Complete Guide to Process Safety Management Risk Assessments: When to Use Each Method
In the process industries, the prevention of hazardous events relies on systematic risk evaluations carried out throughout the lifecycle of a project. From early concept development to operational changes and regulatory compliance, each assessment serves a distinct function in managing potential hazards. A well-defined risk assessment strategy provides clarity on process safety requirements, supports engineering decisions, and aids in the identification and mitigation of operational threats before they escalate.
This guide outlines some of the primary types of risk assessments used in process safety and explains their purpose at different stages of a facility’s development and operation. It is intended to help engineers, project managers, and safety professionals to apply the appropriate assessment tools at the right time.
Before the Project is Started- Preliminary Risk Analysis (PRA)
Before the Capital Appropriation Request is Submitted – Basis of Safety Study (BOSS)
Before Construction – Detailed Design and Risk Validation
Before Commissiong – Pre-Startup Safety Review (PSSR)
After Commissioning but Prior to Changes (MoC)
During Operation and Beyond
Preliminary Risk Analysis (PRA) is performed during the earliest stages of project planning. This qualitative evaluation allows teams to identify hazards associated with proposed technologies, raw materials, and process configurations. It provides an initial risk profile that helps compare options before committing to a specific process route.
Typical Outputs of PRA:
- Identification of process steps with inherent hazards such as thermal runaway, high reactivity, or toxic exposure
- Early assessment of flammable, explosive, or unstable material risks
- Evaluation of alternative designs based on inherent safety principles
Conducting a PRA helps eliminate high-risk technologies before they reach the design phase, thereby minimizing the likelihood of future revisions or costly retrofits. While PRA is typically qualitative, it sets the foundation for further, more detailed assessments.
Before the Capital Appropriation Request is Submitted – Basis of Safety Study (BOSS)
The Basis of Safety Study (BOSS) is an equipment-focused risk evaluation typically conducted before submitting a capital expenditure request. At this stage, the design has progressed enough to allow for identification of credible hazard scenarios and associated safety measures. BOSS is used to outline how the process will be operated safely under normal and abnormal conditions.
Focus Areas Include:
- Fire and explosion hazards from combustible dust, flammable vapors, or gas leaks
- Loss of containment events due to mechanical failure or corrosion
- Pressure excursions including vacuum collapse or overpressure in vessels and pipelines
- Identification of engineered safeguards, such as pressure relief systems, isolation valves, and inerting systems
By defining risk scenarios and corresponding protective measures, the BOSS provides a technical basis for 70%–90% of the safety-related portion of the capital budget.
Before Construction - Detailed Design and Risk Validation
During the design phase, the process is developed into more detailed documentation such as piping and instrumentation diagrams (P&IDs), control philosophies, and operating procedures. At this stage, formal hazard identification and risk reduction techniques are applied.
Two industry-standard methods are typically used together:
- HAZOP (Hazard and Operability Study): A structured, guideword-driven approach to identify deviations from design intent and their potential consequences. It covers operational, procedural, and control-related issues.
- LOPA (Layer of Protection Analysis): A semi-quantitative method to evaluate whether risk reduction measures meet acceptable criteria. It calculates the likelihood of incidents based on the independence and reliability of safety barriers.
Integration of HAZOP and LOPA Yields:
- Clear understanding of failure mechanisms, initiating events, and consequence severity
- Quantified assessment of independent protection layers such as interlocks, alarms, and emergency shutdown systems
- Documentation of risk acceptance decisions based on company-specific tolerability criteria
This phase confirms whether design safeguards are sufficient to control identified hazards, while maintaining alignment with safety integrity level (SIL) requirements, if applicable.
Before Commissiong – Pre-Startup Safety Review (PSSR)
Prior to introducing hazardous materials or beginning operations, a Pre-Startup Safety Review (PSSR) is conducted. The PSSR verifies that the process installation is consistent with the intended design, and that operational and safety systems are functional.
Key Elements of PSSR:
- Equipment installation matches engineering specifications
- Control systems are calibrated, functional, and tested
- Procedures for normal operations, emergencies, and shutdown are documented and accessible
- Training has been completed for operators and maintenance staff
PSSR functions as a final confirmation step, closing the loop between risk assessment and physical implementation. Any discrepancies are addressed before moving forward, avoiding start-up under unsafe conditions.
After Commissioning but Prior to Changes (MoC)
After startup, processes often undergo changes to improve efficiency, increase capacity, or replace aging equipment. The Management of Change (MoC) process evaluates the safety implications of any proposed changes that could affect process conditions, chemical compatibility, or safety systems.
MoC Assessments Address:
- Impact on process parameters such as temperature, pressure, and flow rates
- Compatibility of new materials or components with the existing system
- Whether existing hazard assessments remain valid after changes
- Need for revalidation of safeguards or procedural updates
MoC prevents unintended consequences by requiring thorough technical reviews before modifications are implemented. It is a core component of OSHA’s Process Safety Management (PSM) and widely recognized in international safety frameworks.
During Operation and Beyond
Even after a process or facility has been commissioned, risk assessments remain an ongoing necessity to ensure continued safe operation and regulatory compliance. Over time, factors such as equipment degradation, procedural drift, and evolving external regulations can introduce new hazards or alter existing risks.
To address these dynamic conditions, periodic risk assessments are required, with specific activities including the revalidation of Process Hazard Analyses (PHA). Under OSHA’s Process Safety Management standard (29 CFR 1910.119), covered processes must undergo PHA revalidation at least every five years to ensure that hazard analyses remain current and reflect any changes in the process, equipment, or regulatory landscape. This continual cycle of assessment and revalidation is essential for proactively identifying and managing risks, maintaining process integrity, and upholding a strong safety culture throughout the operational life of the facility.
- Incident Investigation Reviews: Post-incident analyses inform future PHAs, particularly when new failure mechanisms or organizational gaps are uncovered.
- Audit and Inspection Feedback: Internal or third-party audits highlight gaps in compliance or procedure, which may trigger focused reassessments.
Routine assessments help maintain process safety effectiveness while supporting audit readiness and regulatory documentation.
Risk assessments are essential to the lifecycle of any process facility. Each assessment type—whether PRA, BOSS, HAZOP, LOPA, PSSR, or MoC—addresses different risk dimensions and is applied at a specific stage to maintain control over safety performance. Beyond preventing incidents, these assessments offer traceability, support design verification, and provide evidence of due diligence.
The most successful organizations recognize that risk assessments are more than technical exercises or regulatory requirements—they are cultural tools that foster communication across disciplines and embed safety thinking into everyday decisions. When executed properly, these assessments create a shared understanding of process risks and collective responsibility for their management.
Through a structured, phased approach to hazard identification and risk management, organizations can achieve safer project outcomes, improve operational reliability, and maintain alignment with regulatory and industry standards. Most importantly, they build the foundation for an operation where safety becomes not just a priority, but a core value that permeates all aspects of process management.
