Hazard studies specification

Routine genotoxicity tests are not designed in order to derive no-effect levels. However, the magnitude of the lowest dose with an observed effect (i.e., the LOEL) may, on certain occasions, be a helpful tool in the hazard assessment. Specifically, it can give an indication of the potency of the test substance. Modified studies, with additional dose levels and improved statistical power may be useful in this regard. 

Software Design and Program Specification Design Review (inch Hazard Study)... 

Studies have indicated that the alloys used in the Ni/metal hydride batteries pose less of an environmental risk versus the Ni/Cd or Pb/acid systems (26). However, some legislation, e.g., the EC Directive on Hazardous Waste, specifically includes some of the materials used in these batteries (Ni and Co). In addition, several other heavy metals, e.g., rare earths, are used in some of the alloys. It remains to be seen how, or if, these metals will be regulated. 

In the previous chapter, it was established that in industry, plant hazards can cause harm to property (plant—machinery, asset), people, or the environment. So, it is important to develop some means of analyzing these and come up with a solution. Unfortunately, it is not as straightforward as it sounds. There are plenty of plant hazard analysis (PHA) techniques and each of them has certain strengths and weaknesses. Also each specific plant and associated hazard has specific requirements to be matched so that hazard analysis will be effective. In this chapter, various hazards (in generic terms) will be examined to judge their importance, conditions, quality, etc. so that out of so many techniques available for PHA it is possible to select which one is better (not the best because that needs to be done by experts specifically for the concerned plant) suited for the type of plant. So, discussion will be more toward evaluation of PHA techniques. Some PHA is more suited for process safety management (PSM) and is sometimes more applicable for internal fault effects [e.g., hazard and operability study (HAZOP)]. In contrast, hazard identification (HAZID) is applicable for other plants, especially for the identification of external effects and maj or incidents. HAZID is also covered in this chapter. As a continuation of the same discussion, it will be better to look at various aspects of risk analysis with preliminary ideas already developed in the previous chapter. In risk analysis risk assessment, control measures for safety management systems (SMSs) will be discussed to complete the topic. 

In June 1966, MIL-S-38130 was revised. Revision A to the specification once again expanded the scope of the SSP by adding a system modernization and retrofit phase to the defined life-cycle phases. This revision further refined the objectives of an SSP by introducing the concept of maximum safety consistent with operational requirements. On the engineering side, MIL-S-38130A also added another safety analysis the Gross Hazard Study (now known as the Preliminary Hazard Analysis). This comprehensive qualitative hazard analysis was an attempt to focus attention on hazards and safety requirements early in... 

In France, the reference law for seismic hazard studies is the RFS 2001-01. It provides the details describing the methodology specifically for seismic hazard analysis. The RFS 2001-01 is based on the deterministic approach, the most commonly used methodology in the seventies and eighties. The rule is based on a definition of the characteristics of Maximum Historically Probable Earthquakes considered to be the most penalizing earthquakes liable to occur over a period comparable to the historical period, or about 1,000 years. Secondly, it defines the Safe Shutdown Earthquakes . In the last few years the probabilistic approach has been used and accepted for the reevaluations of the seismic hazard of existing sites. 

As we have seen specification errors contribute a large proportion of safety system failures. Recognizing and imderstanding the safety problem to be solved is the first essential step in avoiding this problem. This in turn requires that we imderstand the nature of hazards and the contributing factors. Hence the emergence of systematic hazard study methods. 

This chapter takes a closer look at those aspects of hazard studies that have a bearing on the development and specification of safety instrumented systems. It is important to understand that in general, hazard studies are a part of the overall task of safety, health, and environment management for any industrial activity, particularly in large industrial plants. Functional safety is just one part of the safety management task and hence the lEC functional safety standard supports some of the tasks of safety management but does not cover the overall task. 

We first need to be aware of the essentials of the hazard study methods. Then we shall look at how best to interface hazard studies to the SLC activities necessary to generate a safety requirements specification. 

This figure shows how the lEC and ISA safety life cycle models for safety instrumented systems correspond to the established process safety life cycle models for hazard studies. The point of departure for the SIS life cycle is ideally at the end of hazard study 3 when the safety requirement s specification has been finalized. 

Once the general philosophy for prevention and mitigation has been established the hazard study team can follow up with more specific proposals. Typical key measures are listed here. 

Sometimes a hazard study team is tempted to prescribe an apparently obvious safety function for protection against a hazard. The instrument engineer should be careful to ensure that the safety function requirements are properly defined and thought out before agreeing to proceed with the solution. This is an advantage of developing a proper safety requirements specification, as we shall see in Chapter 4. 

The new safety life cycle is also required to identify specific hazards and risks in the context of the EUC, the EUC control system and all other external factors. Everything that the SLC needs for stages 2, 3 and 4 is obtainable via the hazard 2 study. Therefore, it may be helpful at this point to draw up an activity model to show how we can link up the SLC phases and the hazard studies to save everyone on a project team from a lot of duplicated effort. 

Armed with the above information the instrument engineer should be in a position to generate a preliminary estimate of performance and cost for each specific safety function requested by the hazard study team. The contents of the report back estimate are suggested here. 

The information gathered for the preliminary estimate is the same as that required to generate the safety requirements specification for the next stage of the SLC. Hence, if the hazard study team accepts the initial proposals fi-om the instrument engineer the next stage of the SLC can proceed. 

We conclude that hazard studies do most of the work needed for the safety life cyele. This work must be done to provide a valid way forward into the next phase, which is the safety requirements specification. 

The study team initially reviews actions brought forward fi om hazard study 1, and clarifies key principles of operation, which will assist in canying out hazard study 2, and which should be included in the project specification. 

Having carried out hazard study 2, the Basis for Safety , including health and environmental aspects, may be established and recorded in the project specification. 

This section should contain or refer to the project specification, the flow sheet and other documentation that was studied, and essential correspondence and information relating to hazard study 2. 

As the design of the plant and the control system progresses the details available from the fimctional specification of the control system will permit a more detailed hazard study just as is the case with the process hazard study. ICI and the AECI HAZOP manual suggest a detailed checklist procedure is then applied in a study team format to cover all the potential hazards. 

Our first task is to make sure we have some continuity from the previous material on hazard studies since it is the transition from hazard study to safety requirements specification that is so critical to the quality of the SIS solutions. We shall look at the development phases where the overall safety requirements are defined and then risk reduction tasks are allocated to SIS and non-SIS contributors. The development process leads to the actual SRS for the safety system that is to be designed and installed. 

Fig 4.2 describes the activities involved in progressing from the hazard study stage through to the completion of the detailed safety requirements specification. The development of the SRS is an iterative process carried out by the instrument engineer in co-operation with the plant design team and any associated safety specialists. Most of the information required for the SRS flows from the hazard analysis stages as we have seen in Chapter 3. 

In preparation for the specification of overall safety requirements lEC safety life cycle phase 4. The hazard study 2 is often used to propose the safety ftmctions diat will be incorporated into phase 4 after analysis.)... 

Example The combustion process in large vapor clouds is not known completely and studies are in progress to improve understanding of this important subject. Special study is usually needed to assess the hazard of a large vapor release or to investigate a UVCE. The TNT equivalent method is used in this example other methods have been proposed. Whatever the method used for dispersion and pressure development, a check should be made to determine if any govern-mentaf unit requires a specific type of analysis. 

The cost of performing the hazard identification step depends on the size of the problem and the specific techniques used. Techniques such as brainstorming, what-if analyses, or checklists tend to be less expensive than other more structured methods. Hazard and operability (HAZOP) analyses and failure modes and effects analyses (FMEAs) involve many people and tend to be more expensive. But, you can have greater confidence in the exhaustiveness of HAZOP and FMEA techniques—their rigorous approach helps ensure completeness. However, no technique can guarantee that all hazards or potential accidents have been identified. Figure 8 is an example of the hazards identified in a HAZOP study. Hazard identification can require from 10% to 25% of the total effort in a QRA study. 

This is important information that describes the site and provides workers, visitors, and other personnel with pertinent site information. In addition to studying job specifications, contracts, and talking with project management, the author(s) should develop a detailed operating history of the site. The history is useful when determining potential site hazards. The type of information that can typically be located includes ... 

The human factors audit was part of a hazard analysis which was used to recommend the degree of automation required in blowdown situations. The results of the human factors audit were mainly in terms of major errors which could affect blowdown success likelihood, and causal factors such as procedures, training, control room design, team communications, and aspects of hardware equipment. The major emphasis of the study was on improving the human interaction with the blowdown system, whether manual or automatic. Two specific platform scenarios were investigated. One was a significant gas release in the molecular sieve module (MSM) on a relatively new platform, and the other a release in the separator module (SM) on an older generation platform. 

Chapter 3 Health Effects Specific health effects of a given hazardous compound are reported by type of health (death, systemic, immunologic, reproductive), by route of exposure, and by length of exposure (acute, intermediate, and chronic). In addition, both human and animal studies are reported in this section. 

Case Studies in Environmental Medicine Taking an Exposure History—The importance of taking an exposure history and how to conduct one are described, and an example of a thorough exposure history is provided. Other case studies of interest include Reproductive and Developmental Hazards Skin Lesions and Environmental Exposures Cholinesterase-Inhibiting Pesticide Toxicity and numerous chemical-specific case studies. 

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