We use the terms of tool and method interchangeably. Methods/tools include HAZOP of continuous mode, HAZOP of steps for non-continuous modes of operation, What-if, Checklist. The scope and goals establish the Qualitative Hazard Evaluation that you need to accomplish using one or more of these tools/methods. So, a Process Hazard Analysis (PHA) is a specific scope of qualitative risk evaluation that uses one or more tools/methods to accomplish the complete scope, if the tools/methods are applied correctly and thoroughly for the scope of work.
Example: For the PHA of a Refinery unit within the USA, the PHA will typically require the use of the “parametric deviation” HAZOP method for the evaluation of most equipment nodes to address continuous mode of operation and What-If method of some subsystems (where HAZOP would be overkill). Then we would use 2 guideword HAZOP of steps or What-If of an entire task, to evaluate the hazards of skipping steps or doing steps wrong during startup, shutdown, and online maintenance modes of operation; and use one of these same two methods for evaluation of loading and unloading (if applicable). Finally, we would use the Checklist method to make sure we thoroughly covered human factors, facility siting, and selected damage mechanisms (this augments the brainstorming results, which come from HAZOP and What-If). So, in this example, we use 3 methods (tools) and also variations on one method (HAZOP) to thoroughly meet the goals (scope and depth) of a PHA of a refinery unit. The deliverable is a PHA report; inside of the report are the scope, membership of team, description of methods used, why each method was chose, list of recommendations, analysis tables (worksheets) with cause, consequence, existing safeguards, and (if necessary) recommendations to reach tolerable risk as determined by the qualitative opinion of the PHA team; the style of the worksheets various slightly for each method.