Checklist Analysis

A checklist analysis uses a list of possible problems, hazards, or procedural steps to be reviewed and verified. The analysis reminds the reviewers to consider specific issues to decide if they are addressed appropriately.

The checklist review is most suitable during the conceptual design, pilot plant, detailed engineering, construction and startup, routine operation, process modification or plant expansion, and decommissioning stages of a plant life cycle, as shown in Table 11-3. However, the checklist analysis is best applied in the preliminary stages of hazard identification; it should not be used as a replacement for a more detailed hazards identification/evaluation method.

The checklist used varies widely in detail and may include hundreds or even thousands of items. Checklist analysis can be used to evaluate materials, equipment, or procedures. Checklists can be customized for specific processes, specific types of process equipment (e.g., heat exchangers, pumps, distillation columns), and different stages in the lifetime of a plant.

A typical checklist is shown in Figure 11-2. This checklist has three checkoff columns. The first column is used to indicate those areas that have been thoroughly investigated. The second column is used for those items that do not apply to the particular plant. The last column is used to mark those areas requiring further investigation. Extensive notes on individual areas are kept separate from the checklist.

Checklist analysis includes three steps:²

²AICHE Center for Chemical Process Safety. Guidelines for Hazard Evaluation Procedures, 3rd ed. (Hoboken, NJ: Wiley Interscience, 2008).

1. Select and develop an appropriate checklist. Experienced team members start with available checklists, such as Figure 11-2. These checklists are enhanced with industrially available checklists. Available checklists from previous or other studies can be updated to include the latest codes, standards, regulations, and practices. If an appropriate checklist cannot be identified, one can be developed using the experience of the team.

2. Perform the checklist analysis. The review is conducted using plant tours, interviews, and document reviews. During these activities, the analysts compare the process equipment and operations to the checklist items. The recognized deficiencies are discussed by the team to develop recommendations.

3. Document the results. The final report includes the checklists used in the review, the noted deficiencies, recommendations, and justifications.

Checklist analysis can also be used to enhance other hazard evaluation methods, such as the what-if method.

Safety Reviews

The safety review was perhaps the earliest hazard evaluation method. It can be used for laboratory, pilot plant, and large process scale equipment. It can be used for new processes, substantial changes in existing processes, and processes that have not been reviewed recently. The success of the safety review strongly depends on the expertise of a safety review committee.

Safety reviews are typically performed during the following phases in a plant’s lifetime (see Table 11-3): construction/startup, routine operation, process modification or plant expansion, and decommissioning. They have the following purposes:

• Identify and alert operating personnel to the presence of process hazards

• Review operating procedures

• Identify equipment or process changes that may have introduced new hazards

• Evaluate the design basis of control systems, instrumented protective systems, and emergency relief systems

• Review the application of new technology to existing hazards

• Review the adequacy of maintenance and safety systems²

Often a safety review will identify the need for a more detailed review, such as other methods described in the scenario-based methods shown in Table 11-1.

After startup, safety reviews should be conducted on a periodic basis or whenever changes are made to the process, procedures are modified, a “near miss” occurs, or if leading or lagging indicators reveal a deficiency.

The safety review process includes the following steps:³

³AICHE Center for Chemical Process Safety. Guidelines for Hazard Evaluation Procedures, 3rd ed. (Hoboken, NJ: Wiley Interscience, 2008).

1. Prepare for the review. A team is formed and given the responsibility for the review. The review team should include operators, maintenance workers, process engineers, and instrument specialists. Other specialists should be available for answering specific technical questions. One or more of the team members are assigned the responsibility to gather relevant information, including sketches; process flow diagrams (PFDs); process and instrument diagrams (P&IDs); equipment specifications; process chemicals and their hazardous properties; codes, standards, and procedures for operation; maintenance; emergency procedures; and other available information. Recommendations from previous safety reviews are also obtained, if available.

2. Make additional preparations and perform the review. Team members are assigned to tour the facility; interview people with detailed knowledge of the chemistry, engineering requirements, plant controls, and equipment (including reaching out to other sites and companies); review inspection results and the status of previous safety review recommendations; review incident investigation reports and the status of recommendations; and gather and evaluate other relevant and available information. When this is completed, the team meets to review these results. This meeting is used to identify hazards, evaluate the outcomes, and decide how the hazards are addressed.

3. Document the results. After the review, the team develops a report and recommendations with appropriate justifications. Prior to publication, the recommendations are reviewed with management. The final approved recommendations are included in the final safety review document.

Inherent Safety Reviews

Inherent safety was discussed in Section 1-13. Inherent safety reviews evaluate the plant to identify ways to prevent incidents by eliminating or reducing hazards rather than by adding more control systems, interlocks, redundancy, and special operating procedures.

Inherent safety reviews, as shown in Table 11-3, are most suitable during research and development, conceptual design, detailed engineering, routine operation, and process modification or plant expansion stages of a process lifetime.

The steps in an inherent safety review are as follows:

1. Collect and review available information.

2. Define the major hazards.

3. Systematically review the process at each process step to identify hazards and to determine creative ways to improve the process by applying principles of inherently safer design.

4. Document the review and follow-up actions.

Inherent safety reviews can be included with other PHA methods or part of a much larger hazard evaluation.

Preliminary Hazard Analysis

A preliminary hazard analysis (not to be confused with the acronym PHA used for process hazard analysis) focuses in a general way on the hazardous materials and major process areas in the plant. It formulates a list of hazards and incident scenarios by considering various process characteristics. It can also identify alternative design criteria that could eliminate or reduce the hazards. It is specifically intended to discover hazards early in the plant’s life, so information may be limited. The review team must, at least, have a written general description of the conceptual design, some chemistry and reactions, and major equipment.

Preliminary hazard analysis is suitable for the research and development, conceptual design, pilot plant, detailed engineering, and process modification or plant expansion of a process lifetime, as shown in Table 11-3. It includes the following steps:

1. Prepare for the review. Form the team, drawing on available experience from many sources. Gather available information about the process, including information and operating experience from a similar plant.

2. Perform the review. Consider hazardous materials and plant equipment (e.g., fuels, reactive chemicals, high-pressure systems); safety-related interfaces between the plant equipment and materials (human error); environmental factors (e.g., earthquakes, floods); operating, testing, maintenance, and emergency procedures; facility support; and safety-related equipment.

3. Document the results. The resulting preliminary hazard analysis worksheet has the following columns:

   1. Hazards identified

   2. Initiating causes (e.g., mechanical failure, procedural error, external force, raw material variation, or environmental condition)

   3. Major effects or consequences (e.g., potential for injuries or fatalities)

   4. Hazard category or a priority using the following scale: Hazard Category I (negligible), Hazard Category II (marginal), Hazard Category III (critical), and Category IV (catastrophic)

   5. Corrective/preventive measures, such as the application of inherently safety design (eliminate or reduce hazards); safeguards, both preventive and mitigative

Relative Ranking

Relative ranking methods calculate a number or index that is indicative of the hazards in the process. They are excellent choices for comparing various process alternatives or deciding if a more rigorous PHA method is required. These methods are most suitable during the research and development, conceptual design, and process modification or plant expansion phases of a process lifetime, as shown in Table 11-3.

The most popular relative ranking methods are the Dow Fire and Explosion Index (F&EI) and the Dow Chemical Exposure Index (CEI). Both of these approaches use formal systematized approaches based on a rating form, similar to an income tax form. The final number provides a relative ranking of the hazard.

The F&EI is designed for rating the relative hazards with the storage, handling, and processing of flammable materials. The procedure begins with a material factor, which is a function only of the chemical. The material factor is first adjusted for general and special process hazards—for example, storage above the flash or boiling point, endothermic or exothermic reactions, and fired heaters. Credits for various safety systems and procedures are then applied for estimating the consequences of the hazard. The F&EI is also capable of estimating a dollar value for property damage.

The CEI is a relative ranking method for rating the acute health hazard potential for people in neighboring communities or plants arising from possible chemical release. The procedure begins with identification of possible release incidents, such as releases from pipes and hoses; pressure relief devices relieving directly to the atmosphere; releases from vessels; and tank overflows and spills. The incidents are used with a number of simplified source models provided in the CEI guide to estimate the release rate of material. The Emergency Response Planning Guidelines (ERPG) are then used with a simplified dispersion model to determine the CEI value and downwind hazard distances resulting from the release.

The sum of both the F&EI and CEI numbers for a specific process can be used to decide if a more rigorous PHA method is required.

Example 11-1

Consider the laboratory reactor system shown in Figure 11-3. This system is designed to react phosgene (COCl₂) with aniline to produce isocyanate and HCl. The reaction is shown in Figure 11-4. The isocyanate product is used for the production of foams and plastics.

Phosgene is a colorless vapor with a normal boiling point of 46.8°F. Thus, it is usually stored as a liquid in a container under pressure above its normal boiling point temperature. The TLV-TWA for phosgene is 0.1 ppm, and its odor threshold is 0.55 ppm, well above the TLV-TWA.

Aniline is a liquid with a boiling point of 364°F. Its TLV-TWA is 2 ppm. It is absorbed through the skin.

In the process shown in Figure 11-3, phosgene is fed from the supply container through a valve into a fritted glass bubbler in the reactor. The reflux condenser condenses the aniline vapors and returns liquid aniline to the reactor. A caustic scrubber is used to remove the phosgene and HCl vapors from the exit vent stream. The complete process is contained in a hood.

Conduct a safety review of this process.

Solution

The safety review was completed by two individuals—the process is simple and small enough that a full committee review is not necessary. The final process design is shown in Figure 11-5. The changes and additions to the process are as follows:

1. A flow indicator provides a visual indication of the flow. This is a simple bubbler.

2. A relief system composed of a glass U-tube filled with liquid is added with an outlet to the scrubber. This prevents pressure hazards resulting from a possibly plugged fritted glass bubbler. This relief will operate at a few inches of water gauge pressure.

3. The trap catches any liquid phosgene that may come from the tank.

4. The existing scrubber is not very effective at absorbing vapors from a single open tube. This is replaced by two bubblers with caustic and ammonium hydroxide to absorb any phosgene or HCl vapor.

5. Vacuum is added to reduce the boiling point temperature.

6. A pail of caustic is added (the phosgene cylinder would be dumped into this pail in the event of a cylinder or valve leak; the caustic would absorb the phosgene).

In addition, the reviewers made the following recommendations: (1) Hang phosgene indicator paper around the hood, room, and operating areas (this paper is normally white but turns brown when exposed to 0.1 ppm of phosgene); (2) develop and use a safety checklist daily, before the process is started; and (3) post an up-to-date process sketch near the process.

Hazard and Operability Studies

The objective of a HAZOP is to systematically identify and evaluate scenario-based hazards in a chemical plant and to identify operability problems that could impact plant productivity. This method results in recommendations to reduce the risk. The basic idea is to let the mind go free in a controlled fashion so as to consider all the possible ways that plant and operational failures might occur. The HAZOP method is suitable for the pilot plant, detailed engineering, routine operation, process modification or plant expansion, and incident investigation stages of a process lifetime, as shown in Table 11-3.

Before the HAZOP study is started, detailed information on the process must be gathered. This includes up-to-date process flow diagrams (PFDs), piping and instrumentation diagrams (P&IDs), detailed equipment specifications, materials of construction, a list of all chemicals and process materials including safety data sheets (SDSs), and mass and energy balances, to name a few. Other information may be important depending on the process. All information must be current and reliable.

The full HAZOP study requires a committee composed of personnel from the plant, laboratory, engineering, maintenance, instrument, and safety departments, to name a few. One individual must be a trained HAZOP leader and serves as the committee chair. This person leads the discussion and must be experienced with both the HAZOP procedure and the chemical process under review. One individual must also be assigned the task of recording the results; a number of vendors provide software to assist with this function.

The committee meets on a regular basis for a few hours at a time. The meeting duration must be short enough to ensure continuing interest and input from all committee members. A large process might take several months of twice-weekly meetings to complete the HAZOP study. Obviously, a complete HAZOP study requires a large investment in time and effort, but the result is worth the effort. Definitions for HAZOP study terms are shown in Table 11-5.

Table 11-5 Definitions for HAZOP Study Terms

Source: Adapted from AICHE CCPS Faculty Workshop. “Hazard Identification and Evaluation.” (Freeport, TX: Dow Chemical Company, June 2017).

The HAZOP procedure uses the following steps to complete an analysis:

1. Begin with a detailed flow sheet. Divide the flow sheet into a number of process units. Thus, the reactor area might be one unit, and the storage tank area another. Select a unit for study.

2. Choose a study node, such as vessel, line, or operating instruction. HAZOPs are also used for procedures, especially when human factors may be important—including procedures such as startup, shutdown, emergency operations, and sampling.

3. Describe the design intent of the study node. For example, vessel V-1 is designed to store the benzene feedstock and provides it on demand to the reactor.

4. Pick a process parameter: flow, level, temperature, pressure, concentration, pH, viscosity, state (solid, liquid, or gas), agitation, volume, reaction, sample, component, start, stop, stability, power, or inert. Other process parameters might be valid for your particular process.

5. Apply a guide word to the process parameter to suggest possible deviations. Table 11-6 lists some guide words. Note that some of the guide word process parameter combinations are meaningless, as shown in Table 11-7 for process lines and in Table 11-8 for vessels. Guidelines, associated parameters, and deviations are listed in Table 11-9.

Table 11-6 Guide Words Used for the HAZOP Procedure

Table 11-7 Valid Guide Word and Process Parameter Combinations for Process Lines

Note: x’s represent valid combinations.

Table 11-8 Valid Guide Word and Process Parameter Combinations for Process Vessels

Note: x’s represent valid combinations.

Table 11-9 HAZOP Deviations for Different Guidewords and Parameters

6. If the deviation is applicable, determine possible causes and note any protective systems.

7. Evaluate the consequences of the deviation (if any).

8. Recommend action (what? by whom? by when?).

9. Record all information.

10. Repeat steps 5 through 9 until all applicable guide words have been applied to the chosen process parameter.

11. Repeat steps 4 through 10 until all applicable process parameters have been considered for the given study node.

12. Repeat steps 2 through 11 until all study nodes have been considered for the given section and proceed to the next section on the flow sheet.

Since the HAZOP method is scenario based, multiple scenarios are defined in steps 1 through 7, and the recommendations are developed in step 8.

Note that there are 18 process parameters listed and 10 guide words, so that 180 total combinations are possible for each study node. Thus, the HAZOP procedure produces a huge amount of combinations to consider.

The guide words AS WELL AS, PART OF, and OTHER THAN can sometimes be conceptually difficult to apply. AS WELL AS means that something else happens in addition to the intended design intention. This could be boiling of a liquid, transfer of some additional component, or transfer of some fluid somewhere else than expected. PART OF means that one of the components is missing or the stream is being preferentially pumped to only part of the process. OTHER THAN applies to situations in which a material is substituted for the expected material, is transferred somewhere else, or solidifies and cannot be transported. The guide words SOONER THAN, LATER THAN, and WHERE ELSE are applicable to batch processing.

An important part of the HAZOP procedure is the process required to record and use the results. Many methods can be used to accomplish this, and most companies customize their approach to fit their way of doing things.

Table 11-10 presents one type of basic HAZOP form. The first column, denoted “Item,” is used to provide a unique identifier for each case considered. The numbering system used comprises a number–letter combination. Thus, the designation “1A” indicates the first study node and the first guide word. The second column lists the study node considered. The third column lists the process parameter, and the fourth column lists the deviations or guide words. The next three columns are the most important results of the analysis. The first column lists the possible causes, which are determined by the committee and are based on the specific deviation guide word combination. The next column lists the possible consequences of the deviation. The next column lists the safeguards that currently exist. The final column lists the action required to prevent the hazard from resulting in an incident. Notice that the items listed in these four columns are numbered consecutively. Additional columns can be added to track the work responsibility and the completion of the work.

Example 11-2

Consider the reactor system shown in Figure 11-6. The reaction is exothermic, so a cooling system is used to remove the excess energy of reaction (this is the design intent). In the event that the cooling function is lost, the temperature of the reactor would increase. This would lead to an increase in reaction rate, resulting in additional energy release. The ultimate result would be a runaway reaction with pressures exceeding the bursting pressure of the reactor vessel.

The temperature within the reactor is measured and is used to control the cooling water flow rate with a valve. Perform a partial HAZOP study on this unit to improve the safety of the process. Use the cooling coil as a study node, a process parameter of flow, and the guide words of NO, HIGH, and LOW.

Solution

The guide words are applied to the study node of the cooling coils with the process parameter of flow. The HAZOP results are shown in Table 11-10 (though the table does not contain the complete results of the HAZOP study).

Table 11-10 HAZOP Study Applied to the Exothermic Reactor of Example 11-2

Project name: Example 11-4					Date: July 18, 2019		Page 1 of 2
Process: Reactor of Example 11-4
Section: Reactor shown in example 11-2					Reference drawing:
Item	Study node	Process parameters	Deviations (Guide words)	Possible causes	Possible consequences	Existing safeguards	Action required
1A	Cooling coils	Flow	No	1. Control valve fails closed	1. Loss of cooling, possible runaway.	1 & 2. Flow transmitter with low-flow alarm and high-temperature alarm on reactor.	1. Select valve to fail open.
				2. Plugged cooling coils	2. Same as 1.		2. Install filter with maintenance procedure. Install cooling water flow meter and low-flow alarm. Install high-temperature alarm to alert operator.
				3. Cooling water service failure.	3. Same as 1.	3, 4, 5. No safeguards.	3. Check and monitor reliability of water service.
				4. Controller fails and closes valve.	4. Same as 1.		4. Place controller on critical instrumentation list.
				5. Air pressure fails, closing valve.	5. Same as 1.		5. See 1A.1.
1B			High	1. Control valve fails open.	1. Reactor cools, reactant concentration builds, possible sleeping reactor.	1. No safeguards.	1. Instruct operators and update procedures.
				2. Controller fails and opens valve.	2. Same as 1.	2. Flow transmitter with high-flow alarm.	1. Place controller on critical instrumentation list. See 1A.4
1C			Low	1. Partially plugged cooling coils.	1. Diminished cooling, possible runaway.	1. See 1A.1	1. See 1A.2
				2. Partial water source failure.	2. Same as 1.	2. See 1A.1	2. See 1A.2
				3. Control valve fails to respond.	3. Same as 1.	3. No safeguard.	3. Place valve on critical instrumentation list.

Some of the process modifications resulting from the more detailed study are as follows:

• Select the control valve to fail open.

• Install a filter to prevent plugging of the cooling coils. Add the filter to the maintenance schedule.

• Install a cooling water flow meter and a low-flow alarm (which will provide an immediate indication of cooling loss).

• Install redundant temperature indicators and controllers, and include equipment from different vendors to prevent common-cause failures.

• Install a high-temperature alarm to alert the operator in the event of cooling loss.

• Install a high-temperature shutdown system. This system would automatically shut down the process in the event of a high reactor temperature. The shutdown temperature would be higher than the alarm temperature to provide the operator with the opportunity to restore cooling before the reactor is shut down.

• Install a check valve in the cooling line to prevent reverse flow. A check valve could be installed before and after the reactor to prevent the reactor contents from flowing upstream and to prevent the backflow in the event of a leak in the coils.

• Periodically inspect the cooling coil to ensure its integrity.

• Study the cooling water source to consider possible contamination and interruption of supply.

• Consider redundant water and air sources. Nitrogen can be a backup for air and a storage tank of water would back up the water supply.

In the event that the cooling water system fails (regardless of the source of the failure), the high-temperature alarm and emergency shutdown system should prevent a runaway reaction. The review committee performing the HAZOP study decided that the installation of a backup controller and control valve was not necessary. The high-temperature alarm and shutdown system already prevent a runaway reaction in this event.

Similarly, a loss of coolant water source or a plugged cooling line would be detected by either the alarm or the emergency shutdown system. The review committee suggested that all coolant water failures be properly reported and that if a particular cause occurred repeatedly, then additional process modifications would be warranted.

A key advantage of the HAZOP approach is that it provides a more complete identification of the hazards, including information on how hazards can develop as a result of operating procedures and operational upsets in the process. Companies that perform detailed HAZOP studies find that their plants operate better and have less downtime, their product quality is improved, less waste is produced, and their employees are more confident in the safety of the process. The disadvantages are that the HAZOP approach is tedious to apply and requires considerable staff time and effort.

Failure Modes and Effects Analysis

FMEA was one of the first highly structured, systematic techniques for failure analysis. It was developed by reliability engineers in the late 1950s to minimize malfunctions of military systems. This method is used to identify how equipment can fail (or be improperly operated) and its effects on the process. Current safeguards to prevent these failures and the level of risk for each failure are also identified.

The benefits of FMEA include reduced failures by identification and elimination of potential failure modes. FMEA is most suitable for pilot plant, detailed engineering, routine operation, process modification or plant expansion, and incident investigation stages of a process lifetime,^5,6 as shown in Table 11-3.

⁵AICHE Center for Chemical Process Safety. Guidelines for Hazard Evaluation Procedures, 3rd ed. (Hoboken, NJ: Wiley Interscience, 2008), p. 134.

⁶R. McDermott, R. Mikulak, and M. Beauregard. The Basics of FMEA, 2nd ed. (London, UK: Taylor & Francis Group, 2009).

An FMEA study includes four steps:

1. Assemble a cross-functional team of three to six knowledgeable people, from functions such as design, research, operations, and maintenance. Select team members who really know and understand the details of the process.

2. Define the systems to be studied, including the boundaries and the appropriate level of resolution. A P&ID and other plant descriptions will assist with this step. If a plant-level hazard is being addressed, the FMEA should focus on the failure modes of individual systems and their effects. This could include the plant’s feed system, mixing system, separation systems, and support systems. When a system-level hazard is being addressed, the FMEA should focus on the failure modes of individual equipment and their effects on the overall system. This could include the feed pump, mixing motor, control valves, or temperature sensors. Maintenance records providing information on equipment failures and modes are very useful.

3. Conduct a deliberate and systematic review by using a worksheet like Table 11-11 for Example 11-3.

Identification: A unique identifier that relates to the P&ID, process, or location.

Equipment description: Include characteristics that may influence failure modes (e.g., the air-operated control valve to control cooling water flow fails open).

Failure modes: List all failure modes for each component (e.g., fails open, fails closed, leaks out, leaks internally).

Failure mode causes: Causes may include residue in line, loss of air or nitrogen, corrosion failures, and so on.

Effects: Include local effects and anticipated effects on other equipment or the system (e.g., temperature increases and pressure rises).

Existing safeguards: Existing safety features that decrease the likelihood or mitigate the consequences.

Actions/recommendations: Corrective actions may focus on effects or causes of effects (e.g., consider adding a high-pressure alarm and consider a shutdown system for high pressures). Actions would include new safeguards (preventive, mitigative), steps such as training, and more reliable controls to prevent common cause failures.

Risk level: A knowledgeable team can rate the risk level for each failure mode. This information is used later when deciding which actions should be taken. The risk level is assigned using a scale from 1 = low level to 10 = high level.

4. Document the results. After the FMEA worksheet is completed, the team evaluates the results and makes decisions to reduce the consequences or likelihood of each of the failure modes. The actions are prioritized based on the risk level.

What-If Analysis

The what-if method is a brainstorming method to ask questions or voice concerns about possible undesirable events. This method is suitable for the conceptual design, pilot plant, detailed engineering, construction and startup, routine operation, process modification or plant expansion, decommissioning, and incident investigation stages of a process lifetime, as shown in Table 11-3.

The purpose of the what-if analysis is to use what-if questions to facilitate discussions to (1) find abnormal situations, (2) identify existing safeguards that prevent and mitigate incidents, and (3) develop actions and recommendations to improve controls and safeguards to eliminate, contain, or minimize hazards. The success of this method strongly depends on the experience level of the review team.

This what-if method has three steps:

1. Gather information. Detailed P&IDs are acquired from engineering, and process details are obtained from plant personnel including written plant descriptions. Maintenance records on specific equipment are valuable. Additional information is acquired using tours, inspections, and interviews.

2. Conduct the review. The team first tours a section of the plant (e.g., the reactor) with the P&ID and develops what-if questions to facilitate discussions to develop improved controls and safeguards. The what-if question table could include, for example: What if the monomer feed valve fails open? What if control air fails off? What if valve A is plugged? What if agitation stops? What if the nitrogen feed valve fails closed? What if valve B fails open?

   The what-if analysis table contains six columns: What-If Questions, Hazards, Consequences, Existing Safeguards, Actions/Recommendations, and Levels of Risk. It is similar to Table 11-11.

   Actions/recommendations can also include corrective actions to reduce consequences (e.g., adding either a high-pressure alarm, a shutdown system for high pressures, additional training, using other hardware and/or replacing hardware with more reliable devices). In addition, they can include consideration of new safeguards (preventive or mitigative), more reliable controls, redundant controls, or controls from different vendors to prevent common cause failures.

3. Document the results. The documented results are developed after a thorough review of the what-if analysis table. The final results should include three tables: the two tables mentioned earlier (what-if questions table and what-if analysis table) and a results table with the prioritized actions using the level of risk developed by the team.

What-If/Checklist Analysis

What-if/checklist analysis is a hybrid method that combines a what-if analysis method with the checklist method. The idea is to combine the creative, brainstorming features of the what if analysis with the systematic features of the checklist method. The what-if/checklist analysis method is suitable for the conceptual design, pilot plant, detailed engineering, construction and startup, routine operations, process modification or plant expansion, and decommissioning stages of a process lifetime, as shown in Table 11-3.

The what-if/checklist analysis has four steps: (1) prepare for the review; (2) develop the tables described in the what-if analysis (including incident scenarios); (3) use the checklists to make sure all areas and issues are covered adequately; and (4) document the results (include tables with recommendations, the checklists, and a summary of results).

Suggested Reading

AICHE Center for Chemical Process Safety. Guidelines for Chemical Process Quantitative Risk Analysis, 2nd ed. (New York, NY: AICHE Center for Chemical Process Safety, 2000).

AICHE Center for Chemical Process Safety. Guidelines for Developing Quantitative Safety Risk Criteria (Hoboken, NY: Wiley Interscience, 2009).

AICHE Center for Chemical Process Safety. Guidelines for Risk-Based Process Safety (Hoboken, NY: Wiley Interscience, 2008).

S. Mannan, ed. Lees’ Loss Prevention in the Process Industries, 4th ed. (London, UK: Butterworth Heinemann, 2012).