Process hazards High Level

A major process hazard (High Level Severity - Subsection 6.5, Appendix J1) is defined as an event or process upset which has the potential for resulting in one or more of the following consequences ... 

During the design process, these high-level hazards will be refined as the design alternatives are considered. Chapter 9 provides more information about the refinement process and an example. 

Applicability Most hazardous waste slurried in water can be mixed directly with cement, and the suspended solids will be incorporated into the rigid matrices of the hardened concrete. This process is especially effective for waste with high levels of toxic metals since at the pH of the cement mixture, most multivalent cations are converted into insoluble hydroxides or carbonates. Metal ions also may be incorporated into the crystalline structure of the cement minerals that form. Materials in the waste (such as sulfides, asbestos, latex and solid plastic wastes) may actually increase the strength and stability of the waste concrete. It is also effective for high-volume, low-toxic, radioactive wastes. 

Examine all process parameters. Parameters (e.g., pressure, temperature, flow rate, level, pH) that are controlled or measured in a process are good indicators of possible process hazards. Process parameters should be examined for all modes of operation, independent of process chemicals, because some hazards exist that do not involve the chemicals. For example, if a process uses high-pressure steam, then both thermal energy and pressure-volume energy hazards exist even though steam is non-toxic, non-flammable, and non-reactive with most materials. 

The facility is subjected to a process hazard analysis commensurate to the level of hazard the facility represents (i.e., Checklist, PHA, HAZOP, What-If review, Event Tree, FMEA, etc.). The results of these analyses are fully understood and acknowledged by facility management. Where high risk events are identified, quantifiable risk estimation and effects of mitigation measures should be evaluated and applied if productive. 

The best example of this is wastes that are classified based solely on the nature of the generating process or facility e.g., high-level radioactive waste, chemical wastes from certain industries), irrespective of the content and concentration of hazardous substances. This results in resources being used unnecessarily on lower-risk situations when they could be better applied to higher-risk situations (hazardous waste disposal or otherwise). For example, billions of dollars have been spent in managing... 

However, some important waste classifications are based on attributes not intrinsic to the waste. A prime example is waste that is classified based on its source (process or organization), such as high-level radioactive waste and many listed hazardous chemical wastes. The undesirable effects of this are summarized previously and are not repeated here. 

High-level defense waste solutions resulting from plutonium recovery and waste processing activities currently are stored in mild steel-lined concrete tanks located underground at the U.S. Department of Energy s Hanford Site. Low radioelement solubility and extensive radioelement sorption on surrounding sediment help maintain isolation of hazardous radionuclides from the biosphere in the event of tank failure. 

As the role of the consultant is to lead and guide the review process it could be stated that he might not need to be particularly familiar with the types of facilities under review. This is not true since some knowledge of the basic hazards of the facility and substances involved are needed in order to provide adequate importance to points raised in the review. For example mercury levels in produced gas streams for production systems may not be of concern, but in refining systems the high levels of mercury caused extensive corrosion problems. Experienced leaders can expedite the review process by knowing important issues to highlight and vice-versa. 

It has been found that the What-If style of process hazard analysis is a convenient method to use for a "simple" facility. For simple facilities, the detailed HAZOP approach has been found to be tedious and just as productive as a What-If method. The What-If approach stimulates generation of new ideas and discussion to cover issues associated with the items under review, as well as addressing generic issues. The specific HAZOP review is not necessary when the process is simple and well understood by the reviewing team. The team can readily review the major items of concern by asking What-If questions such as what happens when a pump fails, without relying on itemized and detailed variations of a process condition by the HAZOP method, such as high level, low pressure, etc. 

The current lack of knowledge of chemical risks severely hampers the substitution of a hazardous substance by a substance or process that provides a lower degree of risk [183, 189]. Legislation has even resulted in the substitution of one dangerous substance for one that later proves to also present high-level risks. Prime examples include... 

Risk assessment is a scientific process whereby the level and nature of the risk is determined. If there is no exposure to a particular chemical then there will be no risk at all, for example potassium cyanide in a sealed container is a hazard but not a risk. Risk can therefore be minimized if exposure is minimized. If the chemical is effectively non-hazardous, that is the amount needed to cause harm is unrealistically high, such as with common salt or saccharin, then even if there is a level of exposure, the risk will be so small as to be virtually non-existent. Therefore both the level of exposure and the nature of the chemical (whether or not it is hazardous) must be known if the risk is to be assessed. 

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