Hazard Operability Study

Recognized systematic approaches include hazard operability study (HAZOP) event tree analysis fault tree analysis. 

Once a complete flowsheet has been developed, the operability and control of the process can be considered. Moreover, the economic incentive for modifying the flowsheet to improve the control can be considered. Then a (hierarchical) procedure for the synthesis of a control system for the complete plant can be used as an additional tool for screening the process alternatives, and a preliminary hazardous operations study can be initiated. The results of this conceptual design study then provides an estimate of the economic incentive for initiating a more rigorous design study. 

Hazard operability study—A structured means of evaluating a complex process to find problems associated with operability or safety of the process. 

The timing of accidents can be determined through a severe accident progression analysis. This can be done using a probabilistic safety analysis level 1, through the use of failure mode and effects analysis (FMEA) techniques, or hazard operability studies (HAZOPs). The important parameters are toe time between the recognition of an accident by the operator (i.e., the declaration of an emergency) and the onset of the release, the release rate, and the duration of the release. 

Brainstorming, questionnaires, business process studies, industry benchmarking, scenario analysis, risk assessment workshops, incident investigation, auditing, and inspection, HAZOP (HAZard OPerability Studies)... 

M. Rausand, HAZOP Hazard Operability Study, Norwegian University of Science and Technology, October 2005. 

Use of Hazard Operability Studies in Process Risk Management... 

Hazard identification a process to identify hazards and associated risk to persons, property, and structures and to improve protection from natural and human-caused hazards Hazard Identification and Risk Assessment (HIRA) a process to identify hazards and associated risk to persons, property, and structures and to improve protection from natural and human-caused hazards HIRA serves as a foundation for planning, resource management, capability development, public education, and training and exercises Hazard operability study a structured means of evaluating a complex process to find problems associated with operability or safety of the process Hazard rating (NFPA) classification system that uses a four-color diamond to communicate health, flammability, reactivity, and speciflc hazard information for a chemical substance a numbering system that rates hazards from zero (lowest) to four (highest)... 

Here we shall restrict consideration to safety and health considerations that can be built in while the design is developing rather than the detailed hazard and operability studies that take place in the later stages of design. The three major hazards in process plants are fire, explosion, and toxic release. ... 

As the design progresses, it is necessary to carry out hazard and operability studies. These are generally only meaningful when the design has been progressed as far as the preparation of detailed flowsheets and are outside the scope of this text. 

Design procedures are developed with the intention of improving the safety of equipment. Tools used in this step are hazard and operability studies and quantitative risk analysis (ORA). The following scheme may be used ... 

Control of Plant and Process Modifications Many accidents have occurred because plant or process modifications had unforeseen and unsafe side effects (Sanders, Management of Change in Chemical Plants Learning from Ca.se Histories, Butterworth-Heinemann, 1993). No such modifications shoiild therefore be made until they have been authorized by a professionally quahfied person who has made a systematic attempt to identify and assess the consequences of the proposal, by hazard and operability study or a similar technique. When the modification is complete, the person who authorized it... 

HAZOP (Knowlton, 1989 Lees, 1980 CPQRA, 1989, pp. 419-422). HAZOP stands for hazard and operability studies. This is a set of formal hazard identification and elimination procedures designed to identify hazards to people, process plants, and the environment. The techniques aim to stimulate in a systematic way the imagination of designers and people who operate plants or eqmpment so they can identify potenti hazards. In effect, HAZOP studies make the assumption that a hazard or operating problem can arise when there is a deviation from the design or operating intention. Corrective actions can then be made before a real accident occurs. 

Hazard and Operability Study (HAZOP) A systematic qualitative technique to identify process hazards and potential operating problems using a series of guide words to study process deviations. 

R. E. Knowlton, Hazard and Operability Studies, The Guide Word Approach, Chemetics International Company, Vancouver, BC, 1981. 

A HAZOP (Hazard and Operability Study) involves a fonual review of proeess and instrumentation diagrams by a speeialist team using a stmetured teehnique, based upon key words. These eomprise property words and guide words , e.g. as in Table 12.4. 

Hazard and operability study prior to implementation (repeat when in use) Updating of all operating instructions, notices, procedures Removal/isolation of obsolete plant/lines Control of changes in personnel (see training)... 

Refresher course on fundamentals of safety, hazard recognition, procedures Participation in hazard and operability studies on existing operations and procedures... 

A pesticide manufacturing plant should prepare a hazard assessment and operability study and also prepare and implement an emergency preparedness and response plan that takes into account neighboring land use and the potential consequences of an emergency. Measures to avoid the release of harmful substances should be incorporated in the design, operation, maintenance, and management of the plant. Implementation of cleaner production processes and pollution prevention measures can yield both economic and environmental benefits. 

Many accidents occur because process materials flow in the wrong direction. Eor example, ethylene oxide and ammonia were reacted to make ethanolamine. Some ammonia flowed from the reactor in the opposite direction, along the ethylene oxide transfer line into the ethylene oxide tank, past several non-return valves and a positive displacement pump. It got past the pump through the relief valve, which discharged into the pump suction line. The ammonia reacted with 30m of ethylene oxide in the tank, which ruptured violently. The released ethylene oxide vapor exploded causing damage and destruction over a wide area [5]. A hazard and operability study might have disclosed the fact that reverse flow could occur. 

We put a lot of effort into improving safety by adding protective equipment onto our plants, new and old gas detectors, emergency isolation valves, interlocks, steam curtains, fire insulation, catchment pits for LPG storage tanks, and so on. We also introduced new procedures, such as hazard and operability studies and modification control, or persuaded people to follow old ones, such as permits-to-work and audits. 

This incident shows the importance, during hazard and operability studies (see Chapter 18), of considering abnormal conditions, such as failure of utilities, as well as normal operation. 

Should the design team have foreseen that the condensate might freeze A hazard and operability study (see Chapter 18) would probably have drawn attention to the hazard. 

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