PSM Glossary

The list of 137 highly hazardous chemicals (HHCs) — with their threshold quantities (TQs) — found in OSHA's PSM standard. If a facility handles any Appendix A chemical at or above its TQ in a single process, the process is covered by 29 CFR 1910.119. Regulation: 29 CFR 1910.119, Appendix A

A storage tank designed to operate at pressures from atmospheric through 0.5 psig (1910.119(b)). Flammable liquids stored in atmospheric tanks, and kept below their normal boiling point without chilling or refrigeration, are excepted from the 10,000-lb flammables trigger. The exception does not apply to Appendix A chemicals, and OSHA has said it does not reach tanks connected to a covered process. Regulation: 29 CFR 1910.119(a)(1)(ii)

A formal, periodic assessment of whether a facility's PSM program procedures and practices are adequate and are actually being followed. Required at least every three years under 1910.119(o). Not the same as an OSHA inspection. Regulation: 29 CFR 1910.119(o)

A hazard analysis technique that identifies barriers (safeguards) between a hazard and a potential loss event. Used to evaluate whether existing protections are adequate. Related to bow-tie analysis.

A simplified diagram showing the major process blocks and the flow of materials between them. Less detailed than a Process Flow Diagram (PFD) or P&ID. Required as part of Process Safety Information under 1910.119(d). Regulation: 29 CFR 1910.119(d)(2)(i)(A)

A risk analysis method that visually maps the causes of a hazardous event (left side) and its consequences (right side), with safeguards shown on each side. Increasingly used in PSM programs alongside or in place of traditional PHA methods.

A major uncontrolled emission, fire, or explosion involving one or more highly hazardous chemicals that presents serious danger to employees in the workplace. The trigger for PSM incident investigation requirements. Regulation: 29 CFR 1910.119(b)

A PHA methodology using a structured list of items to verify that a process or system meets established safety criteria. Simpler than HAZOP; best suited for straightforward processes or as a supplement to more rigorous methods. Regulation: 29 CFR 1910.119(e)(2)

Evaluation of the potential outcomes of an accidental chemical release — including dispersion modeling, fire/explosion effects, and toxic exposure zones. Used in PHAs and facility siting studies.

A process that contains an Appendix A chemical at or above its threshold quantity, or 10,000 lb or more of a covered flammable liquid or gas, is not otherwise excluded by the standard, and therefore must comply with all 14 elements of 29 CFR 1910.119. Regulation: 29 CFR 1910.119(a)

A subsonic combustion reaction — a flame that propagates through a flammable mixture at less than the speed of sound. Distinguished from detonation. Deflagrations can still cause significant overpressure and structural damage.

A supersonic combustion reaction that propagates at greater than the speed of sound through an explosive mixture, producing a powerful shock wave. More destructive than deflagration. Can be triggered by deflagration-to-detonation transition (DDT).

Computer modeling of how a released chemical would spread through the air under specific weather and terrain conditions. Used to determine toxic and flammable hazard zones and for emergency planning.

A written plan, required under 29 CFR 1910.38 and incorporated by reference into the PSM standard, that describes what employees must do in the event of a fire, hazardous chemical release, or other emergency. PSM adds a requirement that the EAP address small releases of HHCs. Regulation: 29 CFR 1910.119(n); 1910.38

A written document required by 1910.119(c) describing how the employer will involve employees in the development and implementation of PSM elements, particularly process hazard analyses. Regulation: 29 CFR 1910.119(c)

The manner in which a piece of equipment fails — e.g., fails open, fails closed, fails to start, leaks. Identifying failure modes is a key step in FMEA and HAZOP analyses.

The consideration of the geographic placement of equipment, control rooms, occupied buildings, and other structures relative to process hazards. PSM requires that PHAs address facility siting — particularly the vulnerability of occupied buildings to explosion overpressure or toxic releases. Regulation: 29 CFR 1910.119(e)(3)(v)

A systematic, bottom-up methodology for identifying how individual components can fail and what effect each failure has on the overall process or system. One of the PHA methodologies listed under 1910.119. Regulation: 29 CFR 1910.119(e)(2)

A top-down, deductive analysis method that models the logical combinations of events and faults that could lead to a defined undesired event (the "top event"). One of the PHA methodologies listed. Regulation: 29 CFR 1910.119(e)(2)

Under PSM, a flammable liquid with a flashpoint below 100°F (37.8°C) or a Category 1 flammable gas — when present in a process in quantities of 10,000 lbs or more, the process is covered by PSM even if not on the Appendix A list. Regulation: 29 CFR 1910.119(a)(1)(ii)

The lowest temperature at which a liquid produces enough vapor to ignite momentarily when exposed to a spark or open flame. Important for classifying flammable liquids and determining PSM applicability.

Section 5(a)(1) of the OSH Act, which requires employers to provide a workplace free from recognized hazards likely to cause death or serious injury. OSHA cites the GDC for PSM-related hazards at facilities not covered by 1910.119, or for gaps not addressed by specific standards. Regulation: OSH Act Section 5(a)(1)

In HAZOP analysis, a guideword is a simple word or phrase (e.g., NO, MORE, LESS, AS WELL AS, REVERSE, OTHER THAN) applied to each process parameter to prompt systematic identification of possible deviations from design intent.

The most widely used PHA methodology in the chemical and refining industries. A structured, team-based examination of a process using guidewords applied to process parameters (flow, temperature, pressure, etc.) to identify deviations, their causes, consequences, and safeguards. One of OSHA's approved PHA methods. Regulation: 29 CFR 1910.119(e)(2)

A broad, early-stage technique for identifying potential hazards in a process, often conducted before more detailed analysis methods (like HAZOP) are applied. Less formal than PHA but useful for new designs.

A substance defined by OSHA as posing a serious hazard — listed in Appendix A of 1910.119 (with threshold quantities), or flammable liquids/gases in quantities of 10,000 lbs or more. PSM applies when HHCs are present in covered processes. Regulation: 29 CFR 1910.119(b)

Any work involving open flames, welding, cutting, burning, heating, or other ignition sources performed on or near a covered process. Requires a written Hot Work Permit under 1910.119(k). Regulation: 29 CFR 1910.119(k)

Consideration of how human capabilities, limitations, and behaviors affect process safety. PSM requires that PHAs address human factors — particularly the likelihood and effect of human error in operating the process. Regulation: 29 CFR 1910.119(e)(3)(vi)

A safeguard, device, or system that is capable of preventing a hazard scenario from reaching its undesired consequence, independently of other protection layers. IPLs must be independent, effective, and auditable. Central to LOPA methodology.

An approach to chemical process design that eliminates or reduces hazards at the source — by using safer chemicals, smaller inventories, milder operating conditions, or simpler processes — rather than adding safeguards to control hazards.

Periodic examination and functional testing of process equipment to verify mechanical integrity. Required under 1910.119(j) at intervals consistent with manufacturer recommendations or recognized engineering standards (e.g., API 510, API 570). Regulation: 29 CFR 1910.119(j)(4)

An automatic system that initiates a corrective or protective action when a process variable exceeds a defined limit — e.g., a high-pressure interlock that closes a valve when pressure exceeds the setpoint. Often part of a Safety Instrumented System (SIS).

A semi-quantitative risk analysis method that estimates the frequency of a hazardous scenario after accounting for independent protection layers (IPLs). Used to determine whether existing safeguards are sufficient or additional layers are required. Often follows a HAZOP.

Lower Explosive Limit (LEL) or Lower Flammable Limit (LFL) — the minimum concentration of a gas or vapor in air below which ignition cannot occur. Important for gas detection system setpoints and ventilation design.

A community-level emergency planning body established under EPCRA (Emergency Planning and Community Right-to-Know Act). Facilities subject to EPA's RMP Rule must coordinate with LEPCs. PSM facilities often coordinate with LEPCs as part of emergency planning.

The formal process required by 1910.119(l) for reviewing and authorizing changes to process chemicals, technology, equipment, procedures, or facilities before those changes are implemented. Does not apply to replacement in kind. Regulation: 29 CFR 1910.119(l)

The PSM element (1910.119(j)) requiring written maintenance procedures, training, inspection, and testing programs to ensure that process equipment is fit for service and will not fail in a manner that could cause a hazardous chemical release. Regulation: 29 CFR 1910.119(j)

Material Safety Data Sheet (legacy) / Safety Data Sheet (current GHS format). Written documentation of a chemical's hazard information. Acceptable as partial fulfillment of the chemical hazard information requirement under PSI (1910.119(d)(1)). Regulation: 29 CFR 1910.119(d)(1)

OSHA's targeted inspection program that directs compliance officers to focus on specific hazardous industries or standards. The PSM NEP focuses on petroleum refineries, chemical facilities, and other high-hazard industries covered by 1910.119.

An unplanned event that did not result in injury or release but had the potential to do so. PSM requires investigation of incidents that "could reasonably have resulted in a catastrophic release" — meaning near-misses must be investigated, not just actual incidents. Regulation: 29 CFR 1910.119(m)(1)

In HAZOP analysis, a node is a defined section of the process — typically a line, vessel, or piece of equipment — that is examined systematically by applying guidewords to each relevant process parameter.

The safe upper and lower boundaries for critical process parameters (temperature, pressure, flow, composition, level) within which a process must be operated. Required as part of PSI and operating procedures, with documented consequences for exceeding limits. Regulation: 29 CFR 1910.119(d)(2)(i)(D); 1910.119(f)(1)(ii)

Written instructions covering all phases of process operation (startup, normal operation, temporary operation, emergency shutdown, emergency operation, normal shutdown, startup after turnaround). Required under 1910.119(f) and must be certified annually as current. Regulation: 29 CFR 1910.119(f)

Piping and Instrumentation Diagram — a detailed schematic showing process piping, equipment, instrumentation, and control systems. A core document under Process Safety Information (1910.119(d)). P&IDs must reflect actual field conditions and be updated after changes. Regulation: 29 CFR 1910.119(d)(3)(i)(B)

Process Flow Diagram — a diagram showing the major process equipment, streams, and basic material/energy balances. Less detailed than a P&ID. Required as part of Process Safety Information. Regulation: 29 CFR 1910.119(d)(2)(i)(A)

The required update of an existing Process Hazard Analysis at least every five years from the date of the previous study. The revalidation must address changes to the process, resolve prior recommendations, and be conducted by a qualified team. Regulation: 29 CFR 1910.119(e)(6)

A formal safety review required before introduction of a highly hazardous chemical to a new or significantly modified process. Must confirm construction matches design, procedures are in place, PHA recommendations are resolved, and training is complete. Regulation: 29 CFR 1910.119(i)

See PFD above.

A systematic, team-based evaluation of potential hazards in a covered process, using a methodology listed in the standard (HAZOP, What-If, FMEA, FTA, etc.). Required under 1910.119(e) and must be revalidated every five years. Regulation: 29 CFR 1910.119(e)

The written compilation of chemical hazard data, process technology information, and process equipment information required by 1910.119(d) as the foundation for the PHA and all other PSM elements. Regulation: 29 CFR 1910.119(d)

OSHA's Process Safety Management standard (29 CFR 1910.119) — a comprehensive regulatory framework of 14 elements designed to prevent the unintentional release of toxic, reactive, flammable, or explosive chemicals from covered processes. Regulation: 29 CFR 1910.119

Risk assessment using descriptive scales (e.g., low/medium/high) rather than numerical probability values. HAZOP-based PHAs are typically qualitative. Contrasted with semi-quantitative (LOPA) and fully quantitative (QRA) methods.

A detailed risk assessment that estimates the numerical probability and consequences of hazardous scenarios to calculate risk metrics (e.g., individual risk, societal risk). More resource-intensive than HAZOP or LOPA; typically used for major new facilities or high-consequence scenarios.

Standards, practices, and guidelines established by recognized industry organizations (API, ASME, NFPA, AIChE, etc.) that define accepted practices for the design, operation, and maintenance of process equipment. OSHA references RAGAGEP as the standard for MI inspection and testing under 1910.119(j). Regulation: 29 CFR 1910.119(d)(3)(ii); 1910.119(j)(4)(ii)

A pressure-relieving device — such as a pressure relief valve (PRV), rupture disk, or pressure safety valve (PSV) — designed to open at a set pressure to prevent overpressure of a vessel. Relief system design basis is required as part of PSI under 1910.119(d). Regulation: 29 CFR 1910.119(d)(3)(i)(D); 1910.119(j)(1)(iii)

Defined in 1910.119(b) as "a replacement which satisfies the design specification." RIK does not require a Management of Change review under PSM. Determining what qualifies as "in kind" requires careful judgment. Regulation: 29 CFR 1910.119(b); 1910.119(l)(1)

EPA's chemical accident prevention program (40 CFR Part 68), which parallels and overlaps with OSHA's PSM standard. Many PSM-covered facilities must also comply with RMP. Both require hazard assessments, prevention programs, and emergency response plans. Regulation: 40 CFR Part 68

A systematic process for identifying the underlying causes of an incident or near-miss, going beyond immediate causes to find the systemic failures that allowed the event to occur. The standard requires the investigation report to identify the factors that contributed to the incident (1910.119(m)(4)(iv)); a formal RCA method is a common way to meet that. Regulation: 29 CFR 1910.119(m)(4)(iv)

See Operating Limits. The upper and lower process parameter boundaries (temperature, pressure, flow, level, composition) within which the process must be maintained. Deviations outside SOLs may trigger alarms, interlocks, or emergency actions.

A specific function implemented by a Safety Instrumented System (SIS) to bring a process to a safe state when a predetermined condition is violated. Each SIF has a defined Safety Integrity Level (SIL) requirement.

A system composed of sensors, logic solvers, and final elements designed to take a process to a safe state when predetermined conditions are violated. SIS design and testing is governed by IEC 61511 and ISA 84. Part of the safety layer for high-hazard processes.

A discrete performance level (SIL 1 through SIL 4) that defines the required reliability of a Safety Instrumented Function. Higher SIL levels require greater reliability and more rigorous testing. SIL determination is often done using LOPA.

The minimum quantity of a highly hazardous chemical that triggers PSM coverage when present in a single process. TQs are listed in Appendix A of 1910.119 and vary by chemical based on toxicity, flammability, and reactivity hazards. Regulation: 29 CFR 1910.119, Appendix A

Confidential business information — such as a proprietary chemical formula or process design — that an employer may claim is trade secret. Under 1910.119(p), trade secret status cannot be used to withhold information from the people compiling process safety information, conducting PHAs, writing operating procedures, or handling incident investigations, emergency planning, and compliance audits; employers may require confidentiality agreements.Regulation: 29 CFR 1910.119(p)

Upper Explosive Limit (UEL) or Upper Flammable Limit (UFL) — the maximum concentration of a gas or vapor in air above which ignition cannot occur (mixture is too rich). Between the LEL and UEL is the flammable range.

An explosion resulting from the ignition of a flammable vapor cloud that has formed from a release of gas or volatile liquid. VCEs are responsible for some of the most destructive process safety incidents on record, including Texas City (2005) and Buncefield (2005).

A system designed to safely route process fluids (gases, vapors, or liquids) away from a process when pressure relief devices open. Vent system design basis is required as part of PSI under 1910.119(d). Regulation: 29 CFR 1910.119(d)(3)(i)(D); 1910.119(j)(1)(iii)

A PHA methodology using structured brainstorming to identify hazards by posing "What if...?" questions about the process. Simpler and faster than HAZOP; best suited for less complex processes or as a supplement to other methods. Listed PHA methodology. Regulation: 29 CFR 1910.119(e)(2)

A hybrid PHA methodology combining the brainstorming approach of What-If Analysis with the structured verification of a Checklist Analysis. One of the PHA methodologies listed under 1910.119(e)(2). Regulation: 29 CFR 1910.119(e)(2)

In the context of EPA's Risk Management Program (RMP), the release scenario that would result in the greatest distance to a toxic endpoint or the largest explosion or fire. Required for RMP offsite consequence analysis. PSM does not specifically require worst-case scenario analysis, though it informs PHA consequence evaluation. Regulation: 40 CFR 68.25

The classification of hazardous areas where flammable gases, vapors, or combustible dusts may be present, determining the type of electrical equipment that may be safely used. Covered under NEC Article 500-506 and IEC standards. Electrical area classification drawings are part of PSI under 1910.119(d). Regulation: 29 CFR 1910.119(d)(3)(i)(C)