Multiple layers of protection

In general, the safety of a process relies on multiple layers of protection. The first layer of protection is the process design features. Subsequent layers include control systems, interlocks, safety shutdown systems, protective systems, alarms, and emergency response plans. Inherent safety is a part of all layers of protection however, it is especially directed toward process design features. The best approach to prevent accidents is to add process design features to prevent hazardous situations. An inherently safer plant is more tolerant of operator errors and abnormal conditions. 

While nuclear power plants use multiple layers of protection from the radioactive particles inside the reactor core, a serious accident can cause the release of radioactive material into the environment. It is not a nuclear explosion, because the uranium fuel used in a nuclear power plant does not contain a high enough concentration of U-235. For an explosion to occur, the uranium fuel inside the reactor would have to be enriched to about 90% U-235, but it is only enriched to about 3.5%. 

The concept of multiple layers of protection (barriers) has widespread support throughout the chemical processing industry. By providing sufficient layers of protection against an accident scenario, the potential risk associated with that accident can be avoided or at least reduced. For a given scenario, only one layer must work successfully for the consequence to be prevented. However, since no layer is perfectly effective, multiple layers of protection must be provided to render the risk of the accident tolerable. 

Multiple layers of protection are a concept incorporated in the American Chemistry Council Process Safety Code of Management Practices. ) Management Practice number 15 endorses sufficient layers of protection through technology, facilities, and personnel to prevent escalation from a single failure to a catastrophic occurrence. This approach can be applied to multiple system root causes when the investigation team evaluates... 

Johnson, PM. and Willows, A.O.D., Defense in sea hares (gastropoda, opisthobranchia, anaspidea) multiple layers of protection from egg to adult, Mar. Fresh. Behav. Physiol., 32, 147, 1999. 

The hot work permit has multiple layers of protection and might involve several people during the issue of a hot work permit. One person might wear two hats and assume the tasks and responsibilities of two people involved in the permitting process. The responsibilities of those involved are ... 

DOE Order 420.1, Facility Safety, requires the detailed application of that order s requirements to be guided by safety analyses that establish the identification and functions of safety (safety class and safety significant) structures, systems, and components (SSCs) for a facility and establish the significance of safety functions performed by those SSCs. It specifies that nuclear facilities shall be designed with the objective of providing multiple layers of protection to prevent or mitigate the unintended release of radioactive materials to the environment. The safety analyses must consider facility hazards, natural phenomena hazards, and external man-induced hazards. Paragraph 4.4.1 requires safety analyses for hazardous facilities to include the ability of SSCs and personnel to perform their intended safety functions under the effects of natural phenomena. DOE O 420.1 (DOE 1995) incorporates requirements from the cancelled DOE Orders 5480.28, 5480.7A, and 6430.1A(DOE 1993). 

It is imperative that there are multiple layers of protection against fire. If the choice is to only rely on one, there is a very good chance that people will die. For instance, the Seton Hall University dormitory fire that killed three and injured more than fifty students is an example of what happens when a school relies on one means of protection. 

A natural extension of the methodology should address the cost-optimal designer s decision making in case of multiple layers of protection as well as safety systems whose safety functions share components. 

In modern industrial plants, process safety relies on the principle of multiple layers of protection (AIChE, 1993, 2001 ISA, 1996). A typical configuration is shown in Figure 10.1. Each layer of protection consists of a grouping of equipment and/or human actions. The layers of protection are shown in the order of activation that occurs as a plant incident develops, with the most effective layers used first. The basic concept is that an incident should be handled at the lowest possible layer. In the interior of the diagram, the process design itself provides the first level of protection. The next two layers consist... 

Security layers of protection Also known as concentric rings of protection, a concept of providing multiple independent and overlapping layers of protection in depth. For security purposes, this may include various layers of protection such as countersurveillance, counterintelligence, physical security, and cyber security. 

Layers of protection Multiple, redundant, or diverse safeguards to prevent an incident from occurring regardless of the initiating event or the performance of any single safeguard. 

Consumption of unsaturated polyesters in the marine industry consists of broad usage for hulls, decks and numerous small parts such as hatch and engine covers. Hulls and decks are generally produced with unsaturated polyester resins and multiple layers of fiberglass cloth knits and chopped fibers. Most marine applications require the use of unsaturated polyester resin gel coats for exterior appearance and for protection from the elements. 

In chemical industry infrastructure security, protection in depth is used to describe a layered security approach. A protection-in-depth strategy uses several forms of security techniques and/or devices against an intruder and does not rely on one single defensive mechanism to protect infrastructure. By implementing multiple layers of security, a hole or flaw in one layer is covered by the other layers. An intruder will have to intrude through each layer without being detected in the process—the layered approach implies that no matter how an intruder attempts to accomplish his goal, he will encounter effective elements of the physical protection system. 

For example, as depicted in figure 9.1, an effective security layering approach requires that an adversary penetrate multiple, separate barriers to gain entry to a critical target at a chemical industry facility. As shown in figure 9.1, protection in depth (multiple layers of security) helps to ensure that the security system remains effective in the event of a failure or an intruder bypassing a single layer of security. 

A unique feature of the Foster Wheeler SCWO reactor is its full-length transpiring-wall liner, shown in Figure 4-2. Foster Wheeler claims that this liner design protects the reactor walls from corrosion and salt deposition. The reactor liner is fabricated from multiple layers of Inconel 600 assembled in sheets of what the technology provider refers to as platelets to produce transpiration pores. Deionized water is added to the SCWO reactor through transpiration pores in the liner... 

The design of most process plants relies on redundant safety features or layers of protection, such that multiple layers must fail before a serious incident occurs. Barrier analysis ) (also called Hazard-Barrier-Target Analysis, HBTA) can assist the identification of causal factors by identifying which safety feature(s) failed to function as desired and allowed the sequence of events to occur. These safety features or barriers are anything that is used to protect a system or person from a hazard including both physical and administrative layers of protection. The concepts of the hazard-barrier-target theory of incident causation are encompassed in this tool. (See Chapter 3.)... 

On the left (A) is a profile of the human brain, and on the right, a magnified view (B) of a slice through the brain as indicated by the dotted line. The anatomy of the brain consists of two hemispheres, each covered with multiple layers of important cells known as the cerebral cortex. White matter, which consists of wiring —projections from one cell to another—lies beneath the cerebral cortex, along with some groups of cells that perform various functions. The ventricles are cavities through which runs a substance called cerebrospinal fluid, which helps protect and cushion the delicate structures of the nervous system. 

Once the precautions that are needed to control exposures are determined, the next step is to compare the level of controls needed against what controls are already in place. There frequently are multiple control strategies that will minimize the potential for exposure. The determination of which control strategy is the best to use is determined by the hierarchy of control principle. Our particular approach to managing risk is to use this hierarchy to evaluate possible risk management approaches for a specific project in conjunction with a modified layer of protection analysis (LOPA) approach.5... 

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