Hazard probability

The hazard probability levels listed in Table 2.2 (MIL-STD-882) represent a quah-tative judgment on the relahve likelihood of occurrence of a mishap caused by the uncorrected or uncontrolled hazard. Here again, based upon a high probability that a situation will occur, a judgment can be made as to the importance of addressing one specific concern over another. 

Therefore, when using the severity and probability techniques simultaneously, hazards can be examined, qualified, addressed, and resolved based upon the hazardous severity of a potential outcome and the likelihood that such an outcome will occur. For example, while an aircraft collision in midair would unarguably be classified as a Category I mishap (catastrophic), the hazard probability would fall into the Level D (remote) classification based upon statistical history of midair collision occurrence. The system safety effort in this case would require specific, but relatively minimal 

Critical 11 Severe injury, occupational illness, or system damage 

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Ref. 39 suggests an initial qualitative hazards analysis early in systems design, with only general levels of hazard probabilities identified, in addition to severity categories. An example of such a qualitative ranking from Ref. 39 appears in Table V. 

Table V. Example of Qualitative Hazard Probability Ranking (Ref. 39)...

Likelihood of Hazard. The NEC recognizes two distinct levels of hazard probability. Division 1 denotes an environment in which the probability exists that sufficient levels of the hazardous element may always exist, under normal operating condition, as to warrant extreme protections. Whereas, Division 2 denotes an environment where the probability for sufficient levels of the hazardous element to exist, under normal operating conditions, is less likely, and therefore, the extreme protection is not justifiable. Further areas adjacent to Division 1 areas can often constitute classification as Division 2 environments. 

Hazard Probability - Hazard Severity i VERY UNLIKELY UNLIKELY RATHER UNLIKELY... 

Identified Hazard Hazard Probability Hazard Severity Estimated Risk Acceptability... 

Use of a combination of the hazard severity and hazard probability tables given allow a quahtative assessment of risk from which determinations can be made that risks are acceptable, or not acceptable, and from which priorities can be set for actions to be taken. 

Hazard probability is defined as the aggregate of the likelihood that the potentials of hazards will be realized and that a hazards-related incident will occur. Hazard probability is to be described in probable occurrences per unit of time, events, population, items, or activity. 

The FTA can be used to determine the following minimal cut sets that cause a hazard, probabilities of the hazard and faults. However, when designing such real-time systems like logistic support of operational system performance, the following time parameters delay time between the causes and effect, hazard tolerance time, fault detection time, administrative delay time often have to be analyzed. In standard FTA, the above time parameters are not considered, but can be expressed in Fault Trees with Time Dependencies (FTTD). 

Major Hazards Probable human carcinogen (OSHA "select carcinogen") moderate acnte toxicity highly flanunable. 

Risk An expression of the possibility of a mishap in terms of hazard severity and hazard probability. 

Hazard probability The aggregate probability of occurrence of the individual hazardous events that create a specific hazard (MIL-STD-882). 

Risk Mathematically, expected loss the probability of an accident multiplied by the quantified consequence of the accident (SSDC) an expression of the possibility of a mishap in terms of hazard severity and hazard probability (MIL-STD-882) note Hazard exposure is sometimes included (AFR 800-16) as defined in NHB 5300.4(10-2), The chance (qualitative) of loss of personnel capability, loss of system, or damage to or loss of equipment or property (NSTS 22254) a measure of both the probability and the consequence of all hazards of an activity or condition. A subjective evaluation of relative failure potential. In insurance, a person or thing insured (ASSE). 

Table 2.3 shows the hazard risk matrix, which incorporates the elements of the hazard severity table and the hazard probability table to provide an effective tool for approximating acceptable and unacceptable levels or degrees of risk. By establishing an alphanumeric weighting system for risk occurrence in each severity category and level of probability, one can further classify and assess risk by degree of acceptance. Obviously, from a systems standpoint, use of such a matrix facilitates the risk assessment process. 

Design for Minimum Risk The system safety order of precedence dictates that, from the first stages of product or system design, the system should be designed for the elimination of hazards, if possible. Unfortunately, in the real world, this is not always practical or feasible. If an identified hazard cannot be eliminated, then the risk associated with it should be reduced to an acceptable level of hazard probability through design selection. 

Example AN/PAQ-4C, Infrared aiming light (830 nm) below 0.7 mW radiation. Hazard Probability Unlikely (E) Risk Assessment LOW... 

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