Risk assessment code

Unfortunately, most RAC matrices use scales that are so subjective and poorly defined as to be virtually meaningless. Granted that accurately placing exact numerical values on either severity or probability scales is difficult, these scales must be quantified to some extent to have any real value. The hurts a little—hurts a lot and maybe—maybe not approach to severity and probability scales, respectively, hardly provides the type of data required to support major risk acceptability decisions. 

Additionally, the severity scales are too restrictive. Certainly the loss of a single human life is tragic if the loss of a single life represents the upper extreme on the severity scale, however, how are hazards having the potential for killing dozens or hundreds or thousands of people in a single mishap to be 

Similarly, the probability scales are, in many instances, either broadly defined subjective word descriptions or, if quantitative, calculated guesses with no supporting calculations. In order to produce probability numbers, assumptions may frequently be necessary about failure rates, the number of units in the system, and the expected service life of the unit or the system. These 

Both severity and probability scales need to be expanded to provide more meaningful RACs. With many RAC matrices in use today, the opinions of ten different experts tend to produce ten different RACs. Reducing the reported level of risk by seeking a second opinion on the RAC associated with the risk becomes extremely tempting. 

If RACs are, in fact, going to serve as the drivers in the system and the basis for risk acceptance and resource allocation decisions, the numbers generated must have a positive correlation to the risk involved and to the resources required to control the hazard. A universal RAC matrix would provide a means of comparing relative risks associated with multiple projects, evaluating the allocation of funds, and determining the cost-effectiveness of various controls. Ideally, this universal risk assessment code matrix could provide an evaluation of risks in absolute as well as relative terms. Chapter 12 contains a proposed universal RAC matrix (Total Risk Exposure Codes). The use of a meaningful, quantified, expanded universal RAC matrix may represent a practical approach to probabilistic risk assessment. 

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Sa RA - Systems Analysis and Risk Assessment code - now part of IRRAS. 

Preliminary Hazard List Description. The incorporation of this information into a PHL entry is shown as Table I. This entry describes the nature of the hazardous event (column 1), why or how the hazard may result in a mishap (column 2), the effects on operating personnel, equipment, and the facility (column 3), the risk assessment code assigned to the uncontrolled hazard (column 4) and any comments the originator may have (column 5). 

A risk assessment code, using the agreed-upon risk assessment matrix. 

Failure modes and effects analysis is a systematic look at hardware, piece by piece, to determine how each piece could fail. The effects of each type of failure on the surrounding pieces and on the system or subsystem as a whole, and an assessment of the risk associated with each failure, commonly in terms of severity and probability, are expressed as a risk assessment code (RAC). 

A major objective of most of these analyses is to produce meaningful risk assessment data to aid in prioritizing hazards, allocating resources, and evaluating the acceptability of risks associated with these hazards. A common tool for assessing risk is the risk assessment code (RAC). The RAC is the number associated with a given level of severity and a given probability of occurrence as shown on a risk assessment matrix, with severity on one axis and probability on the other (Table 2-1). 

Even though some NASA documents reference the use of risk assessment codes (RACs), risk assessment for many NASA efforts is based on hazard level or criticality category. If risk assessment codes are used, they tend to use the hazard severity and probability categories and matrices from MIL-STD-882B. The NASA hazard levels are... 

Second, not only is there no standard risk assessment code (RAC) but also some people in this field maintain that there is no adequate risk assessment code. They are all so subjective as to be almost meaningless. 

At least two dozen different risk assessment code (RAC) matrices are in use. They all are based on severity on one axis and probability on the other, but the size and layout of individual matrices vary significantly. Some have severity on the vertical axis others have it on the horizontal axis. One makes the low numbers bad (an RAC of 1 indicates a high probability of a catastrophic accident), whereas the next uses a 1 to indicate a very remote probability of an insignificant loss. Some use RACs from 1 to 4 others use 1 to 16 still others use a combination of numbers, roman numerals, and/or letters (II to 4V or lA to 5D). 

Discuss briefly the shortcomings of the risk assessment codes currently in use. 

Very little real analysis is completed during the concept phase because analysis detail and data are generally not available. A preliminary risk assessment code (RAC) is determined, however, as part of the preliminary hazard list. This initial RAC is used to aid in determining the initial scope of the system safety effort and in the early evaluation of alternative designs and approaches. 

System Safety Requirements. Specify the system safety products to be produced, the risk assessment code matrix to be used, risk acceptability criteria, and residual risk acceptance procedures. 

RAC column The risk assessment code assigned to each uncontrolled hazard or undesired or unacceptable occurrence. 

Controlled RAC column Enter the risk assessment code after the recommended controls are in place. 

Data should be easy to access and sort. Sort fields could include type of part or product, manufacturer, cost, size, use, types of accidents or failures, geographic location, time, date, temperature, other environmental conditions, types of injuries, energy sources, dollar loss, analyst, project name, project number, system, subsystem, risk assessment code, and any other relevant comments that may aid in analysis of data. 

Different systems and approaches attempt to communicate risk information, most using various types of numerical scales. The most widely used is probably the risk assessment code. 

Even though this principle is the most widely used, numerous versions of risk assessment codes exist, as pointed out in Chapter 1. 

Hazard information is converted to risk information by evaluating the severity of potential accidents associated with the hazard and by evaluating the probability that the hazard could produce an accident. It is done by developing a matrix with severity on one axis and probability on the other, with a numeric code used to represent the risk associated with each hazard. This risk assessment code (RAC) is used to prioritize hazards and determine their acceptability. Hazard severity may be expressed quantitatively (for example, dollar loss or number of injuries), qualitatively (verbal descriptions), or as a combination (Table 11-1). 

The risk assessment code matrix shown in Figure 11-2 is typical of those used in military programs and very similar to the examples found in MIL-STD-882B. 

Figure 11-2 Risk assessment code matrix used in the facility system safety effort. It is typical of military programs and similar to the example matrices listed in MIL-STD-882B. (Source U.S. Army Facility System Safety Manual. Draft.)...

As pointed out in Chapter 4, deficiencies in the current risk assessment code systems represent one of the major problems facing the entire system safety effort. 

For all practical purposes, the risk assessment code is the driver in the system. The value of this code prioritizes the fixes and the management or command emphasis given to a particular problem. If these codes are not detailed enough to discriminate between very serious hazards and lesser hazards accurately, they are of little value. 

In any event, this information should be more meaningful, more useful, and more valuable to management than the traditional risk assessment code. 

Determine the risk associated with each potential unwanted energy flow and express this risk in terms of a risk assessment code (RAC). 

Column 4—RAC. Enter the risk assessment code associated with this particular unwanted energy flow. List a separate RAC for each potential target. 

Column 5—RAC or Hazard Category. Enter the risk assessment code (RAC) or hazard category for each failure listed in column 2. An RAC is recommended however, some organizations evaluate FMEA failure only in terms of severity or criticality. In any event, the risk assessment codes or hazard categories must be clearly defined, and their definitions must be included in the FMEA report and/or physically attached to the FMEA worksheets. 

Used originally as a reliability tool, the FMEA is now often used to identify and prioritize safety problems associated with hardware failures. This is usually done by including a risk assessment code (RAC) in the analysis (Table 14-1). (Note When a RAC or other method of quantifying is used to identify critical safety items, some organizations and analysts call the technique failure mode and effects criticality analysis [FMECA].)... 

The risk assessment code (RAC) matrix and the hazard severity and probability indices and definitions used in this study were taken from EMX-XXXX (the Facility System Safety Manual). 

Therefore, extreme value projection may be useful in calculation probabilities to be used for risk assessment codes or total risk exposure codes based on actuarial data. Extreme value projection can also be useful in communicating hazard information to management and may aid in drawing management attention to a problem before a serious accident occurs. 

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