HAZOP and What-If Analyses

These analytical methodologies were first developed for the petrochemical industry with the intent to reduce the probability and/or consequences of a major incident 

Basic Guide to System Safety, Third Edition. Jeffrey W. Vincoli. 

For the purpose of this text, the following definitions are provided for the HAZOP study and the What-If analysis  

HAZOP A formal, systematic, logical, and stmctured investigative study for examining potential deviations of operations from design conditions that could create process-operating problems and hazards. 

What-If Analysis An informal but somewhat structured investigative method for introducing and evaluating hypothetical events, or series of events, associated with the operation of a given facility or process. 

---

Table 14.1 (Nolan 1994) provides an example listing of some of the more common reference sources typically identified for use in HAZOP and What-If analyses. The challenge is to identify and obtain a//potential source data to ensure a comprehensive...

HAZOP and What-If reviews are two of the most common petrochemical industry qualitative methods used to conduct process hazard analyses. Up to 80% of a company s process hazard analyses may consist of HAZOP and What-If reviews with the remainder 20% from Checklist, Fault Tree Analysis, Event Tree, Failure Mode and Effects Analysis, etc. An experienced review team can use the analysis to generate possible deviations from design, construction, modification, and operating intent that define potential consequences. These consequences can then be prevented or mitigated by the application of the appropriate safeguards. 

In HAZOP studies and what-if analyses, the review team must first identify the areas or components of the system that will each be analyzed during the review process. In the chemical industry, these individual components are typically referred to as nodes. There are three basic criteria for identifying the nodes to be reviewed (Nolan 1994) ... 

Once all what-if analysis questions have been asked and answered along with all completed HAZOP studies of system components, a final report should be written to document all findings and recommendations. In the chemical industry (in the United States), this report is normally referred to as a process hazard analysis. This report is required under both OSHA and EPA regulations for facilities that handle or contain certain chemical commodities at certain defined quantity thresholds. However, when HAZOP studies and what-if analyses are used in general industry application, documentation of the results can be included in a written report along with any other system safety analyses that may have been performed (as described in previous chapters). If the HAZOP and what-if exercises were conducted as standalone analyses, then a final written report should be... 

The cost of performing the hazard identification step depends on the size of the problem and the specific techniques used. Techniques such as brainstorming, what-if analyses, or checklists tend to be less expensive than other more structured methods. Hazard and operability (HAZOP) analyses and failure modes and effects analyses (FMEAs) involve many people and tend to be more expensive. But, you can have greater confidence in the exhaustiveness of HAZOP and FMEA techniques—their rigorous approach helps ensure completeness. However, no technique can guarantee that all hazards or potential accidents have been identified. Figure 8 is an example of the hazards identified in a HAZOP study. Hazard identification can require from 10% to 25% of the total effort in a QRA study. 

Before any mitigation measures can be designed, an effective hazard identification study must be conducted. The results of such a study (a set of release scenarios) can be used to develop a coherent set of mitigation strategies. In the process industries, these studies are most commonly conducted using hazard and operability (HAZOP) studies, what-if checklists, failure modes and effects analyses (FMEA), and several other comparable techniques (CCPS, 1992). 

These reviews can be either in addition to or combined with periodic process hazard analyses (PHAs) by using methods such as what-if analysis and HAZOP studies. The latter should consciously focus on identifying scenarios in which intended reactions could get out of control and unintended reactions could be initiated. One means of accomplishing this as part of a HAZOP study has been to include chemical reaction as one of the parameters to be investigated for each study node. Johnson and Unwin (2003) describe other PHA-related approaches for studying chemical reactivity hazards. 

The facility is subjected to a process hazard analysis commensurate to the level of hazard the facility represents (i.e., Checklist, PHA, HAZOP, What-If review, Event Tree, FMEA, etc.). The results of these analyses are fully understood and acknowledged by facility management. Where high risk events are identified, quantifiable risk estimation and effects of mitigation measures should be evaluated and applied if productive. 

The bulk of process hazard analyses (PHA) in the petroleum and related industries will be either a HAZOP or a What-If review. Generally in the upstream sector, 60 - 80% of the safety reviews will be a What-If review, while in the downstream sector, 60 - 80% will be HAZOP reviews. 

There are various types of analyses that are used for a process hazard analysis (PHA) of the equipment design and test procedures, including the effects of human error. Qualitative methods include checklists, What-If, and Hazard and Operability (HAZOP) studies. Quantitative methods include Event Trees, Fault Trees, and Failure Modes and Effect Analysis (FMEA). All of these methods require rigorous documentation and implementation to ensure that all potential safety problems are identified and the associated recommendations are addressed. The review should also consider what personal protective equipment (PPE) is needed to protect workers from injuries. 

If the other elements of the PSM program have been properly implemented, particularly the MOC and Prestartup Safety Review (PSSR) elements, then the hazards analysis validation should be quite straightforward. If the first hazards analysis was a HAZOP, it is often appropriate for the subsequent analyses to use either the What—If or the Checklist methods. Doing so will save time, and will probably provide for a superior analysis because the team members will be using a fresh way of thinking and will be less likely to be bored. 

The successful use of both the HAZOP study and the What-If analysis is dependent upon the expertise and experience of the individuals that comprise the review teams. Essentially, both are really nothing more than exercises in communication. While each method can be conducted as separate analyses, the What-If analysis is almost always a primary component of a complete HAZOP study. Information is presented, discussed, analyzed, and recorded. Specific safety aspects and requirements are identified so that appropriate design considerations can be determined. The objective is accident prediction and the end result is accident prevention. 

There are many hazard analysis formulations which may be used effectively to assess process hazards. These include fault-free analysis, failure mode and effect analysis (FMEA), what-if analysis, hazard and operability analysis (HAZOP), check list analysis, and safety review, among others. The specifics associated with these analyses can be reviewed by consulting the appropriate American Institute of Chemical Engineers Center for Chemical Process Safety reference. " ... 

As part of Process Safety Management (PSM) requirements by both OSHA and the EPA, both risk analysis and emergency response management require the determination (i.e., identification and evaluation) of incident scenarios that are likely to develop at an installation. Risk analyses techniques such as PITA, What-If, HAZOP, etc., will systematically review a process to determine possible deviations from the intended processes that may result in events such as fire and explosions. Additionally, emergency response preparedness plans usually develop creditable scenarios that may develop and the generic responses that are required. These PSM techniques... 

---