Protection system defeated

Armor. Sihcon carbide is used as a candidate in composite armor protection systems. Its high hardness, compressive strength, and elastic modulus provide superior baUistic capabihty to defeat high velocity projectile threats. In addition, its low specific density makes it suitable for apphcations where weight requirements are critical (11). 

Secondary containment systems are best described as passive protective systems. They do not eliminate or prevent a spill or leak, but they can significantly moderate the impact without the need for any active device. Also, containment systems can be defeated by manual or active design features. For example, a dike may have a drain valve to remove rain water, and the valve could be left open. A door in a containment building could be left open. 

At several stages in the events leading to the accident, the operators defeated a trip signal or other protection system because it seemed likely to interfere with the test. Eventually, a significant part of the system had been disabled. Similarly, the operator ran the control rods much further out from the core than his operating rules permitted. These actions... 

Modifications in the reactor protection system to enable defeating interlocks or overriding protective trips... 

The design shall be such as to minimize the likelihood that operator action could defeat the effectiveness of the protection system in normal operations and expected operational occurrences, but not to negate correct operator actions in design basis accidents. 

Ideally, in a perfect world, all chemical facilities would be secured in a layered fashion (aka the barrier approach). Layered security systems are vital. Using the protection in-depth principle, requiring that an adversary defeat several protective barriers or security layers to accomplish its goal, chemical industry infrastructure can be made more secure. Protection in depth is a term commonly used by the military to describe security measures that reinforce one another, masking the defense mechanisms from the view of intruders, and allowing the defender time to respond to intrusion or attack. 

Although the use of personal protective equipment is common and necessary in many occupational situations, it is the least effective method to deal with hazards and risks. Systems put in place for their use can be defeated easily. In the design process, one of the goals should be to reduce reliance on personal protective equipment to a practical minimum. 

The features of fire protection are essential components in the overall safety systems included in the school built environment. They must not be defeated or altered in anyway, or the risk of their failure during a fire event is high and the risk of injury or death is increased. A program of inspection, testing, maintenance, and service along the manufacturers recommendations and local fire codes will help to ensure that these systems will operate appropriately in the event of a fire. Documentation of these activities should be maintained in order to record these activities and prove compliance with accepted standards. Visual inspections should be done periodically to check for any conditions that may adversely affect the systems described in this chapter, and trained personnel should be consulted if questions arise. 

CCFs often dominate the unreliability of redundant systems by virtue of defeating the random coincident failure feature of redundant protection. Consider the duplicated system in Figure 5.2. The failure rate of the redundant element (in other words the coincident failures) can be calculated using the formula developed in Table 5.1, namely 2X MDT. Typical failure rate figures of 10 per million hours (10 per hr) and 24hrs down time lead to a failure rate of 2 x 10 x 24 = 0.0048 per million hours. However, if only one failure in 20 is of such a nature as to affect both channels and thus defeat the redundancy, it is necessary to add the series element, shown as X2 in Figure 5.3, whose failure rate is... 

They use existing estimates of restraint effectiveness in crashes and a fixed distribution of traffic accidents as do Arnould and Grabowski. For safety belt use, however, they use a different technique. They asked a panel of 5 specialists in occupant-crash protection what they thought the percentage of occupants belted in crashes for fleets of cars with detachable passive belts would be. The composite median usage was 17 percent with a composite lower boimd (.1 fractile) of 10 percent and a composite upper level (.9 fractile) of 35 percent. The panel of specialists was asked the same question for discourage-defeat passive belts which are not easily detached. The composite median usage for the more coercive belt system was 43 percent with a lower bound of 15 percent and an upper bound of 60 percent. 

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