User:Milton Beychok/Sandbox

A Hazard and Operability Study (HAZOP) is a simple, structured methodology for identifying, evaluating and prioritizing potential hazardous occurrences in an existing process facility or a proposed new facility. The HAZOP methodology is a safety analysis that uses and encourages imaginative thinking (or brainstorming) and was first developed by Imperial Chemical Industries (ICI), a British chemical company. It is performed by a multi-disciplinary HAZOP team and entails the use of guide words to stimulate the brainstorming. For a proposed new process facility (such as a petroleum refinery, natural gas processing plant or chemical plant), a HAZOP may require many weeks to perform.

Although the HAZOP methodology was originally developed to study chemical process facilities, it has been extended to other types of facilities and complex operations.

There are many other hazard evaluation (HE) techniques, some of which are simpler than a HAZOP and some of which are more complex. For example, the Checklist and What-If methodologies are simpler than a HAZOP, and the Failure Mode Effects and Analysis (FMEA) and Fault Tree methodologies are more complex. In the United States as well as some other nations, governmental regulations require some type of hazard evaluation be performed for certain, specified types of existing or proposed new process facilities.

What a HAZOP is not

A HAZOP is not an method to determine how far one can go in physically removing or mitigating all risks nor is it a method for defining engineering or procedural solutions for eliminating sources of risk.

Most importantly, it is not a guarantee that adverse consequences will not occur.

Terminology

Table 1 provides a list of the terms pertinent to a HAZOP along with their definitions:

Table 1: Terminology and Definitions

Term	Definition
Hazard	A source, situation, event, circumstance or condition with the potential to cause harm, including ill health, injury or death, production losses, or damage to the environment.
Study nodes (or process sections)	Section of the process equipment with definite boundaries (for example, the piping from a process vessel to a pump) within which process parameters are investigated to determine the effect of deviations from the design intention and the potential of a hazard being created in that section.
Process parameter	A physical or chemical property involved in a study node, including items such as temperature, pressure, pH, concentration, reaction or volume.
Deviation	Departures from the design intention that are discovered by systematically applying the pertinent guide words applicable for each study node.
Design intention	Definition of how the study node is expected to operate in the absence of deviations from the process design.
Guide words (or guidewords)	Simple words used to qualify the the design intention and to guide and stimulate the brainstorming process for identifying potential process hazards.
Safeguards (or protection systems)	Administrative controls (such as operating manuals and work procedures) or engineered systems designed to prevent deviations or to mitigate the consequences of deviations.

Matrix of guide words and process parameters

Table 2 presents an example matrix of which typical guide words are applicable to each of a typical set of process parameters:

Table 2: Example Matrix of Guide Words and Process Parameters

Guide word $\Rightarrow$ Parameter $\Downarrow$	More	Less	None	Reverse	Part of	As well as	Other than
Flow	x	x	x	x	x	x	x
Temperature	x	x
Pressure	x	x	x	x
Level	x	x	x
Volume	x	x	x		x
Mixing	x	x	x
Composition							x
Reaction	x	x	x	x			x
pH	x	x
The letter x denotes which guide words are applicable to each of the process parameters.

As noted, the above Table 1 is merely a typical example. The HAZOP team will select the appropriate sets of guide words and process parameter that are to be used for the process or operation being studied.

The HAZOP team

The team that will perform the HAZOP should consist of personnel with a good understanding of the process facility to be studied.The team members should be people from a range of disciplines and that is one of the strengths of the HAZOP methodology.

A HAZOP team typically meets daily for sessions of 3 to 6 hours each and, as noted above, it may require many weeks to perform the HAZOP. A typical team should be limited to no more than about 8 to 9 members and include:

A team leader: It is important that the team leader be someone from outside the immediate organization of the facility being analyzed and, ideally, come from a completely independent company. The leader should be experienced in the HAZOP methodology and have in-depth knowledge of how chemical process facilities work even though he or she may not have an intimate knowledge of the technology involved in the particular facility being studied.

A scribe or recorder: The primary function of the scribe is to record and and document the proceeding of the HAZOP sessions as well as any recommendations made by the team.

Process designer(s): One or more representative(s) of the team that designed the facility to explain the process design and provide other information that may be needed. If the process design of the facility involved an outside contractor or process licensor, then they should provide a knowledgeable process design representative.

Facility operator: A representative of the workers selected to operate the facility.

Process control expert: A process control expert to provide expertise on the instruments and control systems, as well as the safety shutdown systems. He or she should be a full-time member of the team.

Maintenance representative: If appropriate, the team should include a representative of the facility's maintenance department.

Specialist(s): At times, specialists may be needed for limited time periods. For example, if the team is studying some issues involving corrosion, it may need the help of a corrosion expert for that part of the HAZOP.

Pre-HAZOP preparations

Before the HAZOP commences, the team leader should:

• Identify and locate up-to-date process flow diagrams (PFDs), piping and instrumentation diagrams (P&IDs), a facility site layout (plot plan) and all equipment design specifications and construction drawings. Also, locate the startup, operating and shut-down manuals and procedures.

• Participate in selecting the appropriate team members, orient them as to the HAZOP methodology and provide some basic training in HAZOPs if needed.

• Prepare a schedule for the HAZOP session meetings and distribute it to the team members.

• Develop a list of the guide words to be used for the HAZOP and make sure that the team members agree with the list.

Methodology

(PD) Diagram: Milton Beychok
Figure 1: The sequence of steps in performing a HAZOP

Risk Ranking

Risk Ranking Matrix

Severity	Liklihood
	Frequent	Probable	Occasional	Remote
Major	Unacceptable	Unacceptable	Unacceptable	High
Moderate	Unacceptable	High	High	Medium
Small	High	Medium	Low	Low
Insignificant	Medium	Low	Low	low
Frequent = Once or more per year Probable = Between once or more per year and once per 10 years Occasional = Between once per 10 years and once per 30 years Remote = less than once per 30 years