HAZOP review

Technical and trade organi2ations are concerned with safety and the environment. The Chlorine Institute in North America and Euro Chlor in Western Europe are examples of organi2ations dedicated to the safe production, transport, and use of chlorine. Ha2ard and operabiHty studies (HAZOP) reviews for new designs, plants, and expansions (135) have become required by poHcy in many operating companies. Papers on safety and environmental subjects are given at most technical meetings (136—138). 

The following event scenarios of concern were identified during a thorough HAZOP review that was performed as part of this assessment ... 

HAZOP Review of the Chlorine Railcar Unloading System 4 CHLORINE VAPORIZER... 

HAZOP reviews follow a definitive guideword approach, step by step. A What-If analysis is usually combined with a checklist in the petrochemical industry to provide a "road map" for the review. 

HAZOP reviews have been stated as arising from the chemical industry in Britain during the 1960 s. Imperial Chemical Industries, Ltd. (ICI) developed a standardized method of analyzing processing hazards based on the basic operation conditions and then changed individual parameters one at a time to see the subsequent consequences. This evolved into a standard practice within their company and soon found its way into the general chemical industry (although it was not universally or consistently applied). 

The review is a thorough and systematic process which has to be conducted in a proper fashion and accurately recorded. In order to perform a HAZOP review a specialized team leader is typically used to guide the review team during the process. The team leader usually has had specialized training and experience in the conduction of HAZOP reviews. 

If a final HAZOP review is to be performed on a design that is say only 75% complete, the review team will necessarily have a lot to say about the unfinished portion of the design. The scheduled review method should be consistent with the level of design that will be presented for review. 

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. 

Both HAZOP or What-If reviews are generally organized and conducted in a similar fashion. The HAZOP review is more detailed and structured, while the What-If approach is typically broader and free flowing. 

It has been found that the What-If style of process hazard analysis is a convenient method to use for a "simple" facility. For simple facilities, the detailed HAZOP approach has been found to be tedious and just as productive as a What-If method. The What-If approach stimulates generation of new ideas and discussion to cover issues associated with the items under review, as well as addressing generic issues. The specific HAZOP review is not necessary when the process is simple and well understood by the reviewing team. The team can readily review the major items of concern by asking What-If questions such as what happens when a pump fails, without relying on itemized and detailed variations of a process condition by the HAZOP method, such as high level, low pressure, etc. 

A HAZOP review method is suggested for the process when the following more complex facilities are under study. These facilities contain processes which typically are complex in nature, have chemical processes containing volatile hydrocarbons/toxic chemicals, or have high employee concentrations ... 

Global deviations should sometimes be considered in a HAZOP review. Global deviations are generally considered the effects that would simultaneously effect the entire process or facility. These are, but not limited to, equipment layout, seismic activity, flooding, sandstorm, extreme weather conditions, loss of power, human factors, etc. 

Typically it takes an experienced team about two hours to thoroughly complete a single node for a HAZOP review and one hour for a What-If review. A P ID sheet with two nodes is estimated to require four hours to review for a HAZOP and two hours for a What-If approach. It can readily be seen that a What-If review typically requires one half the time to accomplish that of a HAZOP. A formula to estimate the manhours to accomplish a review has been formulated based on historical observations. Manhours expended to accomplish a review can be easily estimated by multiplying the estimate for... 

The following are typical guideword parameter, deviations, and possible causes that are used in HAZOP reviews. This listing is by no means exhaustive and each review should be supplemented or tailored to meet the needs of a particular facility. 

The purpose of a HAZOP review is to identify hazards before an incident - not necessarily to solve how to eliminate or minimize the potential hazard. Some solutions are obvious and can be handled immediately. However, many solutions may be complex and should be assigned to others to solve outside of the HAZOP review process. 

Even if you never participate in a formal HAZOP review, the principles are extremely valuable in everyday operations as it broadens thinking to include more potential problems and to handle them in a systematic way. 

Fault tree analysis is many times requested because of complex hazards identified by a HAZOP review. Engineering has some people trained in analytical tree development and analysis and they are responsible for conducting these type studies. 

Order of Addition—Variation in the order of addition of substrate, alkylUthinm, and electrophile are possible. The method of choice will be dictated by the chemistry. Inverse addition of the substrate to a solution of -BuLi in the appropriate solvent may be a particularly useful approach, because it ensures that there is an excess of the alkyllithium at all times during the addition. Clearly, potential problems (HAZOP review) that may result from starting with a reactor charged with n-BuLi need to be considered. 

The HAZOP reviews will look at each detail of the process, examine what is happening in that stage of the process, and then question a series of what if potential failures. Questions such as a failure of a control, loss of power, will generate a list of possible reactions to that failure mode. The failure list is then generated from experience with similar process arrangements... 

Acronyms and abbreviations What-if anaiysis worksheets HAZOP review worksheets... 

Once a layout has been approved by all disciplines (including Hazop review where applicable) and frozen, its integrity has to be maintained through the following detail design stages to prevent unauthorized encroachment on discipline space and the compromising of access ways. 

ACRONYMS AND ABBREVIATIONS WHAT-IF ANALYSIS WORKSHEETS HAZOP REVIEW WORKSHEETS... 

PHA, What-If, Bow-Tie, and HAZOP reviews are the most common industry quahtative methods used to conduct process hazard analyses, while SVAs are typically applied for process security analyses requirements. It is quahtatively estimated that up to 80% of a company s hazard identification and process safety analyses may consist of PHA, What-If, Bow-Tie, and HAZOP reviews, with the remaining 20% from Checkhst, Fault Tree Analysis, Event Tree, Failure Mode, and Effects Analysis, etc. 

Running for a long period of time with a control valve bypass open in hydrocarbon service should be considered a change in operation requiring a HAZOP review. For me, as a field troubleshooter. I ll always close all control valve bypasses I opened during my investigations before I leave the plant in the evening. 

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