Hazard analysis INDEX

Methods for performing hazard analysis and risk assessment include safety review, checkhsts, Dow Fire and Explosion Index, what-if analysis, hazard and operabihty analysis (HAZOP), failure modes and effects analysis (FMEA), fault tree analysis, and event tree analysis. Other methods are also available, but those given are used most often. 

Chemical Exposure Index (CEI) Chemical Exposure Index, 1994). The CEI provides a method of rating the relative potential of acute health hazard to people from possible chemical release incidents. It may be used for conducting the initial process hazard analysis and it establishes the degree of mrther analysis needed. The CEI also may be used as part of the site review process. 

Note that this index only produces a relative number. Two products with widely different values of the index might be equally safe if, in fact, neither impedes escape. Conversely, two products with apparently similar values may produce different hazard levels if both products are close to the margin of safety. Thus, the scale for any index must be "calibrated", and it may well be different for each building or type of occupant. Generally, this will require a more complete hazard analysis and/or full-scale fire tests. Protocols for doing this are currently under consideration. 

Chemical Exposure Index (CEI) (Chemical Exposure Index, 1994 Mannan, 2005, pp. 8/22-8/26.) The CEI provides a method of rating the relative potential of acute health hazard to people from possible chemical release incidents. It may be used for prioritizing initial process hazard analysis and establishing the degree of further analysis needed. The CEI also may be used as part of the site review process. The system provides a method of ranking one risk relative to another. It is not intended to define a particular containment system as safe or unsafe, but provides a way of comparing toxic hazards. It deals with acute, not chronic, releases. Flammability and explosion hazards are not included in this index. To develop a CEI, information needs include... 

Software System Hazard Analysis This type of analysis is conducted similar to a hardware system hazard analysis (SHA), analyzing software functional processing steps to determine whether they may have any particular hazardous effect on the system. The analysis utilizes a hazard-risk index to illustrate the severity of each potential failure. The main advantage to this method is in its ability to positively identify safety-critical hardware and software functions as well as consider the effect of the human element in system software operations. The results of the software SHA, which identifies single-point failures or errors within a system, can often be used to assist in the development of a software fault tree analysis or, to some degree, a system FMEA. However, as with the other various SWHA techniques briefly described above, this method is also time-consuming and costly to perform. 

The risk indexes of debris flow are evaluated by geological hazard analysis assessment method. The risk indexes of Zhiyang valley are analyzed and the risk analysis structure model of debris flow is established. 

Several risk indices have been practiced by the chemical and manufacturing industries over the past 50 years (see Table 8.5) (Heikkila, 1999). The important ones among these indices are the Dow Fire and Explosion Index, the Dow Chemical Exposure Index, the HAZAN (Hazard Analysis), and the Prototype Index of Inherent Safety. 

Several methods are available for identifying and assessing hazards (Kletz, 1990). Hazards can be identified through checklists, failure mode effect analysis (FMEA), fault tree analysis, event tree analysis, what-if analysis, and hazard and operability studies (HAZOP). Assessing hazards can be done through hazard analysis (HAZAN), codes of practice, the Dow Explosion Index, and prototype index of inherent safety (PIIS). 

It is prudent that a few terms associated with PHA, mainly for PSM systems, are discussed. In Table II/2.1.2-1, a few hazard analysis methods have been highlighted such as the Dow FEI and the Mond Index, etc. for quick risk assessment in process plants. 

Process Hazard Analysis Dow Fire and Explosion Index, ChE 258 Chemical Process Safety University of Missouri — Rolla. 

Chapters 5 through 9 are the best sources for tools to identity risk in the system. Once the system is defined, developing a quick preliminary hazard list will detect the gross hazards of concern to the system. The hazard analysis further refines the hazard list and clearly recognizes which hazards are of greatest concern. Also, the Hazard Risk Index is a good qualitative tool with which to note some of the qualitative risks that are required in step 6 of the risk assessment methodology. 

The Dow Fire Explosion Index was developed by Dow Chemical in the 1960s and is today used by many companies to identify high-risk systems. It is a form of process hazards analysis that focuses on fires or explosions, but it also goes beyond the identification of these hazards to quantifying the probable loss from a resulting fire or explosion. 

U.S. Department of Labor, Occupational Safety and Health Administration. Job Hazard Analysis and Control (I9I0.9I7-922), Subject Index. Internet 2001. Available at http //www.osha.gov. 

The DAL is an index number ranking the safety-criticality of the system functions. This ranking implies that in order to make the system safe, greater development rigor must be applied to each successively critical level. Table 2.3 correlates the hardware DALs to the five classes of failure conditions and provides definitions of hardware failure conditions and their respective DALs. Initially, the hardware DAL for each hardware function is determined by the SSA process using a functional hazard analysis (FHA) to identify potential hazards and then the preliminary system safety assessment (PSSA) process allocates the safety requirements and associated failure conditions to the function implemented in the hardware. 

See Hazard Risk Index (HRI) Matrix for additional related information. MISHAP RISK ANALYSIS... 

The first step in the procedure is to conceptually divide the process into separate process units. A process unit is a single pump, a reactor, or a storage tank. A large process results in hundreds of individual units. It is not practical to apply the fire and explosion index to all these units. The usual approach is to select only the units that experience shows to have the highest likelihood of a hazard. A process safety checklist or hazards survey is frequently used to select the most hazardous units for further analysis. 

Figure 10-4 Form used for consequences analysis. Source Dow s Fire and Explosion Index Hazard Classification Guide, 7th ed., 1994. Reproduced by permission of the American Institute of Chemical Engineers.

Computing the index of Hazard on the base of chemical analysis and attribution to the class of hazard... 

For the purposes of this example, it was assumed that the waste was placed 4 m deep and covered with a cap and soil that was at least 3 m thick. As a consequence, the assumed scenario was an onsite drilling event. The dose analysis assumes a two-fold volume increase (50 percent dilution) of the drill tailings by uncontaminated material. The mixture of waste and uncontaminated cover material is spread on the surface of the site, and individuals working in the area are exposed to the tailings for 1,000 h. The thickness of the layer of contaminated drill tailings is assumed to be about 5 cm and the area to be about 3.3 m2. Using dose as a surrogate for risk, analysis of this scenario yields a dose of0.002 mSv from all radionuclides. Since the assumed allowable dose is 20 mSv (see Table 7.1), the risk index would be 0.002/20 = 10 4, which is well below the value of unity, and the waste would be classified as low-hazard. 

Given the assumption that an acceptable stochastic risk from disposal in a hazardous waste facility is about 10 3 (see Table 7.1), the stochastic risk index due to the presence of radionuclides in the electric arc furnace waste is (2.5 X 10 5)/10 3 = 0.025. Since this result is much less than unity, the waste clearly would be classified as low-hazard due only to the presence of 137Cs, and there is no need to perform a less conservative analysis. 

---