Hazard severity 512 INDEX

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. 

Equally important to assessing the probability and severity of the hazardous event is knowing what to do with that information. The hazard risk index (HRI), coupled with the risk decision criteria, indicates how the hazard should be treated. Obviously, if the hazard is catastrophic aud frequent, it must be coutrolled immediately. So, an HRI of IE, 2E, 3D, 3E, 4A, or 4B would have a lower priority for corrective action than one of lA, IB, 1C, 2A, 2B, or 3A. 

Of course, the problem is the danger of quantifying information that is not easily quantifiable. When data are too ambiguous or nebulous to be of utility, you can use a pseudo-quantification approach such as the hazard risk index. Risk assessment is based on the numerical comparison between risk events. Part of the risk assessment process is to compare, contrast, and evaluate risks. This risk evaluation becomes a ranking and comparison process and uses probability differences (matched with other factors such as severity of consequences) to do it. 

The HRI is an index number indicating qualitatively the relative risk of a hazard. It is derived from the HRI matrix by identifying the matrix cell resulting from the intersection of the hazard likelihood and hazard severity values. In a typical HRI matrix, such as the matrix in MIL-STD-882, there are 20 cells created by a 4 x 5 matrix. The matrix cells are labeled with an index number of 1 through 20, where 1 represents the highest risk and 20 the lowest risk. The smaller the HRI number, the higher the safety risk presented by the hazard. The HRI number establishes the safety significance of a hazard and who can accept the risk for the hazard. It should be noted that the HRI is also often referred to as the mishap risk index (MRI). However, since hazard risk and mishap risk are really the same entity, then the HRI and the MRI are really the same entity, just viewed from two different perspectives. 

The Hazard Risk Index (HRI) matrix is a risk management tool used by system safety for hazard/mishap risk assessment. The HRI matrix establishes the relative level of potential mishap risk presented by an individual hazard. By comparing the calculated qualitative severity and likelihood values for a hazard against the predefined criteria in the HRI matrix, a level of risk is... 

The relative risk index (or HRI) is derived from the matrix cell resulting from the intersection of the likelihood and severity axes that represent a particular hazard. The HRI matrix maps hazard severity on one axis and hazard likelihood on the other axis. Once a hazard s severity and likelihood are determined, they are mapped to a particular HRI matrix cell, which yields the hazard index and the relative risk for that hazard. The hazard risk level establishes who can accept the risk by authority level. 

An RPN is the risk ranking index for reliability, where RPN = (probability of occurrence) x (severity ranking) x (detection ranking). This number typically appears on the reliability oriented FMECA. It should be noted that the RPN is not the same as a Hazard Risk Index which is derived from probability of occurrence and severity of a hazard. The RPN provides a risk ranking order of components for reliability improvement. 

The UK MOD base their acceptance of hazards on a risk classification scheme, which is based on the combination of the severity, probability and time of exposure for each particular hazard. For the purposes of the accident risk classification scheme, accidents are considered single events (Table B.9). These classifications can be combined to determine a hazard risk index (HRI), which is a numerical risk factor that can be used to prioritise the need for corrective action or resolution. The HRI matrix in Table B. 10 is an example showing how the hazard severity and the hazard probability categories combine to yield the HRI. 

To assess tlie overall potential for noncarcinogenic effects posed by more dian one chemical, a liazard index (HI) approach has been developed based on EPA s Guidelines for Healdi Risk Assessment of Chemical Mixtures. This approach assumes that simultaneous subtlu eshold exposures to several chemicals could result in an adverse healtli effect. It also assumes tliat tlie magnitude of the adverse effect will be proportional to tlie sum of the ratios of the subtlireshold exposures to acceptable exposures. The non cancer hazard index is equal to tlie sum of the hazard quotients, as described below, where E and tlie RfD represent the same exposure period (e.g., subclironic, clironic, or shorter-term). 

The approach to developing metrics for process safety is analogous to those that might be used to assess Occupational Exposure risk. One can cite as well several indices that have been developed as metrics for estimating and ranking the safety of a given process or chemical reaction, such as the DOW fire and explosion index,the Stoessel index ° for hazard assessment and classification of chemical reactions, the Inherent Safety Index, the Prototype Index for Inherent Safety, amongst others. ... 

Most of the isolated diacyl (including sulfonyl) peroxides are solids with relatively low decomposition temperatures, and are explosive, sensitive to shock, heat or friction. Several, particularly the lower members, will detonate on the slightest disturbance. Autocatalytic (self-accelerating) decomposition, which is promoted by tertiary amines, is involved [1]. Solvents suitable for preparation of safe solutions of diacetyl, dipropionyl, diisobutyryl and di-2-phenylpropionyl peroxides are disclosed [2], The class is reviewed, including hazards and safety measures [3], Cyclic diacyl peroxides are more stable, but scarcely to be trusted. Individually indexed compounds are ... 

Several benzyl derivatives exhibit potentially hazardous properties arising from the activation by the adjacent phenyl group, either of the substituent or of a hydrogen atom. Halides, in particular, are prone to autocatalytic Friedel Crafts polymerisation if the aromatic nucleus is not deactivated by electron withdrawing substituents. Individually indexed compounds are ... 

As seen further on in this chapter, individual PEEP index values express a condensed portrait of an effluent s hazard potential which takes into account several important ecotoxicological notions (toxic intensity and scope in terms of biotic levels impacted, bioavailability, persistence of toxicity and effluent flow). Unlike wastewater investigations limited to chemical characterization, this bioassay-based scale reflects the integrated responses of several representative toxicity tests to all interaction phenomena (antagonistic, additive and/or synergistic effects) that can be present in effluent samples. 

The same procedure above may be applied for simultaneous shorler-lenn exposures to several chemicals. For drinking water exposures, 1- and 10-day Hcallli Advisories can be used as reference toxicity values. Depending on available data, a separate hazard index might also be calculated for developmental toxicants (using RfDj,s), wliich might cause adverse effects following exposures of only a few days. 

A precursor to a toxicity index is the common use of tests to rank environmental samples or hazardous sites according to the severity of the toxic responses. Toxicity ranking defines priority for action on the most toxic effluents or contaminated sites. Ranking the samples can become complicated if toxicity has been measured with several tests that produced variations in rank. Joining the responses into a toxicity index would express potential hazard in a single number. 

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