Process safety management guidelines

You must compile complete, accurate written information about the chemicals used in the process, including hazards, reactivity, and effects on equipment. This includes current Safety Data Sheets (SDSs) supplemented with process chemistry details such as runaway reaction and overpressure hazards when applicable, because SDSs alone may not capture process-specific risks. See the guidance in Appendix C to 1910.119 and the main PSM standard 1910.119 for how this information supports PHAs and training.

You should include clear diagrams such as block flow diagrams, process flow diagrams, and Piping & Instrumentation Diagrams (P&IDs) appropriate to users' needs. A block flow diagram gives a simple overview of major equipment and flows; a process flow diagram shows main streams, valves, temperatures and pressures; and P&IDs show detailed relationships between equipment and instrumentation for engineering and maintenance. See the diagram guidance in Appendix C to 1910.119.

Process Safety Information must be documented because multiple users—PHA teams, trainers, operators, contractors, pre-startup reviewers, and emergency planners—rely on it to assess and control hazards. Documenting process limits (e.g., maximum inventory, temperature, pressure) and qualitative consequences of deviations helps teams identify failure modes and design appropriate safeguards. See Appendix C to 1910.119 and the PSM standard at 1910.119.

A PHA is an organized, systematic effort to identify and analyze potential hazards in processes handling highly hazardous chemicals, and you should select PHA methods based on process complexity and how well the process is understood. For stable, well-known processes a checklist or What-If may work; for new or complex processes consider HAZOP or fault-tree analysis. See the PHA description and methodology guidance in Appendix C to 1910.119 and PHA requirements in 1910.119(e)

You must document which codes and standards were used to design process equipment and demonstrate that older equipment built to historical codes remains suitable for its intended use through inspection, testing, and operation records. If your design departs from current codes, document why the alternative design is suitable. See the documentation guidance in Appendix C to 1910.119 and the main 1910.119 for related PSM obligations.

Small businesses can often reduce PSM risk and, in some cases, avoid the PSM threshold by reducing onsite inventories of highly hazardous chemicals below the threshold quantity—for example, ordering smaller shipments or splitting stock across multiple, appropriately separated locations. Dispersing storage so a release at one location won't affect another is a recommended risk-reduction approach. See the inventory and dispersal suggestions in Appendix C to 1910.119 and 1910.119 for applicability.

You must include process-specific chemistry information such as conditions that can lead to runaway reactions, overpressure scenarios, decomposition products, and reactivity with common contaminants because SDSs typically cover only product-level hazards. These process details enable accurate consequence analysis during PHAs. See the chemical information guidance in Appendix C to 1910.119 and the PSM standard 1910.119.

P&IDs should show equipment, instrumentation, valve types and locations, control and safety interlocks, relief devices, and key utilities so engineering and maintenance staff can understand equipment-instrumentation relationships. Including materials of construction, design pressures and temperatures, and control loop components improves clarity for hazard evaluation. See the P&ID guidance in Appendix C to 1910.119.

PHA teams should include people with varied operational and technical backgrounds, and the team leader must be knowledgeable in the chosen PHA methodology and impartial in the evaluation. Team size can range from two people to larger multidisciplinary groups; include subject matter experts as needed. See the PHA team and methodology guidance in Appendix C to 1910.119 and 1910.119(e).

Contractors who work on or near covered processes must be provided process safety information relevant to their work (e.g., hazards, required protective equipment, safe work practices) so they can perform tasks safely. This includes diagrams, P&IDs, and chemical hazard data as appropriate for their scope. See contractor and information-use guidance in Appendix C to 1910.119 and general PSM obligations at 1910.119.

You should document all assumptions, limitations, and reasoning used in the PHA so future teams can understand and reassess the basis for decisions; this includes data uncertainties, boundary conditions, and excluded scenarios. Keeping this record helps ensure continuity and improves future PHAs. See the PHA documentation guidance in Appendix C to 1910.119 and the PHA requirement in 1910.119(e).

Include materials of construction, design pressures and temperatures, pump capacities and pressure heads, compressor horsepower, vessel design ratings, and any manufacturer specifications necessary to evaluate mechanical limits and potential failure modes. This equipment data supports safe operation, maintenance, and PHAs. See the equipment data guidance in Appendix C to 1910.119.

If your process departs from the applicable codes and standards, you must document why the alternative design is suitable for the intended purpose and provide evidence (e.g., engineering analyses, testing) that it meets performance and safety goals. See the guidance on codes, standards, and departures in Appendix C to 1910.119.

Use block flow diagrams to present a high-level view of major equipment and overall flow paths for non-technical audiences, and use process flow diagrams to present more detailed streams, pressures, temperatures, and valve locations for engineers and PHA teams. Choosing the right diagram for the audience improves clarity and hazard analysis. See diagram recommendations in Appendix C to 1910.119.

Including qualitative estimates of consequences (e.g., fire, explosion, toxic release) for deviations beyond limits helps PHAs, emergency planners, and operators evaluate severity and select mitigation measures; without consequence estimates the team cannot prioritize controls effectively. See the guidance on documenting limits and consequences in Appendix C to 1910.119.

Yes. Storing pre-charged equipment that, in aggregate at one site location, contains a Category 1 flammable gas at or above the threshold quantity is a PSM-covered process because storage and on-site movement meet the definition of a "process." OSHA confirmed this in the interpretation on PSM flammable gas aggregation, which explains warehouses with aggregated refrigerant exceeding the 10,000-pound threshold are covered. See the PSM application and aggregation discussion in 1910.119, Appendix C to 1910.119, and the OSHA letter on PSM flammable gas aggregation.

You must keep Process Safety Information current by updating it when process conditions, equipment, or chemicals change; the employer is responsible for maintaining accuracy and ensuring PHA teams, operators, and contractors have current copies. Regular reviews and change control processes help maintain currency. See the importance of accurate written information in Appendix C to 1910.119 and the overall PSM obligations in 1910.119.

Provide emergency planners and local responders with information relevant to emergency scenarios such as hazardous chemical identities, quantities, potential release scenarios, process flow diagrams, and emergency shutdown locations so they can plan response actions. This type of process safety information supports community preparedness described in Appendix C to 1910.119 and the PSM standard 1910.119.

Yes—at least one PHA team member must be familiar with the process, and the team should include people who bring expertise in process technology, design, operating procedures and actual work practices. See 1910.119(e) and the guidance in 1910.119AppC which recommends members with expertise in alarms, emergency procedures, instrumentation, maintenance procedures (routine and nonroutine), procurement, safety and health, and any other relevant subject.

• Include a competent team leader who can manage the study and forge consensus.
• Use team members (full- or part-time) whose combined knowledge covers design, operations, maintenance, and safety.

Yes—an employer may use different PHA methodologies for various parts of a process and then integrate the conclusions into one final study. The guidance in 1910.119AppC explicitly states that different methodologies and team members can be used for unit operations of varying size, age, or complexity and that their conclusions should be integrated into the overall evaluation.

• This is practical when segments differ (e.g., distillation vs. blending) or when some units justify a more detailed method while others use checklists.
• Make sure integration addresses interfaces and combined hazards.

It is acceptable to use a generic or checklist PHA when the processes are standard, not unique, or when the plant is movable or multiple similar sites exist—provided variations at each site are accounted for. 1910.119AppC gives examples such as standard boilers, heat exchangers, movable gas plants, or multiple similar gas plants where no sour gas is processed.

• For batch operations, a representative generic PHA can be used when ingredient ratios change only slightly and the chemistry is documented for the full range.
• Small businesses with less complex processes may appropriately use simpler methods or checklists as noted in 1910.119AppC.

Employers should prioritize PHAs by considering potential severity of a chemical release, number of potentially affected employees, operating history (frequency of releases), process age, and other relevant factors to rank processes by risk. 1910.119AppC recommends using a preliminary or gross hazard analysis and suggests weighting or systematic ranking methods.

• Give first consideration to processes that could affect the largest number of employees.
• Document the prioritization method (weighing factors or ranking) so decision-making is auditable.

Operating procedures must clearly state the tasks to be performed, data to record, operating conditions to maintain, sampling, safety precautions, and instructions for upset, startup, and shutdown conditions. 1910.119AppC says procedures should be technically accurate, understandable, reviewed by engineering and operations staff, and revised periodically to reflect current operations.

• Include explicit pressure/temperature limits, flow rates, alarms to monitor, and step-by-step directions for upset, startup and shutdown situations.
• Make sure instructions distinguish normal from startup/shutdown parameters and explain how to ramp equipment safely.

Operating instructions must describe the control system logic and the relationship between software and equipment so operators understand system behavior. 1910.119AppC notes that computerized control systems add complexity and that the logic should be explained to prevent operator confusion.

• Document control sequences, interlocks, automatic actions, alarm meanings, and manual override procedures.
• Train operators on simulator or walkthroughs that reflect the actual control logic whenever feasible.

Employers must provide operating procedures and instructions in a language the workers are fluent in when workers are not fluent in English. 1910.119AppC explicitly states procedures and instructions should be available in a second language understood by the workers.

• Translate critical procedures and provide bilingual training, signs, and checklists as needed.
• Ensure comprehension through evaluation (e.g., hands-on demonstration or tests).

Operating procedures must be revised whenever process changes occur through management of change, and impacted personnel must be oriented to the changes before startup. 1910.119AppC requires evaluation of the consequences of changes (including subtle mechanical changes) and coordination of management of change actions with current procedures.

• Update written procedures before restarting the process after a shutdown for change implementation.
• Train affected employees on new procedures and document their understanding prior to startup.

Training must make employees fully understand the hazards of chemicals and processes, and must cover Hazard Communication basics plus operating procedures, safety work practices, emergency response, and routine/nonroutine task authorization. 1910.119AppC references training under 1910.1200 as a foundation but requires additional process safety topics.

• Define who must be trained and the subjects for each employee group.
• Include emergency evacuation, upset condition handling, and SDS literacy.

Employers should write clear, measurable learning goals and objectives for each training module before training begins and define the actions or conditions that demonstrate competence. 1910.119AppC recommends tailoring objectives to specific modules and describing acceptable performance.

• Document performance criteria (e.g., correct simulator response, checklist completion).
• Use those criteria to evaluate trainees and determine need for retraining or refresher courses.

Hands-on training using simulators or realistic controlled environments is effective for teaching operators how to handle upset conditions and control-room tasks. 1910.119AppC specifically recommends simulated control panels and upset-condition scenarios to let trainees practice responses safely.

• Use practical exercises, role-playing, and simulator drills for rare but critical events.
• Combine with written tests or observed performance to verify competence.

Employers must periodically evaluate training programs and provide retraining or more frequent refreshers until deficiencies are corrected; training must also be updated when processes change. 1910.119AppC requires evaluation methods be developed with training goals and objectives to measure understanding and skill retention.

• Reevaluate after incidents, near misses, or procedure changes.
• Document evaluations, retraining actions, and outcomes.

Contractors must be trained so they understand the hazards of the chemicals and processes and the site's safety procedures; employers must screen contractors for safety performance and qualifications before hire. 1910.119AppC states that contractors need appropriate job skills, certifications, and that their work methods and safety history be evaluated.

• Obtain contractor injury/illness rates and references when safety performance is unknown.
• Ensure contractors are briefed on site-specific hazards, permit and authorization procedures, and emergency actions.

Yes—maintaining a site log of contractor injury and illness history helps the employer track contractor performance and manage safety risks. 1910.119AppC recommends keeping such logs as a method to maintain current knowledge of contractor activities around covered processes.

• Use logs to inform future contractor selection and on-site supervision needs.
• Integrate contractor performance into your contractor management program.

A checklist PHA is appropriate for standard, well-understood equipment such as boilers or heat exchangers where hazards are common and predictable; the Appendix gives this as an explicit example. See 1910.119AppC.

• Use detailed checklists prepared from industry codes and past experience.
• Ensure that site-specific deviations (age, materials, modifications) are considered and documented.

An employer may perform separate PHAs for each segment (e.g., distillation tower, blending operation) and then integrate the results into a comprehensive evaluation. 1910.119AppC explicitly supports segmenting large processes for analysis and then combining conclusions.

• Make sure cross-segment interfaces, alarm interactions, and shared utilities are analyzed in integration.
• Document how segment PHAs were combined and how any residual risks were addressed.

Yes—storage of pre-charged equipment that results in an aggregate quantity of a Category 1 flammable gas on site in one location can be a PSM-covered process when it meets or exceeds the threshold quantity. The PSM standard defines "process" to include storage and on-site movement; see 1910.119 and the June 6, 2024 Letter of Interpretation on PSM flammable gas aggregation.

• If your warehouse stores pre-charged units and the aggregated refrigerant amount in one location ≥ 10,000 lb, PSM applies.
• Evaluate storage, on-site movement (forklifts), inventory practices, and implement PSM elements (e.g., PHA, MOC) as required.

Yes—employer associations may develop generic PHAs (evolved from checklists or what‑if questions) for members with common, simple processes so long as each employer adapts the generic PHA to reflect their particular process. 1910.119AppC gives the example of multiple members operating similar cold storage or water treatment facilities.

• Each employer must account for site-specific differences and document adaptations.
• Generic PHAs can simplify compliance for small businesses but must remain accurate for the particular site.

PHA teams should work together, use the expertise of members and outside experts as needed, and the team leader should manage discussions to resolve issues and forge consensus on findings and recommendations. 1910.119AppC emphasizes team compatibility and a team leader capable of managing the study.

• Document dissenting opinions and the rationale for final decisions when full consensus is not possible.
• Consider external technical review if internal expertise is insufficient.

Under 1910.119 and its Appendix C, yes — employers should use injury and illness logs that include both their own employees and contract employees who work on or near a covered process so the employer has full knowledge of process-related incidents.

• Appendix C explains that logs for both employer and contract workers provide useful information for PSM audits and incident investigations; see 1910.119AppC.
• The PSM standard itself, 1910.119, requires employers to know their process hazards and maintain records that support safe operation.

Keeping contract employee injury and illness records helps coordinate contractor activities, improves incident investigation quality, and supports compliance and audit efforts.

Under 1910.119 and Appendix C, yes — employers should implement a permit or work authorization system for contractors performing specialized or hazardous tasks (for example, confined space entry or nonroutine repairs) to control activities and improve coordination.

• Appendix C recommends a permit or work authorization system to keep the host employer informed of contractor activities and to provide management control; see 1910.119AppC.
• This procedure should coordinate applicable controls such as lockout/tagout, line-breaking, hot work, and confined-space requirements in accordance with the overall PSM program in 1910.119.

A written permit system clarifies hazards, required protections, and closure steps so contractors and operations staff share the same expectations and responsibilities.

Under 1910.119(e) and Appendix C, employers must complete a pre-startup safety review (PSR) that verifies P&IDs, operating procedures, training, and implementation of PHA recommendations before placing a new process into service.

• The standard requires a pre-startup safety review; see 1910.119(e).
• Appendix C explains that PHA recommendations should be used to improve design, P&IDs must be completed, operating procedures developed, and operating staff trained prior to startup; see 1910.119AppC.

Practical steps include completing and verifying P&IDs, finalizing written operating and startup procedures, training operators on those procedures, and resolving PHA findings before final installation and startup.

Under 1910.119 and Appendix C, employers must apply management of change (MOC) procedures to any changes made during shutdowns or turnarounds that are more than "replacement in kind," and must update P&IDs, operating procedures, and training as necessary before restart.

• Appendix C states that changes other than "replacement in kind" during shutdown require going through MOC procedures and that P&IDs, procedures, and training should be updated as needed; see 1910.119AppC.
• The general MOC requirements are part of the PSM program in 1910.119.

If changes are significant or affect training or operating parameters, provide refresher or additional training, review incident investigation and PHA recommendations for impacts, and perform pre-startup checks before returning to normal operations.

Under 1910.119 and Appendix C, an effective mechanical integrity program must identify and categorize covered equipment and instrumentation, set inspection and testing frequencies, develop maintenance procedures, train maintenance personnel, establish acceptance criteria, and document test and inspection results.

• Appendix C lists these elements explicitly, including equipment categorization, inspections and tests, testing frequencies, maintenance procedures, training, acceptance criteria, and documentation; see 1910.119AppC.
• These mechanical integrity activities support compliance with the PSM standard at 1910.119.

Practical tips:

• Use manufacturer data and operating experience to set meantime-to-failure and inspection intervals.
• Keep records that tie inspections/tests to corrective actions.
• Ensure maintenance workers receive training on safe procedures and special tools.

Under 1910.119 and Appendix C, employers should prioritize equipment and instrumentation for closer scrutiny based on their risk (e.g., pressure vessels, relief systems, piping), the material's corrosion/erosion rates, manufacturer meantime-to-failure data, and operating experience.

• Appendix C advises compiling and categorizing equipment (pressure vessels, storage tanks, piping, relief systems, alarms, pumps, etc.) and prioritizing pieces that require closer scrutiny; see 1910.119AppC.
• Applicable codes and standards (e.g., NBIC, API, ASME) help establish inspection frequencies and methodologies as noted in Appendix C and support compliance with 1910.119.

Use corrosion-rate data (or conservative maximum frequencies if unknown), manufacturer recommendations, and the consequences of failure to set inspection priorities and frequencies.

Under Appendix C to 1910.119, internal inspections should examine vessel shells, bottoms, heads, metallic and nonmetallic linings, measure thicknesses, and check for erosion, corrosion, cracking, bulges, and internal component damage (trays, baffles, sensors, screens).

• Appendix C describes the internal inspection scope, including thickness measurements and checks for erosion, corrosion, cracking, bulges, and internal equipment deficiencies; see 1910.119AppC.
• Those inspection procedures support the mechanical integrity obligations in 1910.119.

Ensure inspection procedures are consistent (even when multiple inspectors are used), provide training for maintenance personnel on these procedures, and document inspection findings and corrective actions.

Under Appendix C to 1910.119, employers should retain "as-built" drawings, certifications of coded vessels, materials of construction verification, installation inspection records, and supplier audits when necessary to document that proper materials and procedures were used.

• Appendix C states that "as built" drawings plus certifications and material verification should be retained in quality assurance documentation and that field inspections should verify correct materials and qualified craftsmen; see 1910.119AppC.
• These records support the PSM program requirements in 1910.119.

Include verification of gaskets, bolts, welding rods, torque of safety devices, pump seal installation, and any supplier audits needed to ensure purchased parts are suitable for service. Route any equipment changes through management of change procedures.

Under Appendix C to 1910.119, a nonroutine work authorization must provide a clear procedure for obtaining clearance, communicate identified hazards to those doing the work and affected operating personnel, and coordinate applicable controls such as lockout/tagout, line breaking, confined-space and hot work procedures.

• Appendix C recommends a work authorization notice or permit that outlines steps the maintenance supervisor, contractor representative, or other responsible person must follow to obtain necessary clearances; see 1910.119AppC.
• The permit system should reference and coordinate with related controls and procedures under the PSM program in 1910.119.

A complete permit should also include requirements for closing out the job, notifying affected personnel that work is complete, and steps to return equipment to normal operation.

Under 1910.119 and Appendix C, "change" means modifications to equipment, procedures, raw materials, and processing conditions other than "replacement in kind," and temporary changes are covered by the management of change procedures and must have time limits and monitoring.

• Appendix C defines change broadly and explicitly states that temporary changes are subject to MOC and that employers should establish ways to detect and control temporary changes and return equipment to original conditions after the temporary period; see 1910.119AppC.
• MOC requirements are part of the PSM obligations in 1910.119.

Employers should document temporary change duration, authorization, safety reviews, and a plan to revert to original conditions to prevent temporary modifications from becoming inadvertent permanent hazards.

Under 1910.119 and OSHA's June 6, 2024 interpretation, yes — storage of pre-charged appliances that together contain a Category 1 flammable gas on site in one location that exceeds the 10,000-pound threshold is a PSM-covered process.

• OSHA's interpretation addressing aggregation of Category 1 flammable gases concludes that storage and on-site movement of pre-charged air conditioners in a warehouse meet the PSM definition of a "process" when the aggregate quantity on site in one location equals or exceeds the 10,000-pound threshold; see the letter of interpretation "PSM flammable gas aggregation" and 1910.119.
• The Hazard Communication definitions in 1910.1200 are used to determine Category 1 flammable gases.

If your operation stores aggregate quantities at or above the threshold, implement the PSM elements (PHA, MOC, mechanical integrity, emergency response, etc.) required by 1910.119.

Under Appendix C to 1910.119, a typical MOC form should document the description and purpose of the change, technical basis, safety and health considerations, affected documents (P&IDs, operating and maintenance procedures), training needs, pre-startup inspection, duration if temporary, and approvals.

• Appendix C provides an example list of what an MOC form may include, such as change description, technical basis, safety considerations, documentation updates, training, pre-startup inspection, duration, and approvals; see 1910.119AppC.
• These MOC records support the PSM requirements in 1910.119.

Use a checklist approach for minor well-understood changes and a fuller hazard evaluation and multi-discipline approvals (operations, maintenance, safety) for complex or significant changes.

Under 1910.119 App C, employers should assemble a trained, multidisciplinary team that includes people familiar with the process and employees from the area where the incident occurred and follow a fact‑finding, no‑blame investigation to identify root causes and implement corrective actions.

• Team composition and selection

  • Include a trained lead investigator and team members chosen for their training, knowledge, and ability to contribute to the investigation (for example: process engineers, maintenance, operations, safety staff, and others as needed) as recommended in the PSM guidance in 1910.119 App C.
  • Consult, interview, or include employees from the process area where the incident or near‑miss occurred; their firsthand knowledge is important.

• Investigation steps employers should take

  • Treat events that result in—or could reasonably have resulted in—a catastrophic release (including near‑misses) as incidents to investigate, per the App C guidance.
  • Train investigators in interview techniques, documentation, and report writing before they conduct investigations.
  • Gather facts through scene inspection, equipment and document review, and witness interviews; focus on identifying how and why the event happened rather than assigning blame.
  • Develop plausible scenarios and determine root and contributing causes.
  • Recommend and document corrective actions, assign responsibility, set timetables, and track completion.
  • Share the investigation report, findings, and lessons learned with employees and others who can benefit from the information, as the App C guidance directs.

• Why this matters

  • Building in‑house investigative capability and following these steps helps prevent repeat incidents and supports compliance with the PSM program requirements in 1910.119.

(See the PSM guidance in 1910.119 App C and the PSM standard at 1910.119 for additional details.)