Stages of Hazard Study of Process Plants

For a new project, the greatest benefit is obtained by carrying out several studies throughout the design process. One such sequence is the Hazard Study (HS) methodology developed by ICI which used six stages. Each study verifies that the actions of previous studies have been carried out and signed off and that the hazard and environmental issues have been identified and are being addressed in a timely and detailed manner.

The hazard study technique developed by ICI was very comprehensive and applied at different stages of the project life cycle to identify the hazards before the plant was commissioned and started‐up. The reports produced for each stage were very descriptive and in-depth as compared to the checklist and guideword approach which is practised widely in the industry today.

There is a need to revisit the original 6‐stage hazard study methodology developed by ICI more than four decades ago and to ensure that nothing important is being missed out in the way hazard studies are carried out at the present day.

Stage 1: Concept Stage Hazrad Review (HS 1)

This study is performed at the early design stage of the project. It is important at this early stage to apply the principles of inherent HSE within the design. This aims to eliminate, avoid, or reduce potential hazards in the process at the early stages of design as it is easy to modify the design.

In this first study, the basic hazards of the materials and the operation are identified.
It identifies what information is needed and the program of studies required to ensure that all SHE issues are adequately addressed.
The aspects covered may include reaction kinetics, toxicity data, environmental impact, and any special process features that need further evaluation.
A decision may be taken on which of the remaining hazard studies (two to six) should also be undertaken.
Review previous incidents on a similar plant
Review the application of inherent HSE
Consider the interaction of the project or plant with site activities
Review constraints due to national legislation
Set criteria for Safety, Health and Environmental aspects

Stage 2: HAZID at Front End Engineering Design of Project Definition Stage ( HS 2)

This study typically covers hazard identification and risk assessment, operability and control features that must be built into the detailed design and any special environmental features to be covered. At this stage, the design is still flexible and simple design changes may be applied. When the Process Flow Diagrams and basic information are available then with the help of Guide Diagrams;

Identify significant hazards in the process
Review possible mechanisms for the loss of containment
Eliminate hazards by changing the design where possible
Specify protective measures to meet the relevant criteria

Stage 3: Detailed Design Hazard Study (HS 3)

This normally involves a detailed review of a firm design aimed at the identification of hazard and operability problems. HAZOP studies are normally carried out at this stage and is widely used today. Hazard Study 3 is best carried out when firm Engineering Line Diagrams with outline operating, commissioning, maintenance and test procedures are available. The main objective is to review the final design and/or method with the help of guidewords e.g. No Flow, More Flow, Reverse Flow to:

Identify any hazards which could arise due to deviations from design intent
Define the consequences of such hazard and initiate appropriate actions
Examine control, operability (e.g. S/U, S/D) protective systems and maintenance (e.g. testing, repair) problems with due regard to transients, exposure to chemicals, ergonomics etc.

Stage 4: Construction / Design Verification Hazards Study (HS 4)

This review is performed at the end of the construction stage. The hardware is checked to ensure it has been built as intended and that there are no violations of the designer’s intent. It also confirms that the actions from the detailed design hazard study are incorporated, and operating and emergency procedures are checked.

Stage 5: Pre-Commissioning Safety Review (HS 5)

This examines the preparedness of the operations group for start-up. It typically covers training, the final operating procedures, preparation procedures, and readiness for start-up including function testing, cleanliness, and purging. Confirmation of compliance with company and legislative standards is done at this stage, for example, under the Pre Start-up Safety Review (PSSR) required under the OSHA PSM legislation in the USA.

Stage 6: Project Close-Out or Post-Startup Safety Review (HS 6)

This study is carried out a few months into the production phase, confirms that all outstanding issues from the previous five studies are complete and seeks any lessons that might give useful feedback to future design work.