CSP – Certified Safety Professional

Process safety management (PSM) prevents or minimizes the consequences of catastrophic releases of toxic, reactive, flammable, or explosive chemicals. OSHA's PSM standard, 29 CFR 1910.119, applies to processes involving a highly hazardous chemical listed in its Appendix A at or above the listed threshold quantity (TQ), and to processes involving 10,000 lb or more of a flammable liquid or gas on site in one location. EPA's Risk Management Program (40 CFR Part 68) applies parallel prevention requirements and adds off-site consequence analysis and public risk management plans.

A process includes any group of vessels that are interconnected, and separate vessels located so that a release could involve them. Notable exclusions include retail facilities, oil and gas well drilling and servicing, normally unoccupied remote facilities, hydrocarbon fuels used solely for workplace consumption (such as propane for comfort heating) when not part of a covered process, and flammable liquids stored in atmospheric tanks or transferred while kept below their normal boiling point without chilling or refrigeration.

PSI is the foundation for every other element; a PHA cannot be valid if the information it analyzes is wrong. PSI has three parts. Hazards of the chemicals include toxicity, permissible exposure limits, physical data, reactivity, corrosivity, thermal and chemical stability, and the hazardous effects of inadvertently mixing different materials (typically drawn from the SDS). Technology of the process includes a block flow diagram or simplified process flow diagram, process chemistry, maximum intended inventory, safe upper and lower limits for temperature, pressure, flow, and composition, and an evaluation of the consequences of deviations. Equipment information includes materials of construction, piping and instrument diagrams, electrical classification, relief system design and design basis, ventilation design, design codes and standards, material and energy balances, and safety systems such as interlocks and suppression.

The PHA identifies, evaluates, and controls the hazards of a covered process. The employer selects a methodology appropriate to the complexity of the process: what-if, checklist, what-if/checklist, hazard and operability study (HAZOP), failure mode and effects analysis (FMEA), fault tree analysis, or an appropriate equivalent. PHAs are prioritized by the extent of the process hazards, number of potentially affected employees, age of the process, and operating history.

• The hazards of the process
• Any previous incident that had a likely potential for catastrophic consequences
• Engineering and administrative controls applicable to the hazards and their interrelationships, including detection methods (process monitoring, alarms, detectors)
• Consequences of failure of engineering and administrative controls
• Facility siting
• Human factors
• A qualitative evaluation of the range of possible safety and health effects of control failures on employees in the workplace

The PHA team must include at least one employee with expertise in engineering and process operations, at least one employee with experience and knowledge specific to the process being evaluated, and one member knowledgeable in the PHA methodology. The employer must have a system to promptly address the team's findings and recommendations, resolve them in a timely manner, document actions taken, and communicate them to affected operating, maintenance, and other employees. Each PHA is updated and revalidated at least every five years so that it is consistent with the current process and incorporates lessons learned, and it is retained for the life of the process.

Management of change (MOC) applies to changes to process chemicals, technology, equipment, procedures, and facilities that affect a covered process. A replacement in kind, meaning a replacement that satisfies the design specification, is not a change. Before implementing a change, the MOC procedure must address the technical basis, the impact on safety and health, modifications to operating procedures, the time period for the change (temporary changes are still changes), and authorization requirements. Affected employees, including contract employees, are informed and trained before start-up of the changed process, and PSI and operating procedures are updated.

A pre-startup safety review (PSSR) is required for new facilities and for modified facilities when the modification is significant enough to require a change in PSI. The PSSR confirms that construction and equipment are in accordance with design specifications; safety, operating, maintenance, and emergency procedures are in place and adequate; a PHA has been performed for new facilities and MOC requirements are met for modified facilities; and training of each employee involved in operating the process is complete.

Every pressure vessel and closed system needs protection against overpressure from credible scenarios: blocked outlet, fire exposure, thermal expansion of trapped liquid, runaway reaction, utility failure (cooling water, power, instrument air), control valve failure, and tube rupture in heat exchangers. Many systems also need vacuum relief to prevent collapse when liquid is pumped out or vapor condenses. Relief device discharges are routed to a safe location such as a flare, scrubber, catch tank, or elevated vent.

Under the ASME Boiler and Pressure Vessel Code (Section VIII), relief valves are set at or below the vessel's maximum allowable working pressure (MAWP). During relief, pressure may rise above MAWP only by the permitted accumulation: 10% for a single device, 16% for multiple devices, and 21% for a fire exposure case.

Chemical compatibility concerns both the reactions between stored or mixed materials and the reaction between a chemical and its container or equipment. Incompatible mixing can produce heat, fire, explosion, toxic gas, or violent polymerization. PSI must document the hazardous effects of inadvertent mixing, and a compatibility matrix (such as a reactivity chart) is used for storage layout, waste consolidation, and transfer-hose and piping design.

Materials of construction must resist the process chemicals at operating temperature and pressure. Examples: hydrofluoric acid attacks glass, so glass sight glasses are unsuitable; wet chlorine rapidly corrodes carbon steel that dry chlorine does not; some elastomers swell or dissolve in solvents, causing gasket and hose failure. Material substitutions require MOC unless they meet the original specification.

Inherently safer design applies PtD thinking to chemical processes. Its four strategies are minimize (intensify: smaller inventories and equipment), substitute (a less hazardous material or chemistry), moderate (attenuate: dilute, refrigerate, or operate at lower temperature and pressure), and simplify (eliminate unnecessary complexity and make errors less likely or easier to correct). Inherent strategies remove or reduce the hazard itself; passive, active, and procedural safeguards then manage what remains, in that order of reliability.