Safe state

Although the traditional point of reference for safety interlock systems is a hard-wired implementation, a programmed implementation is an alternative. The potential for latent defects in software implementation is a definite concern. Another concern is that solid-state components are not guaranteed to fail to the safe state. The former is addressed by extensive testing the latter is addressed by manufacturer-supplied and/or user-supplied diagnostics that are routinely executed by the processor within the safety interlock system. Although issues must be addressed in programmable implementations, the hard-wired implementations are not perfect either. 

An interlock is a protec tive response initiated on the detection of a process hazard. The interlock system consists of the measurement devices, logic solvers, and final control elements that recognize the hazard and initiate an appropriate response. Most interlocks consist of one or more logic conditions that detect out-of-hmit process conditions and respond by driving the final control elements to the safe states. For example, one must specify that a valve fails open or fails closed. 

The basic approach is to direct the system to the safest operating level relative to people or the environment when any emergency condition is detected, including power loss. An important concept of process control safety is to have adequate redundancy to reduce unwanted shutdowns and maintain an adequate level of certainty that a safe state will result if a real emergency does occur. As far as possible, instruments should be of the fail-safe type. 

There are few chemical plants that are so forgiving that a control system or a safety interlock system is not required. Process engineers provide controls to assure product yield and quality and maintain safe operating conditions. This type of control system is a BPCS. The BPCS acts to alarm and moderate a high or low operating condition specified by the normal operating limits within the never exceed critical limits. The SIS is provided to shut down or otherwise place the process in a safe state if the BPCS fails to maintain safe operating conditions. A BPCS should not be used as the sole source of a process safety shutdown. 

One can thus safely state that NMR techniques have become flexible and valuable tools for characterizing industrial porous catalysts in length scales from nanometers to centimeters, and to correlate information on these scales, for... 

The rate of radiocarbon formation in the upper atmosphere depends on a number of factors, which include the intensity of the incoming cosmic radiation, the activity of the sun, and the magnetic field of the earth (the latter affects the way cosmic rays travel). It can be safely stated, however, that radiocarbon is formed at a steady rate that averages just about 2.4 atoms of radiocarbon per second for every square centimeter of the earth s atmosphere outer surface. 

Ion transfer across ITIES is easier to study than electron transfer so there is a greater body of experimental data. However, their interpretation is just as difficult. At the present time we can safely state ... 

Include provisions for detecting abnormal process conditions and bringing the process to a safe state before an emergency situation occurs (Safety Instrumented Systems). 

Introduction The chemical processing industry relies on many types of instrumented systems, e.g., the basic process control systems (BPCSs) and safety instrumented system (SIS). The BPCS controls the process on a continuous basis to maintain it within prescribed control limits. Operators supervise the process and, when necessary, take action on the process through the BPCS or other independent operator interface. The SIS detects the existence of unacceptable process conditions and takes action on the process to bring it to a safe state. In the past, these systems have also been called emergency shutdown systems, safety interlock systems, and safety critical systems. 

Define safe state, including safety and nonsafety actions. 

Cable trays outside of process areas or unit battery limits are normally not provided with either passive or active fire protection regardless of size. Small cable trays are usually not fire protected regardless of location when they provide service for ancillary equipment or for equipment designed to fail to a safe state on loss of power, control signal or communication. 

SIS Safety instrumented shutdown (SIS) systems have been installed on several units. These systems automatically remove feed and hydrocarbon from the process to place the unit in a safe state when a set of conditions that represent an unsafe operation is observed. 

For the fast reaction, if the feed is immediately stopped after a cooling failure has occurred the reactor reaches a safe state. Thus, the SBR is a practicable solution for this fast exothermal solution. 

We caution the reader that applying Carnot s analysis is based on the assumptions that the heat is available at temperature T and that the heat reservoir is infinite. This means that if we use the adiabatic flame temperature for T, we will end up with a maximum attainable efficiency, since the exchange of heat will inevitably lead to a reduction in the temperature of the reservoir. From our analysis, it is not clear whether we used an adiabatic flame temperature [11]. Note that the adiabatic temperature is the highest temperature that can be reached by the system if all the heat generated is used to elevate the flame temperature. However, we can safely state that at least 30% of the maximum work potential has been lost. We will return to this subtle point at a later stage, when we examine the combustion of natural gas. 

At PPG, Class 1 Prooftesting also covers 250 Safety Instrumented System loops in the PSM Safety Systems. A Safety Instrumented System (SIS) is composed of sensors, logic solvers, and final control elements for the purpose of taking the process to a safe state when predetermined conditions are violated. SISs are normally controlled by a PLC with the sole function of monitoring a process to insure operation is maintained within the safe operating envelope. 

Fortunately the observed deviations are not usually very large. When differences between the results of calculations and experimental measurements appear, it can not at present always be safely stated to what extent they are caused by variations in kt or by termination of, or by, primary radicals (non-ideality of polymerization). 

I-IX) is far from complete, we can safely state that alkaloids have potent deterrent or poisonous properties in herbivorous animals, and also affect bacteria, fungi, viruses, and plants. The next question will be whether all the adverse activities of alkaloids, which are often assayed in in vitro systems only, are meaningful in Nature. 

Will the system recover to a safe state after a power failure ... 

Are there safe states for operation (startup, shutdown, holds, normal running, emer-geney shutdown, maintenance) ... 

A risk analysis is then required to confirm these safety requirements can be met, that the medical device will not malfunction, and that a safe state is maintained in relation to patient health. For the insulin delivery system a safe state is a shut-down state where no insulin is delivered. Over a short period this will not pose a threat to the diabetic s health. ... 

Compositions which are used for fireworks are mixtures of various components and all the oxidizers dissolve in water. These compositions therefore are easily damaged by moisture. Sometimes this is useful for temporarily keeping a composition in a safe state, as in the wet process for example,sometimes however this can lead to a misfire. 

Endothermic Reactions An endothermic reaction process is generally easier to bring to a safe state if an out-of-control situation is detected. Discontinuing the heat input is usually the primary line of defense to stop the operation. In this regard, the endothermic reaction is inherently safer than an exothermic reaction. 

---