This article discusses methods to conduct inherent safety reviews at key stages of the life cycle: during product and process development, during conceptual facilities planning early in the process design phase, and during routine operation.
More companies are building inherently safer design principles into their process safety management systems. This can be accomplished by incorporating inherently safer design methods into existing safety and process hazards reviews. Companies may wish to augment their existing review systems with inherent safety reviews at key points of the process life cycle.
Inherent safety review methods should be considered during appropriate stages of a typical project's life cycle. Suggested timing includes:
- During the chemistry forming (synthesis) stage for product/ process research and development to focus on the chemistry and process.
- During the facilities design scoping and development prior to completion of the design basis to focus on equipment and configuration.
- During regular operations to identify potential improvements for the next plant. Process improvement studies can then demonstrate the feasibility of inherent safety improvements so they can easily be incorporated into the design of the next plant or in major revamps of existing facilities.
Good preparation is very important for an effective inherent safety review. Preparation for the review is summarized as following:
- Define the desired product.
- Describe optional routes to manufacture the desired product (if available)
- Prepare simplified process flow diagram: Include alternative processes.
- Define chemical reactions: Desired and undesired; Determine potential for runaway reactions/decompositions.
- List all chemicals and materials employed: Develop a chemical compatibility matrix; Include air, water, rust, etc.
- Define physical, chemical, and toxic properties: Provide NFPA hazard ratings or equivalent.
- Define process conditions (pressure, temperature, etc.).
- Estimate quantities used in each process system (tanks, reactors, etc.): State plant capacity basis: Estimate quantities of wastes/emissions.
- Define site specific issues such as environmental, regulatory, community, spacing, permitting, etc.
After the background information is developed, the inherent safety review can be arranged. The review steps are recommended as follow:
- Define major potential hazards.
- Systematically review the process flow schematic looking at each process step and hazardous material to identify creative ways to improve the process by applying inherent safety principles to reduce or eliminate hazards.
- During the inherent safety review, at the design development stage, identify potential human factors/ergonomics issues that should be addressed by the design team.
During the systematic review methods of the process flow schematic, the team needs to examine some of the following questions:
- Can safer chemicals be used (nontoxic or nonvolatile reactant)?
- Can quantities be reduced (careful look at intermediates storage)?
- Can potential releases be reduced via lower temperatures or pressures, elimination of equipment or by using seal-less pumps?
- Can waste be reduced (regenerable catalyst or recycle)?
- What additional information is required (toxicology information or reactive chemicals data)?
- Can the equipment or process be simplified, be made mistake proof, or at least mistake tolerant, by applying ergonomic/human factors principles?
- Have trace materials or contaminants been identified along with their effects in the process?
In the typical operations review, the team identifies inherent safety opportunities for the next major expansion or grass roots facility such as:
- In the "chemistry forming" inherent safety review, the team will cover such things as:
- Understanding of the hazards
- Choice of best route to produce a given chemical or product
- Process improvement: Reactor types and conditions; Intermediate storage optimization; Waste minimization
- Requirements for additional information
- During design scoping, the team needs to concentrate on minimizing equipment, reducing inventories, simplifying the process, reducing wastes, and optimizing process conditions.
- During process hazards reviews (such as HAZOP/HAZID), inherent safety methods are also considered. Mistake proofing the design should receive attention and each safety critical device (last line of defense) and safety critical procedure should be examined to see if there is a way to eliminate the need for the device or procedure.