Process Hazard Analysis (PHA) is a set of organized and systematic assessments of the potential hazards associated with industrial processes. A PHA provides information intended to assist in making decisions for improving safety and reducing the consequences of unwanted or unplanned releases of hazardous chemicals. A PHA is directed toward analyzing potential causes and consequences of fires, explosions, releases of toxic or flammable chemicals and major spills of hazardous chemicals, and it focuses on equipment, instrumentation, utilities, human actions, and external factors that might impact the process.
There are a variety of methodologies that can be used to conduct a PHA, including but not limited to: What If? / Checklist, Hazard and Operability Study (HAZOP), and Failure Mode and Effects Analysis. PHA methods are qualitative in nature. The selection of a methodology to use depends on a number of factors, including the complexity of the process, the length of time a process has been in operation, if a PHA has been conducted on the process before, and if the process is unique, or common within the industry. Other methods such as Layer of Protection Analysis (LOPA) or Fault Tree Analysis (FTA) may be used after a PHA if a risk decision wasn’t clear for a given scenario.
In the United States, the use of PHA is mandated by the Occupational Safety and Health Administration (OSHA) in its Process Safety Management regulation for the identification of risks involved in the design, operation, and modification of processes that handle highly hazardous chemicals. We use a variety of approaches to aid in client compliance and upon request, can utilize the following software packages to aid risk management decision making: PHA-Pro, SVA-Pro, FMEA-Pro, PHAWorks 5, LOPAWorks 3, DNV GL – Phast, Safeti, and FLACS CFD.
A Hazard and Operability Study (HAZOP) is a structured and systematic examination of a planned or existing process or operation in order to identify and evaluate problems that may represent risks to personnel or equipment, or prevent efficient operation. HAZOP is a qualitative technique based on guide words and is conducted out by a multi-disciplinary team.
Hazardous Area Classification (HAC) is a method of analyzing and classifying the environment where hazardous atmospheres may occur so as to facilitate the proper selection and installation of equipment to be used safely in that environment. When electrical equipment is used in, around, or near an atmosphere that has flammable gases or vapors, flammable liquids, combustible dusts, or ignitable fibers, there is always a possibility or risk that a fire or explosion might occur. Those areas where the possibility or risk of fire or explosion might occur due to an explosive atmosphere and/or mixture is often called a hazardous (or classified) location/area.
Currently there are two systems used to classify these hazardous areas; the Class/Division system and the Zone system. The Class/Division system is used predominately in the United States and Canada, whereas the rest of the world generally uses the Zone system.
A Hazard Identification (HAZID) is a simple process used to identify hazards in order to plan for, avoid, or mitigate their impacts.
A What-If? Checklist is a brainstorming approach in which a group of people familiar with the process ask questions about possible deviations or failures. These questions may be framed as What-If?, as in “What if the pump fails?” or may be expressions of more general concern, as in “I worry about contamination during unloading.” A scribe or recorder takes down all of the questions on flip charts or a computer. The questions are then divided into specific areas of investigation, usually related to consequences of interest.
A Bow Tie Analysis, a type of qualitative PHA, provides a visual representation of the causes of unintended events, likely outcomes, and measures in place to mitigate or control hazards.
Layers of Protection Analysis (LOPA) is a methodology for hazard evaluation and risk assessment that lies between the qualitative end of the scale (characterized by methods such as hazard and operability HAZOP and What If? Checklist) and the quantitative end (characterized by methods using Fault Tree Analysis and computer consequence modeling). This process is ideally suited for use in combination with a company's risk-decision criteria, such as those displayed in a risk matrix. LOPA is a recognized technique for selecting the appropriate Safety Integrity Level (SIL) of a Safety Instrumented System (SIS) according to the requirements of standards such as ANSI/ISA-84.00.01.
A Failure Mode and Effects Analysis is a methodical study of component failures. This review starts with a diagram of the process that includes all components which could fail and conceivably affect the safety of the process.
A Fault Tree Analysis (FTA) is a quantitative assessment of all of the undesirable outcomes, such as a toxic gas release or explosion, which could result from a specific initiating event. It begins with a graphic representation (using logic symbols) of all possible sequences of events that could result in an incident. The resulting diagram looks like a tree with many branches — each branch listing the sequential events (failures) for different independent paths to the top event. Probabilities (using failure rate data) are assigned to each event and then used to calculate the probability of occurrence of the undesired event.
A PSSR is a safety review conducted prior to startup (commissioning) of a new or modified processing/manufacturing plant or facility to ensure that installations meet the original design or operating intent, to catch and re-assess any potential hazard due to changes during the detailed engineering and construction phase of a project. In other words, it ensures the “Ready for Start-up” status of process facility/units. A Pre Startup Safety Review covers not only equipment, but also procedures and training.
Quantitative Risk Assessment (QRA) software and related methodologies give quantitative estimates of risks, given defined parameters. In the chemical process and petrochemical industries a QRA is primarily concerned with determining the potential consequences caused by undesired events. Specialist software can be used to model the effects of such an event, and to help calculate the potential loss of life. Some organizations use the risk outputs to assess the implied cost to avert a fatality which can be used to set quantified criteria for what is an unacceptable risk and what is tolerable.