Process hazard review HAZOP

During process hazards reviews (such as HAZOP), inherent safety concepts are also considered. Mistake proofing the design should receive attention and each safety critical device (last line of defense) and safety critical procedure should be examined to see if there is a way to eliminate the need for the device or procedure. 

Process Hazard Reviews—The facility and subsequent changes are subjected to a process hazard analysis commensurate to the level of hazards the facility represents (i.e.. Checklist, What-If, PHA, HAZOP, Event Tree, FMEA, LOPA, etc.). The results of these analyses are fully understood and acknowledged by management. Where high risk events are identified as probable, quantifiable risk estimation and effects of mitigation measures should be undertaken and applied if productive. 

The second method uses formal Process Hazards Review (PHR) methods such as HAZOP, fault trees, event trees, etc. This approach is utilized most often for ... 

Designs should be based on knowledge of what the human body (and human nature) will do. Include educated operators in design reviews. The HAZOP methodology for process hazard analysis offers an excellent opportunity to identify design and procedural opportunities for inherently safer systems. After all, the OP in HAZOP stands for operability (COPS, 1992). For example, a safe start-up procedure that requires the operator to walk up and down the stairs three times to manipulate valves in the correct sequence can be made inherently safer by locating the valves so that operator has to walk up the stairs only once during the start-up. 

A number of hazard identification and analysis techniques (e.g., HAZOP), can be applied to identify, analyze, and reduce and/or mitigate the process hazards, which includes handling of reactive chemicals and energetic reactions. Chapter 4 provides an overview of these kinds of techniques as related to reactive chemicals mote detailed reviews of hazards analysis techniques are included in [2,3]. 

Hazard and Operability Analysis (Hazop) (Kletz, 1992) is one of the most used safety analysis methods in the process industry. It is one of the simplest approaches to hazard identification. Hazop involves a vessel to vessel and a pipe to pipe review of a plant. For each vessel and pipe the possible disturbances and their potential consequences are identified. Hazop is based on guide words such as no, more, less, reverse, other than, which should be asked for every pipe and vessel (Table 1). The intention of the quide words is to stimulate the imagination, and the method relies very much on the expertise of the persons performing the analysis. The idea behind the questions is that any disturbance in a chemical plant can be described in terms of physical state variables. Hazop can be used in different stages of process design but in restricted mode. A complete Hazop study requires final process plannings with flow sheets and PID s. 

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. 

Several qualitative approaches can be used to identify hazardous reaction scenarios, including process hazard analysis, checklists, chemical interaction matrices, and an experience-based review. CCPS (1995a p. 176) describes nine hazard evaluation procedures that can be used to identify hazardous reaction scenarios-checklists, Dow fire and explosion indices, preliminary hazard analysis, what-if analysis, failure modes and effects analysis (FMEA), HAZOP study, fault tree analysis, human error analysis, and quantitative risk analysis. 

Identification can be as simple as asking what-iP questions at design reviews. It can also involve the use of a checklist outlining the normal process hazards associated with a specific piece of equipment. The major weakness of the latter approach is that items not on the checklist can easily be overlooked. The more formalized hazard-assessment techniques include, but are not limited to, hazard and operability study (HAZOP), fault-tree analysis (FTA), failure mode-and-effect analysis (FMEA), safety indexes, and safety audits. 

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. 

The reader is reminded that a HAZOP or What-If report is a living document for a facility. As changes are made to a facility or its procedures the HAZOP or What-If review(s) will be updated to represent the current facility. Process hazard analysis reviews are also required to be updated and revalidated every five years as a minimum by U.S. regulations (OSHA and EPA). 

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 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. 

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 worksheet (data base spreadsheet) form is used to collect and collate the process hazard analysis review data. A computer software generated spreadsheet is typically used. For a complete description of commercially available HAZOP or What-If software, the user should refer to the manufacturer s HAZOP or What- If software User Instructions. Although pre-printed forms may be used, they are highly inefficient and should be maintained only as a backup in case of computer hardware or software failures. 

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. 

There should be no need for a process hazards analysis during Phase IV— all design decisions should have been pretty much finalized. A final HAZOP smdy and/or checklist review may be needed to close any outstanding issues and to make sure that late changes have been properly analyzed. 

First, the importance of learning lessons from past process safety incidents is highlighted in Section 3.2. The subsequent section presents preliminary hazard review procedure, risk matrix, what-if method, plot plan and layout review, pressure relief system review and fire safety design aspects. Section 3.4 presents PHA techniques and procedures hazards and operability analysis (HAZOP), failure modes and effects analysis (FMEA), instrumented protective system (IPS) design, fault trees, event trees, layer of protection analysis (LOPA) and finally SIS life eyele. The importanee of revision of PSI is highlighted in Seetion 3.5. 

Process Plant Hazard Review using HAZOP... 

A sample HAZOP worksheet for the feed preheater process (Figure 3.7) is presented in Table 3.6 this is for a specific deviation in node 3 of Figure 3.7. The hazard review leader should ensure that basic information such as session date, skid name, node number. 

As identified in a safety review (e.g., process hazard analysis [PHA], What-lf Analysis, Hazard and Operability Study [HAZOP]), a defined part (section or subsystem or item of equipment) of a process that has a design intention that is specific and distinct from the design intention of other process parts, which allows the study team to analyze the specific equipment or system in an organized fashion. 

To develop the risk-management strategy, start with a process hazards analysis (PHA) and review the process design and its control, operation, and maintenance practices. Select a multidisciplinary team with expertise in these areas, and use an accepted hazard-evaluation procedure, such as a hazard and operability (HAZOP), what-if, or checklist analysis, to determine how process deviations from intended... 

Have the recommendations from safety reviews. Process Hazards Analysis (PHA), Hazards and Operability Reviews (HAZOP), CHAZOP, or others, been implemented Record any incomplete items. ... 

---