Class A accident

Class A accident—The resulting total cost of damages to government and other property in an amount of 1 million or more a DoD aircraft is destroyed or an injury and/or occupational illness results in a fatality or a permanent total disability. 

In a single year in the early 1980s the Israeli Air Force had about 30 class A accidents during training. (A class A accident involves the loss of a pilot, an aircraft, or damage in the amount of at least 1 million.) The Knesset (Israeli Parliament) called in the commander of the Air Force and told him that the country could not afford this and they had to do much better. 

Over a period of several years, through the finding and eliminating root causes, the incidence of class A accidents was reduced to near zero. 

Approximately 60% of all U.S. Naval Aviation-Class A accidents (i.e., the ones that caused death, permanent disability, or loss of 1 million) were the result of various human and organizational factors [19,20]. 

Uncertainly estimates are made for the total CDF by assigning probability distributions to basic events and propagating the distributions through a simplified model. Uncertainties are assumed to be either log-normal or "maximum entropy" distributions. Chi-squared confidence interval tests are used at 50% and 95% of these distributions. The simplified CDF model includes the dominant cutsets from all five contributing classes of accidents, and is within 97% of the CDF calculated with the full Level 1 model. 

Some definitions of safety criteria (IAEA Safety Criteria and EUR Requirements) specify a third class of accidents that lies between the two already mentioned. These include ... 

On the other hand, the Specific and Management branches are regarded as the two main branches in MORT (see Figure 2). Specific control factors are broken down in to two main classes a those related to the incident or accident (SAl), and b those related to restoring control following an accident (SA2). Both of them are under an OR logic gate because either can be a cause of losses. 

Frequency and severity data from accidents can help identify risks. A review of accident records and classes of accidents can help. Various statistical methods applied to accident data can reveal trends in losses and factors that contribute to accidents and injuries. Analyzing claims, such as worker compensation claims or customer claims against products, will help isolate factors associated with losses. 

The safety analysis should aim to quantify a plant safety margin and demonstrate that a degree of defence in depth is provided for this class of accidents. This would include such measures where reasonably achievable ... 

The first sub-class includes accidents that appear to persist, but are actually renewed (tajaddada) constant by a cause. The onfy example we are given of this type of accidents is motion in space. The notion of renewal here may seem to presuppose the atomistic conception of time espoused in classical kaldm, but is in fact borrowed from Avicenna (who, in turn, adapts it from the Mu tazila). Locomotion, according to Avicenna, is produced in the mobile constantly by the inclination that supervenes upon it This renewal of motion is not atomistic, but continuous locomotion is continuously renewed yatajaddadu "aid l-ittisdl), as Avicenna writes. On such accidents, al-Mas udi writes ... 

The second sub-class includes accidents that, of themselves, lack continued existence, but may be sustained in existence by a force qasr) applied con-... 

During the early 1970 s, W. G. Johnson (former General Manager of the National Safety Council) developed a more specialized version of Uie fault tree known as MORT (Management Oversi and Risk Tree) as an evaluative tool for safety professionals and their management. Its effectiveness has been veiibed in actual field trials. Its use is now mandatory within ERDA for the more severe classes of accidents. 

In its broadest sense, MORT is a formal disciplined logic that systematically relates and Integrates a wide variety of safety concepts. The effectiveness of the MORT system, with over eight years of deveiopment and test behind it, has been verified in actual field trials. Its use is now mandatory within the U.S Department of Energy for the more severe classes of accidents. 

In most cases, the approach to HWR licensing has been performance-based rather than prescriptive. That is, the regulator sets overall requirements on the classes of accidents to be considered, and on the public dose limits as a function of accident class, but leaves it up to the licensee to a large extent to determine how best to meet the requirements and limits. In particular most HWR regulators do not specify the design requirements in great detail, nor do they specify prescriptive assumptions on accident analysis methods. 

Melting of all or part of the core could only occur as a result of the cooling capacity dropping significantly below the rate at which power is being produced in the fuel. There are two classes of accidents which could cause this to happen these are the following ... 

In the event of a LOCA, the nuclear reaction in the core would be automatically cut off by the loss of the moderation associated with the coolant, while in the transient case the probability of failure of the shutdown systems is sufficiently low that continued operation at power is not a significant contributor to a core melt situation. For both classes of accident, therefore, the important requirement is the maintenance of a cooling capability sufficient to remove decay heat (see Table 12.7) from the reactor core. The emergency core cooling systems (ECCS) for the PWR and BWR are described below. 

Accidents (mishaps) are classified into three categories as delineated by the Department of Defense Instruction (DoDINST) 6055.7. These categories are Class A, Class B, and Class C, which are defined as follows ... 

Class B accident—The resulting total cost of damage is 200,000 or more, but less than 1 million. An injury and/or occupational illness results in permanent partial disability, or when three or more personnel are hospitalized for in-patient care (which, for accident reporting purposes only, does not include just observation and/or diagnostic care) as a result of a single accident. 

Class C accident—The resulting total cost of property damage is 20,000 or more, but less than 200,000 a nonfatal injury that causes any loss of time from work beyond the day or shift on which it occurred, or a nonfatal occupational illness or disability that causes loss of time from work or... 

A CSI is essentially the same as an SCI except that systems required to identify CSIs have additional statutory and regulatory requirements that the contractor must meet in supplying those CSIs to the government. For systems required to have a CSI list, HA and mishap risk assessment is used to develop that list. The determining factor in CSIs is the consequence of failure, not the probability that the failure or consequence would occur. CSIs include items determined to be life-limited, fracture critical, fatigue-sensitive, and so on. Unsafe conditions relate to hazard severity categories I and II of MIL-STD-882. A CSI is also identified as a part, subassembly, assembly, subsystem, installation equipment, or support equipment for a system that contains a characteristic, failure mode, malfunction, or absence of which could result in a Class A or Class B accident as defined by DoDINST 6055.7. 

According to Mr. Raz, the annual rate of class A training accidents in the Israeli Air Force was reduced from above 35 per year, during the 1970s and 1980s to fewer than 3 per year in the late 1990s. This low rate still continues today. 

Figure 5.4 was supplied by Mr. Raz. It depicts the decline in what they now call Class 5 accidents, which involve the loss of an aircraft or a pilot, or damage exceeding 1 million. It depicts the decline from over 30 incidents per year in 1980 to a level of zero in 2001 and 2002. Mr. Raz has asked that we not pubhsh numbers, but rather focus on the relative change, which is quite apparent. 

Systemic root causes involve a deficiency in a management system that, if corrected, would prevent the occurrence of a class of accidents. 

Figures 5.1-7 and 5.1-8 show the uncertainty in the probability of early containment failure conditional on the occurrence of three different classes of accident sequences for the plants analyzed in NUREG-1150. Containment bypass scenarios are not included in these figures, and the results are for internally initiated accidents only. The plant-specific mean frequency of the accident class is listed to the right of each uncertainty interval. For some of the plants (e.g., Zion and Surry) the best estimate of the conditional probability of early containment failure is quite small (about 1%) however, for all plants the uncertainty in the estimated likelihood of early containment failure is quite large. This uncertainty arises as a result of corresponding uncertainties in both the pressures and temperatures that would exist within the containments and the ability of the containments to withstand these pressures and temperatures. In addition, for several of the containments there is uncertainty regarding the mode (structural mechanism, location, size of opening, etc.) by which containment would fail.

---