Process hazard/operability study

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. 

PHA (Process Hazard Analysis) Study PHA study during FEED stage is crucial as it may require changing some or a major part of the project due to process safety risks. It has potential to escalate the project cost significantly. PHA study is conducted by the PHA leader, who is a highly qualified process/safety engineer with many years of operations and... 

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

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

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. ... 

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. 

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. 

The incidents described could occur in many different types of plants and are therefore of widespread interest. Some of them illustrate the hazards involved in activities such as preparing equipment for maintenance and modifying plants. Others illustrate the hazards associated with widely used equipment, such as storage tanks and hoses, and with that universal component of all plants and processes people. Other incidents illustrate the need for techniques, such as hazard and operability studies, and protective devices, such as emergency isolation valves. 

All of these factors determine the stress experienced by the workers and the extent to which operational errors will be recovered before disastrous consequences have ensued. In this context, hazard identification techniques, such as hazard and operability studies (HAZOP), failure modes and effects and criticality analysis (FMECA), fault trees, and others are useful in making the process environment more forgiving. 

What if Approaches Hazind and Operability (HAZOP) Studies Preliminary Hazard Analysis (PLHA) Process Hazard Analysis (PHA)... 

Hazard or event identification provides information on situations or chemicals and their releases tliat can potentially hanii tlie emaromiient, life, or property. Inforniation that is required to identify hazards includes chemical identities, quantilics and location of chemicals in question, chemical properties such as boiling points, ignition temperatures, and to.xicily to hmnans. There arc sci cral nictliods used to identify hazards. The methods that will be discussed later in tliis Part w ill include tlie process checklist and tlie hazard mid operability study (HA20P). 

Hazard identification provides information on situations or chemicals tliat can potentially liann tlie environment, life, or property. Tlie processes described are process checklist, event tree, hazard and operability study. 

A three-step nitration process of toluene is described. The advantages of the modified process are reduced waste, less hazardous operation, reduced oleum requirement, partial replacement of coned HN03 with dil HN03, and higher rate of toluene flow into the reactor (Ref 86) The continuous process of H.C. Prime (Ref 73) for preparing TNT was studied by thin-layer chromatography on silica gel with a starch binder and a fluorescent indicator. The nitration... 

New systems or processes may also need to be qualified from an operational safety perspective. This is particularly relevant in the case of chemical synthesis involving exothermic reactions. Critical safety aspects are usually identified using hazard operability or HAZOP assessments and studies. For example, a HAZOP analysis of an exothermic reaction vessel would involve consideration of the consequence of failure of the motors for mixers or circulation pumps for cooling water. Thus, the qualification of such a system would involve checks and assessment to ensure that the system/process can be operated safely and that pressure relief valves or other emergency measures are adequate and functional. 

A HAZOP (Hazard and Operability Study) involves a formal review of process and instrumentation diagrams by a specialist team using a structured technique, based upon key words. These comprise property words and guide words , e.g. as in Table 12.4. 

A hazard and operability study is a procedure for the systematic, critical, examination of the operability of a process. When applied to a process design or an operating plant, it indicates potential hazards that may arise from deviations from the intended design conditions. 

When using the operability study technique to vet a process design, the action to be taken to deal with a potential hazard will often be modifications to the control systems and instrumentation the inclusion of additional alarms, trips, or interlocks. If major hazards... 

As the flowsheet becomes more firmly defined, the detailed process and mechanical design of the equipment can progress. The control scheme must be added and detailed hazard and operability studies carried out. All this is beyond the scope of the present text. However, all these considerations might require the flowsheet to be readdressed if problems are uncovered. 

The what-if analysis is a creative, brainstorming examination of a process or operation conducted by a group of experienced individuals able to ask questions or voice concerns about undesired events. It is not as inherently structured as some other methods, such as the hazard and operability (HAZOP) study or a failure mode and effects analysis (FMEA). 

V Process hazard analysis (PHA) must be performed by a team of experts, including engineers, chemists, operators, industrial hygienists, and other appropriate and experienced specialists. The PHA needs to include a method that fits the complexity of the process, a hazards and operability (HAZOP) study for a complex process, and for less complex processes a less rigorous process, such as what-if scenarios, checklists, failure mode and effects analysis, or fault trees. 

Hazards identification and risk assessment studies can be performed at any stage during the initial design or ongoing operation of a process. If the study is performed with the initial design, it should be done as soon as possible. This enables modifications to be easily incorporated into the final design. 

---