Functional safety equipment

For mechanical systems (e.g. (a) and (b) above), it is important to ensure that, during maintenance, the safety functions of equipment are recognised. Otherwise, they may be replaced with unsuitable equipment. For instance, it is preferable for flow restrictors to use an orifice welded within a short length of pipe, so that it cannot easily be left out, rather than, an orifice plate that slips between pipe flanges. It is desirable to have some method of clearly indicating that such equipment has a safety critical function. 

Controls. Process consistency is a function of equipment and process repeatability. Design and manufacturing quality is also very important. All systems should be supplied with a control strategy that allows automatic cycling. Automatic operation improves consistency, safety and reliability, and reduces the labor content, assuring efficient and cost effective operation. 

Through these studies we have acquired considerable data on human exposure as well as experience in designing and conducting research to monitor real-life exposure of pesticide applicators. Exposure is relevant to human health only in relation to the dose taken into the body, its toxicity, and the rate of excretion. In our studies we have monitored no group nor individual whose dose approaches a level which could affect human health. Our studies have shown that exposure and dose are influenced materially by human attire and habits, type and function of equipment, and safety precautions such as protective clothing or washing soon after exposure to a concentrate. 

Other important causal factors and questions also were not addressed in the report such as why the level transmitter was not working so soon after it was supposedly fixed, why safety orders were so delayed (the average age of a safety-related work order in this plant was three months), why critical processes were allowed to operate with non-functioning or erratically functioning safety-related equipment, whether the plant management knew this was happening, and so on. 

Functional safety requirements of the process equipment Define hazard potential, perform Level Of Protection Analysis (LOPA)... 

The following discussions will be limited to a generalized or typical presentation reeaizlng that variations in equipment exist between reactors. However, where system concepts vary from reactor to reactor, each concept will be discussed. Instrumentation will be presented according to the classifications as defined in Section II-A (Page 11). Particular attention is given to the whole system. e. power supply, transducer, the instrument Itself, control function (safety circuit monitoring or readout device ) and pertinent comment. ... 

The first step in the calculation process is to properly identify the equipment required for each safety instrumented function. All equipment associated with a particular SIF must be classified into "primary" -equipment needed to provide the required protection against the identified hazard and "auxiliary" - equipment that provides useful functionality but not required to protest against the hazard. This classification is important because only primary equipment is included in the PFDavg analysis and the SFF analysis. 

Problem A set of non-redundant (hardware fault tolerance = 0) safety equipment is used to perform a safety instrumented function in continuous demand mode. Diagnostic time is given as one second. The following failure rate data is obtained when adding the failure rates of the categories of all components ... 

Even with approximate data, the methods began to show how designers could achieve higher levels of safety while optimizing costs. The safety verification calculations required by the new functional safety standards have shown designers how to design much more balanced designs. The calculations have shown many how to do a better job. But, failure rate and failure mode data for random failures on the chosen equipment is required. 

The concept of the "well designed system" was also presented in Chapter 3. A simplistic definition of such a system would be one where aU the techniques and measures presented in our functional safety standards to prevent systematic failures are followed. These techniques and measures are planned to significantly reduce the chance of a systematic fault to a tolerable level. Therefore, systematic failure rates caused by human error including failures due to installation errors, failures due to calibration errors and failures due to choosing equipment not suited for purpose are not included in the calculation. 

No safety feature or interlock of any equipment in the facility shall be disabled without written approval ofthe laboratory supervisor. Any operations which depend upon the continuing function of a critical piece of safety equipment, such as a fume hood, shall be discontinued should the equipment need to be temporarily removed from service for maintenance. Any such item of equipment out of service shall be clearly indicated with a signed Out of Service tag. Oiily the person originally signing the tag, or a specific, designated alternate, shall be authorized to remove... 

As can be seen, the two points of view are different and, while the current standard considers damage and collapse, there is also the need to protect a plant s functionality and prevent accidents. These concepts imply, in particular, the prevention of significant leaks of noxious gases and liquids, the absence of reactions and of uncontrolled and destructive phenomena and the functionality of the safety equipment (shut-down, cooling, containment and control). 

Safety is a line responsibility that is shared by the operators, facility supervisor, facility manager. Director, and Vice President. The staff is procedurally trained to understand and obey the Technical Safety Requirements (TSRs) of the facility. If plant conditions change such that TSRs are threatened by operations, experiments, equipment failures or external forces, then operations are immediately terminated to minimize the possibilify of a TSR violation and a potential unanalyzed or unsafe condition. The Hot Cell Facility Periodic Maintenance/ Surveillance Operating Procedure (SNL 1997c) requires periodic inspection and checkout of important safety equipment and safety system settings to minimize the chance of "undetected" degradation of safety equipment that could lead to a safety function failure. 

The knowledge-based system will be equipped with context help pointing to more important aspects of lEC 61508 and lEC 61511 as well as the methods used in SIL determination and verification based on relevant models and their parameters. Functional safety projects are electronically documented and printed out when required in the form of an overall project report or partial project report. 

Safety equipment should be inspected regularly (e.g., every 3 to 6 months) to ensure that it will function properly when needed. It is the responsibility of the laboratory supervisor or safety coordinator to establish a routine inspection system and to verify that inspection records are being kept. 

Periodically test and inspect emergency devices (e.g., safety showers and eyewash stations) and safety equipment (e.g., fire extinguishers, fire blankets, and first aid and spill control kits) to make sure they are functional. Inspectors need to verify that workers are using personal protection and safety equipment appropriately in their day-to-day work. 

First, functional safety is that part of overall safety that depends on a system or equipment operating correctly in response to its inputs. Neither safety nor functional safety can be determined without considering systems as a whole and the environment with which they interact. 

The historical development of this type of monitoring equipment goes from electromechanical units as the Lilly Controller via electronic units and standard-PLCs used together with basic sensors and actuators to todays requirements to use electronic/programmable systems together with sensors and actuators that all are designed according a Functional Safety standard. 

Now define p,- as the value of ji making (3.7) hold as an exact equality. Assuming that p, the firm s safety equipment efficiency parameter, is continuously distributed firms with p greater than p,-provide levels of workplace safety greater than or equal to l-tt,- while firms with p lower than p,- provide less safety. Looking across all levels of safety we can identify y-1 values of p that sort firms into the J possible submarkets with each value depending on all wage rates, injury rates, and parameters of the expected profit function. 

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