Consequence Analysis

Consequence analysis process safety


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Risk has four elements:

  1. A hazard;
  2. The consequences of that hazard should it occur (safety, environmental and economic);
  3. The likelihood of occurrence of the hazard; and
  4. Safeguards that reduce consequences and/or likelihood.

The relationship between the first of the above three terms is shown in the following Equation.

RiskHazard  =  Consequence  *  Predicted Frequency 

This ebook discusses the consequence term, including fires, explosions and toxic gas releases.

The topics of consequence and likelihood analysis are fraught with issues that bring into question the accuracy and usefulness of the results because so many assumptions have to be made, and because the analysts’ opinions (many of which are implicit) play such an important role. For example, many fires and toxic gas releases start with a leak from a piping system. Yet the size of the leak could vary from a pinhole, to a partially failed gasket all the way to a complete guillotine break of the pipe. Clearly the assumption made about leak size is going to strongly affect all discussions to do with the consequences and likelihood of that leak.

The subjectivity that is implicit in analysts’ opinions is very difficult to recognize. For example it is likely that anyone who has suffered from H2S exposure would treat a release of that gas as being very significant, regardless of what the calculations say. Similarly, people will often give a higher probability of occurrence to events that have already occurred once than to events that have never occurred.

Table of Contents

Range of Consequences 
   Effect of a Release 
Hole Size 
   Flammable Range 
   Ignition Temperature / Energy 
   Spontaneous Combustion 
   Ignition Sources 
      Vacuum Trucks 
      Radiant Heat
      Static Electricity 
      Pyrophorics / Iron Sulfide 
   Flammability Hazard Ranking
   Passive Fire Protection / Fireproofing
   Physical Explosions 
   Vapor Cloud Explosions 
   Deflagrations and Detonations
   Blast Effects
   Dust Explosions
Toxic Gas Releases
   Gas Release Modeling 
   Effect of Toxic Gases
   Probit Equations
   Short-Term Exposure Limits
      Emergency Response Planning Guidelines (ERPGs)
      Immediately Dangerous to Life and Health
      Permissible Exposure Limits (PEL) 
      Threshold Limit Values (TLV)
      Short Term Exposure Limit (STEL)
      Levels of Concern (EPA)
      Acutely Toxic Concentration / Levels (New Jersey / Delaware)
      Substance Hazards Index
   Location of Monitors 

Process safety consequence analysis