Process Hazard Analysis (PHA) is a structured review used to identify hazards in a process, estimate their likelihood and severity, and decide on safeguards. Teams examine scenarios, equipment, operating conditions and human actions, then record recommendations. In cyber-informed work, PHA should include digital dependencies, unsafe failure modes and the impact of loss or corruption of control signals.
How PHA turns a process into a hazard picture
PHA works by breaking a process into credible scenarios and asking what can fail, how it could fail, and what the result would be. That means looking at equipment, operating states, maintenance activities, alarms, interlocks, human actions, and abnormal conditions together, rather than treating them as separate issues. The output is a ranked set of hazards with recommended safeguards and follow-up actions.
For cyber-informed reviews, the process view should extend to control systems, sensors, actuators, logic, remote access paths, and dependencies that can distort or delay control decisions. The point is not just whether a component is secure, but whether loss of integrity, loss of availability, or incorrect control behavior changes the hazard profile of the process itself.
What a good PHA team actually examines
A strong PHA does not stop at a generic checklist. It tests deviations from intended operation, asks what happens if a control loop lies, a setpoint is wrong, a signal is delayed, or an operator is given misleading information. It also considers startup, shutdown, cleaning, bypasses, temporary workarounds, and maintenance windows because many serious hazards emerge outside steady-state operation.
The team usually combines process knowledge, operations experience, maintenance insight, and safety judgment so that each scenario is grounded in how the system really behaves. The method is deliberately structured because unstructured discussion tends to miss low-frequency, high-consequence combinations that only become obvious when the scenario is written out step by step.
- Identify the node, function, or operating segment being reviewed.
- Define credible deviations from normal operation.
- Trace causes across equipment, procedures, people, and digital controls.
- Estimate consequence and likelihood using the best available operational evidence.
- Record safeguards, action owners, and deadlines for recommendations.
Why the digital layer belongs in the hazard review
PHA becomes materially stronger when it includes the digital dependencies that shape process safety, such as controllers, historian feeds, alarm management, engineering workstations, remote support links, and instrumented shutdown logic. If those dependencies fail, are misconfigured, or are manipulated, the process may move into an unsafe state even when the physical equipment appears intact.
That is why cyber-informed engineering increasingly treats integrity of control signals as part of the hazard analysis itself. If a sensor is spoofed, a command is delayed, or an alarm is suppressed, the hazard is not merely “cyber” in the abstract, it becomes a process deviation with safety consequences. NHIMG’s OT Security Guide is a useful companion for understanding how industrial network design, segmentation, and control dependencies shape those scenarios.
Risk and Threat Considerations
PHA can fail when teams overfocus on equipment faults and underweight cyber-physical failure modes, especially where control logic, remote access, or shared engineering tools can affect many assets at once. In that case, the organization may believe a safeguard exists when the real dependency is a digital trust path that has not been validated under failure conditions.
Failure mechanism: Loss of signal integrity, unauthorized change, or delayed control action can defeat alarms, overrides, or shutdown logic, letting a process remain in an unsafe state longer than assumed.
Impact: The consequence can be incorrect operating decisions, escalation of an abnormal event, missed intervention windows, or a higher-severity incident than the physical design alone would suggest.
Standards & Framework Alignment
This section maps relevant standards and security frameworks to the operational risks and controls described in this guidance.
OWASP API Security Top 10 addresses the attack and risk surface, while CIS Controls v8, NIST SP 800-53 Rev 5 and NIST CSF 2.0 set the governance and control requirements practitioners need to meet.
| Framework | Control / Reference | Relevance |
|---|---|---|
| CIS Controls v8 | CIS-4 — Secure Configuration of Enterprise Assets and Software | PHA must account for unsafe control and software configurations in process environments. |
| Recommendation — Baseline and monitor configurations for control systems and supporting software. | ||
| NIST SP 800-53 Rev 5 | SA-15 — Development Process, Standards, and Tools | PHA in cyber-informed work depends on disciplined system and control engineering practices. |
| Recommendation — Apply engineering standards that preserve safety and security requirements across the lifecycle. | ||
| NIST CSF 2.0 | ID.RA-01 — Asset Vulnerabilities Are Identified and Documented | PHA is fundamentally a structured identification of hazards and weak points in a process. |
| PR.IR-01 — Networks and Environment Are Protected | PHA should include process-network dependencies and the effect of losing trust in control paths. | |
| Recommendation — Document process vulnerabilities and feed them into hazard and risk treatment decisions. Protect the process environment so control and safety functions remain trustworthy. | ||
| OWASP API Security Top 10 | API8 — Security Misconfiguration | Digital control interfaces and services can create unsafe process states when misconfigured. |
| Recommendation — Harden exposed control interfaces and validate configuration dependencies before operation. | ||
Practitioner Guidance
What to verify: Treat every safeguard recommendation as incomplete until you can show the dependency that makes it effective. If a safeguard depends on software logic, remote connectivity, or a data path, verify that those elements are included in the scenario and that failure of the digital layer does not invalidate the safeguard.
Decision rule: If a control signal, alarm, or interlock could be wrong, delayed, or unavailable, assess that condition as a primary hazard path, not a side note. Prioritise the scenarios that combine process upset with loss of trustworthy control information, because those are the ones most likely to change consequence severity.
Practitioner takeaway: The best PHA is not just a catalog of equipment failures, it is a structured test of whether the process still behaves safely when the human, physical, and digital layers do not all tell the truth at the same time.