When it adds most value
It is particularly useful when defining installations, processes, equipment or major changes. It allows comparison of layout, material, access and operating alternatives before every solution is finalised.
The NASA hazard analysis handbook places preliminary analysis in early phases, with subsequent updates. It is an engineering-method reference, not a universal obligation applying to every company.
Define scope and available information
Describe what is intended, where the system begins and ends, who interacts with it and which conditions are expected throughout its life. Interfaces, non-routine situations and foreseeable changes must be included.
Where data are still missing, the analysis must say so. An assumption about capacity, materials or staffing cannot silently become a fact. Recording those uncertainties allows them to be checked as the project develops.
How it relates to HAZID
HAZID refers to hazard identification and is often used for structured sessions involving people from different disciplines. The UK Building Safety Regulator’s guidance describes its usefulness in exploring scenarios and causes with a team familiar with the system.
PHA and HAZID are not names for a single mandatory template. A HAZID session can inform preliminary analysis through relevant questions and checklists; its format should suit the project’s objective and complexity.
What the review should produce
A useful record connects the hazard, scenario, possible causes, consequences and exposed people. Add planned controls, outstanding information, responsibilities and decisions needed before moving to another phase.
If a priority classification is used, its criteria must be explicit. The result should not be limited to a colour-coded list: every significant issue needs an identifiable decision, design measure or subsequent study.
Distinguish it from other analyses
A job safety analysis breaks down a task to examine safe execution. A HAZOP examines deviations in a more fully defined system. PHA takes place earlier with less mature information, without replacing the checks required later.
Nor does it, by itself, demonstrate legal conformity, reliability of safety functions or adequacy of occupational hygiene measures. It should identify which specific assessment must resolve each issue beyond its scope.
Maintain project traceability
In Spain, Article 15 of the Occupational Risk Prevention Act requires integrating prevention and combating risks at source. The Prevention Services Regulation requires assessment procedures that provide confidence in the result.
PHA can support that work, but must remain connected to the actual design. Changing an alternative requires reviewing its associated risks and checking that agreed measures are effectively incorporated.
Hypothetical example: a new loading area
Before fixing a loading-area layout, a team reviews traffic, maintenance access and interaction with pedestrians. It identifies that one alternative concentrates crossings at the point with the poorest visibility.
The design is modified and specific equipment and traffic checks remain outstanding. PHA prevents a poor decision from becoming established, without presenting itself as the final assessment of the future workplace.
