Loss-of-control accidents

Objective To prevent loss of control accidents on downgrades by proper brake system maintenance and by developing the skills and knowledge needed to safely negotiate a... 

Objective To prevent loss of control accidents due to tire failure. 

Suitable entry path curvature (70 100 m) is the most important safety aspect of roundabout design. A radius of less than 70 m leads to loss-of-control accidents on the approach to the roundabout. 

Entry angles less than 20° lead to fail-to-give-way and rear-end-shunt accidents. High entry angles over 60° lead to sideswipe and loss-of-control accidents. For safety, the ideal entry angle is 30°. 

The subsequent step is to identify the various scenarios which could cause loss of control of the hazard and result in an accident. This is perhaps the most difficult step in the procedure. Many accidents have been the result of improper characterization of the accident scenarios. For a reasonably complex chemical process, there might exist dozens, or even hundreds, of scenarios for each hazard. The essential part of the analysis is to select the scenarios which are deemed credible and worst case. 

Tweeddale (Tweeddale, 1995) identified two general sorts of deviations, i.e. hard and soft deviations. He identifies hard deviations as malfunctioning equipment, and soft deviations as faults in the system or procedures. In this thesis these definitions are slightly modified to cover all deviations identified in the operational process preceding and directly related with an accident. Hard deviations are defined as the actual loss of containment or demonstrable loss of control, e.g. small leakages, overpressure, override of control systems, etc. Soft deviations refer to indications of possible deviations, but cannot be demonstrated by actual facts, e.g. operator complaints, deficiencies of maintenance activities, or bad housekeeping activities, etc. 

When dealing with highly exothermic reactions, process industries have long-established techniques for safe processing, often by slowing down such reactions, to a rate where heat evolution can be matched by the limited mass and heat transfers available in conventional reactors. Nevertheless, many serious accidents with exothermic reactions can be counted. A larger reactor requires careful calculation of potential heat flows, due to the high potential risks related to run-away reactions, loss of control and containment. 

Flight crews are the last defence against accidents such as controlled flight into terrain (CFIT), approach-and-landing accidents (ALA) and loss of control (LOG) incidents. Unfortunately skill, vigilance and conscientiousness - while essential for safety - are insufficient to prevent error -specially when crew are interrupted, when preoccupied with one of several concurrent tasks, or when forced to defer an action out of its normal sequence. 

AR303 1.7 Control of combustible gas concentrations in containment following a loss of coolant accident,... 

Criterion 19 - Control room. A control room shall be provided from which actions can be taken to operate the nuclear power unit safely under normal conditions and to maintain it in a safe condition under accident conditions, including loss-of-coolant accidents. Adequate radiation protection shall be provided to permit access and occupancy of the control room under accident conditions without personnel receiving radiation exposures in excess of 5 rem whole body, or its equivalent to any part of the body, for the duration of the accident. Equipment at appropriate locations outside the control room shall be provided (1) with a design capability for prompt hot shutdown of the reactor, including necessary instrumentation and controls to maintain the unit in a safe condition during hot shutdown, and (2) with a potential capability for subsequent cold shutdown of the reactor through the use of suitable procedures. 

D Radiological Consequences of a Design Basis Loss-of-Coolant Accident Leakage From Main Steam Isolation Valve Leakage Control System (BWR)... 

The HPI system at TMI-2 correctly came into operation because the system was undergoing a loss of coolant accident (LOCA) because of the stuck open relief valve. But at the time, the operators did not know that yet. They had neither diagnosed a LOCA nor its cause, because the control room pressurizer water level instrumentation indicated a level that was higher than normal. 

The control room instrumentation indicated a loss of coolant accident in progress. The indication of... 

The analysis of second order interdependencies and interdependencies further out in the chain of events or consequences can be analyzed much the same as the first order interdependencies. This means that we may reveal new location-specific interdependencies fiwm the functional interdependencies, and also events that should be further investigated, e.g., as an accident scenario itself In Figure 4, we see that the roads can be affected if there is a loss of ICT services. This is due to a possible loss of control with traffic lights, which then may cause traffic jams. In addition, no railway transport may increase the road traffic further. Hypothetical speaking, a traffic jam may cause a bridge to collapse due to overload, which may indicate location-specific interdependencies between road transport and the bridge. However, in this example, we focus on the functional interdependencies resulting fiwm the first location-specific interdependencies. 

March 28, 1979, Three Mile Island, PA. One of the nuclear power plants on this island in the Susquehanna River near Harrisburg, PA, experienced a loss-of-coolant accident. The event involved many complex issues. One class of problems involved the design of displays and controls in the plant control room. 

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