1997). 

When applied to a particular site and/or project, RA procedures include several generic steps such as hazard identification, hazard assessment, risk estimation and risk evaluation. 

Figure 23-1 shows the hazards identification and risk assessment procedure. The procedure begins with a complete description of the process. This includes detailed PFD and P I diagrams, complete specifications on all equipment, maintenance records, operating procedures, and so forth. A hazard identification procedure is then selected (see Haz-ard Analysis subsection) to identify the hazards and their nature. This is followed by identification of all potential event sequences and potential incidents (scenarios) that can result in loss of control of energy or material. Next is an evaluation of both the consequences and the probability. The consequences are estimated by using source models (to describe the... 

General References Guidelines for Hazard Evaluation Procedures, Second Edition with Worked Examples, American Institute of Chemical Engineers, New York, 1992 Layer of Protection Analysis A Simplified Risk Assessment Approach, American Institute of Chemical Engineers, New York, 2001 ISA TR84.00.02, Safety Instrumented Functions (SIF)—Safety Integrity Level (SIL) Evaluation Techniques, Instrumentation, Systems, and Automation Society, N.C., 2002. 

The clean-out operation, which had not been done in the previous 30 years, was not subjected to a hazard assessment to devise a safe system of work, and there were defects in the planning of and permit-to-work system of the operation. The task was largely handled locally with minimal reference to senior management and with lack of formal procedures, although such procedures existed for cleaning other still bases on the site. The permits were issued by a team leader who had not worked on the Meissner plant for 10 years prior to his appointment on September 7. At 10 15 a.m., he made out a permit for a fitter to remove the manlid. The fitter signed on about 11 10 a.m. and shortly after went to lunch. Operatives who were standing by offered to remove the manlid and the same team leader made out a permit for them to do so. When the fitter returned from lunch, it was realized that the still base inlet had not been isolated and a further permit was issued for this to be done. 

Many of the earliest methods available for the measurement of carbohydrates were based on their chemical reactivity and involved the addition of a particular reagent with the subsequent formation of a coloured product. Although the cheapness and technical simplicity of these procedures contributed to their previous popularity, they are inherently non-specific and often involve the use of substances that are now recognized as hazardous. It is essential that the hazard assessment is undertaken before using such techniques. 

ECETOC (2004) has proposed a concept of generic threshold values based on hazard categories primarily intended to be used in the risk assessment procedure of industrial chemicals within REACH. The hazard categories are based on EU classihcation limits and for each substance to be risk assessed, inclusion in hazard categories depends on the substance s specific classification (or no classification) according to the Commission Directive 67/548/EC (EC 1967). Three hazard categories have been suggested ... 

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