Hazard Analysis

Hazard analysis is a critical component of planning for hazardous material releases. It is identification of undesired events that may lead to the realization of the hazard; the analysis of the mechanism by which those undesired events could occur and the estimation of the extent, magnitude & relative likelihood of any harmful effects.

To analyze the safety of a major hazard installation as well as its potential hazards, a hazard analysis should be carried out covering the following areas :

Which toxic, reactive, explosive or flammable substances in the installation constitute a major hazard;

Which failures or errors could cause abnormal conditions leading to a major accident;

The consequences of a major accident for the workers, people living or working outside the installation, or the environment;

Prevention measures for accidents;

Mitigation of the consequences of an accident.

As a first step in hazard analysis, a PHA should be carried out.

A PHA should be used to identify types of potential accident in the installation, such as toxic release, fire, explosion or release of flammable material, and to check the fundamental elements of the safety system.

The PHA should be summarized in documentation covering, for each accident considered, the relevant component (storage vessel, reaction vessel, etc.) the events initiating the accident and the corresponding safety devices (safety valves, pressure gauges, temperature gauges, etc.).

The results of a PHA should indicates which units or procedures within the installation require further and more detailed examination and which are less significance from a major hazard point of view.

A HAZOP is a technique commonly used by chemical process facilities to identify hazards and difficulties that prevent efficient operation. There are two versions of the technique, one which deals with"deviations" and the other with"disturbances"."Deviations" are caused by malfunction or mal operation of a specific production system."Disturbances" include problems caused by influences outside the specified system, including other activities and the environment.

The first version of HAZOP to be developed and the most widely known was aimed at deviations and is called a"Guide word" HAZOP. Each element of the process is evaluated separately. The purpose of the element is specified and notational deviations are generated by associating this purpose of the element with distinctive words or phrases called" guide words". These guide words are"no" or"not","more","less","as well as","part of","reverse", and"other than" which, broadly speaking, cover all possible types of deviation.

For each notational deviation, a determination must be made whether this is a possible situation (e.g., no flow or reverse flow in a transfer line that should have forward flow). If this is possible, the conditions in which that situation might occur and the possible hazardous consequences must be identified. The guide words are applied to all materials and all operating parameters (e.g., flow, temperature, pressure). The guide words are applied not only to the equipment but also to the operating procedures. All phases of operation (e.g. start up, operation, shut down, backwash) must also be included. As would be expected, this approach can be time-consuming and the time taken can vary from several days for a small production unit, to several months for a complex facility.