Alternate release scenario

Hazard assessment. A hazard assessment is required to assess the potential effects of an accidental (or intentional) release of a covered chemical/material. This RMP element generally includes performing an off-site consequence analysis (OCA) and the compilation of a five-year accident history. The OCA must include analysis of a least one worst-case scenario. It must also include one alternative release scenario for the flammables class as a whole also each covered toxic substance must have an alternative release scenario. USEPA has summarized some simplified consequence modeling... 

Estimating distances. For both the worst-case and alternative release scenarios, the source must estimate the distance to where the endpoint is no longer exceeded and estimate the population (rounded to two significant digits) within a circle defined by the distance and centered at the release point. U.S. Census data may be used and it does not have to be updated however, the presence of sensitive populations (e.g. hospitals, schools, etc.) must be noted. In addition, the source must identify and list the types of environmental receptors within the calculated worst-case distance and circle however,... 

Consequence Analysis X X X Applies to all. Alternate release scenario does not apply to Level 1. 

The offsite consequence analysis requires that the facility determine (1) the worst-case consequence distance, where all of the chemical is released under an F atmospheric stability condition and a wind speed of 1.5 m/s (meters per second) and (2) alternative release scenarios. This is done for each chemical. The worst-case and alternative release scenarios require that the toxic plume from the hypothetical spill be modeled to a toxic endpoint (in mg/m ) and the downwind distance to that endpoint be determined. The facility must also identify offsite receptors within the circle defined by the worst case and alternative release scenarios. Offsite receptors include public receptors (list population within circle, identify schools, commercial or industrial areas, etc.) and environmental receptors (wUdUfe sanctuaries, preserves, national forests, state parks, etc.). The facility does not need to consider the consequence of a toxic plume on the offsite receptors, only identify them. 

The alternative release scenario could include a worst-case release amount but with passive (e.g., dikes or sumps) or active responses (e.g., a deluge system, emergency shutdown system) in place, or a release based on past history. The modeling is done under either typical meteorological conditions or a D atmospheric stability and a wind speed of 3 m/s. 

Alternative release scenario. Alternative release scenarios must be more likely to occur than the worst-case scenario, and must reach an off-site endpoint. The EPA says owners should also consider these factors in selecting alternative release scenarios five-year accident history and failure scenarios identified by a process hazard analysis (PHA) or Program Level 2 hazard review. The alternative release scenario analyses may be performed using somewhat more flexible modeling approaches and parameters than specified for worst-case scenario analyses. For example, active mitigation credit can be given. 

An off-site consequence analysis that evaluates specific potential release scenarios, including worst-case and alternative scenarios... 

Alternative release cases for toxic substances cover scenarios with toxic concentrations beyond the fenceline. Alternative cases for flammable substances cover scenarios that may cause substantial damage off site and on site. The release scenarios that have a potential to reach the public are of the greatest concern. Those with no off-site potential damage are not required to be reported. 

As an alternative to these calculations, the registrant may choose to make a generic release estimate. Here, conservative default values are used for identifying waste amounts and fractions entering into the three main waste streams. Furthermore, generic exposure scenarios can be selected containing default release factors and assumptions on implemented risk management in the processes. [19]. 

Additional tests such as the addition of nucleophilic scavengers (e.g., thiols such as dithiothreitol or j8-mercaptoethanol) can provide further evidence for the presence of a free, reactive electrophilic species. The scavengers should quench all of the free reactive species, thereby protecting the enzyme from inhibition. Unfortunately, this method cannot exclude the possibility that a nucleophilic thiol may even attack the bound reactive species at the active site of the enzyme (which would also give rise to protection from inactivation). However, the use of a bulky thiol, such as reduced glutathione, should limit that possibility. An alternative scenario occurs wherein the released reactive species returns and reacts faster with an active-site nucleophile than with the added thiol. Clearly this is a complex problem and, consequently,it is advisable to use several different tests to avoid misleading conclusions. 

If either of these situations could exist, the EPA standard recommends that the consequences of a flash fire be evaluated as an alternative scenario for a flammable-liquid release and be described in terms similar to those listed under Toxicity Hazards. 

The EPA standard does not require an off-site consequence analysis for pool fires unless the thermal-radiation endpoint (5 kilowatts/m ) is outside the property boundary, or unless there are locations within the property boundary to which the public has routine and unrestricted access during or outside business hours. If either of these situations could exist, the EPA standard recommends that the consequences of a pool fire be evaluated as an alternative scenario for a flammable-liquid release and be described in terms similar to those listed under Toxicity Hazards. 

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