WHAT ARE HAZARDS ? HAZARD ANALYSIS , HAZOP STUDY & HAZOP PROCEDURE

HAZARDS

Hazards are everywhere, Unfortunately a hazard is not always identified until an accident occurs. It is essential to identify the hazards and reduce the risk well in advance  of an accident.

For each process in a chemical plant  the following questions must be asked.

     1.    WHAT ARE THE HAZARDS ?

     2.    WHAT CAN GO WRONG AND HOW ?

     3.    WHAT ARE THE CHANCES ?

     4.    WHAT ARE THE CONSEQUENCES ?

The first question represents hazard identification. The last 3 questions are associated with risk assessment. Risk assessment includes a determination of the events that  can produce an accident  , the probability of those events , and the consequences . The consequences could include human injury or loss of life, damage to the environment or loss of production or damage to the equipment which ultimately leads to loss of huge capital investment.

HAZARD ANALYSIS

Hazard Analysis is nothing but the risk assessment. A risk assessment procedure that determines probabilities is frequently called Probabilistic Risk Assessment(PRA), whereas a procedure that determines probabilities and consequences is called Quantitative Risk Analysis(QRA). Hazard Analysis can be performed at any stage during the initial design or ongoing operation of a process.

HAZOP STUDY

The HAZOP study is a formal procedure to identify hazards in a chemical process facility. The procedure is effective in identifying hazards and is well accepted by the chemical industry.

The basic idea is to let the mind go free in a controlled fashion in order to consider all the possible ways that process and operational failures can occur.

Before the HAZOP study is started detailed information on the process must be available. This include up-to-date PROCESS FLOW DIAGRAM (PFD), PROCESS AND INSTRUMENTATION DIAGRAM (P&ID), detailed equipment specifications, material of construction, and mass and energy balances.

A large process might take several months of biweekly meetings to complete the HAZOP study. Obviously, a complete HAZOP study requires a large investment in time and effort, but the value of the result is well worth the effort.

The HAZOP procedure uses the following steps to complete an analysis :

1.    Begin with a detailed flowsheet. 

2.  Break the flowsheet into a number of process units (means the reactor area might be one unit and the storage tank another). 

3.    Select a unit for study. 

4.    Choose a study node (vessel, line, operating instructions). 

5.    Describe the design intent of the study node (for example, a vessel V-1 is designed to store the benzene feedstock and provide it on the demand to the reactor). 

6. Pick a process parameter (flow, level, temperature, pressure, concentration, etc). 

7. Apply a guide word to the process parameter to suggest possible deviations (for example, NO, HIGHER, LOWER, WHERE ELSE, OTHER THAN, SOONER THAN, LATER THAN, etc). 

8. If the deviation is applicable , determine possible causes and note any protective systems. 

9.    Evaluate the consequences of the deviation. 

10.  Recommend action. 

11.   Record all the information. 

12. Repeat steps 7 to 11 untill all the applicable guide words have been applied to the choosen parameter. 

13. Repeat steps 6 to 12 untill all the applicable process parameter has been considered. 

14.  Repeat steps 4 to 13 untill all the study nodes have been considered.