Failure process control engineering

Process Controls Engineers (continued) Equipment process capability Critical parameters process controls defined and reviewed Test equipment capability Review reaction plans for process failures... 

The task of the process control engineer then centered on establishing a control strategy to ensure stable dynamic performance and to satisfy product quality requirements. These objectives must be met in the face of potential disturbances, equipment failures, production rate changes, and transitions from one product to another. 

After explaining in the preceding chapter the control of processes by means of process control engineering equipment, subsequently safety devices are treated. They should become effective if the process control engineering measures should fail. Since processes take place inside enclosures (vessels, pipework etc.) the objective is to avoid the loss of their integrity (loss of containment, LOC). An important reason for such a loss is a pressure which lies above the failure pressure of the enclosure. This can, for example, result from component failures. Frequently increased pressure is accompanied by increased temperature, which lowers the load limits of materials and hence their failure pressure. Further reasons for a loss of integrity of enclosures are fires and explosions which cause pressure and/or temperature increases. 

The project Human Error in the Process Industry within the Ergonomics Section of the Technology Work Department at the Graduate School of Industrial Engineering and Management Science was started in 1985. In order to get acquainted with the world of chemical process control two exploratory investigations were carried out in the first two years at Dutch chemical companies. This led to the development of a prototype classification model of system failure (see Chapter 5 for the most recent version). 

Table 17.1 shows the aspects of process safety for which actions are required by OSHA in Title 29 of the Code of Federal Regulations, Part 1910, Section 119 (29 CFR 1910.119) [1] and by the EPA in Title 40 of the Code of Federal Regulations, Part 68 (40 CFR 68) [2]. This Chemical Process Safety section concentrates on the engineering aspects of Process Safety Information —on the consequences of failure of engineering and administrative controls and the qualitative evaluation of a range of the possible safety and health effects of failure of controls requirements of the OSHA and EPA Process Hazards Analysis and the Off-Site Hazard Assessment. ... 

Reliability, Maintainability, and Quality Control. Inclusion of these organizations in the system safety process, from concept through disposal, will aid in the identification of safety-critical components for reliability analysis. A failure mode(s) and effect(s) analysis (FMEA), as well as other common reliability models, can be used to identify critical and noncritical failure points. The quality assurance element can be extremely usefid in the overall system safety process. Quality engineers should participate in the inspection of safety-critical components, serve on certification boards, audit any corrective-action requirements, and identify any safety impacts associated with implementation of such requirements. 

The management of process plant engineering resource costs and schedule durations is frequently problematical and occasionally disastrous. Often the problems stem from a technical error, or series of errors, which are discovered too late and require remedial action. Equally often, however, the problems stem from management failure, that is, from failure to plan the work and control its execution according to the plan. The plan may be unachievable because the project team is not sufficiently competent to meet the challenge, or because irresistible (or insufficiently resisted) external factors dictated an over-optimistic commitment. 

Large, complex facilities that process fissile materials present a special challenge to criticality safely specialists. As fissile materials pass through the process chain, failure of controls in one area may propagate to other areas. One such facility is the Transuranic Waste Treatment Facility (TWTF) planned for the Idaho National Engineering Laboratory (INEL). This paper discusses the use of fault tree methods in the criticality assessment of such facilities by the example of the TWTF. 

Layers of protection There are many independent layers of protection provided in the control measure in addition to the basic process control system. These layers of protection make the control measures more robust. Fig. 11/4.5.4-1 may be referred to for more detail. Detailed discussions are available in Chapter V. Common mode failure Common mode failure refers to the failure of more than one control system on account of a common cause, which underlines the importance of independent layers of protection. However, common cause can affect both engineering and administrative controls. So, while considering the adequacy of control measures used for risk prevention/reduction/mitigation, etc. it is necessary and important to see that all such control measures are not only independent but also do not suffer from common mode fculure—discussed in later part of the book. 

Functional safety engineering involves identifying specific hazardous failures whieh lead to serious consequenees (e.g., death) and then establishing maximum tolerable frequency targets for each mode of failure. Equipment whose failure contributes to eaeh of these hazards is identified and usually referred to as safety related. Examples are industrial process control systems, proeess shut down systems, rail signaling equipment, automotive controls, medical treatment equipment, etc. In other words, any equipment (with or without software) whose failure ean eontribute to a hazard is likely to be safety related. 

Once the critical nodes and links have been identified the first question is how can the risk be mitigated or removed At its simplest this stage should involve the development of contingency plans for actions to be taken in the event of failure. At the other extreme, re-engineering of the supply chain may be necessary. Where possible statistical process control should be used to monitor the critical stages along the pipeline. 

Most or the incidents described were the result or not rollowing good engineering practice. Some violated the law, and many more would if they occurred today. In the United States, they would violate OSHA 1910.147 (1990) on The Control of Hazardous Energy (Lock Out/Tag Out) and the Process Safety Management (PSM) Law (OSHA 1910.119, in force since 1992). which applies to listed chemicals above a threshold quantity. The PSM Law requires companies to follow good engineering practice, codes, industry consensus standards, and even the company s owm standards. OSHA could view failure to follow any of these as violations. 

---