Unit Operation Laboratories

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Process Safety Review Checklist

Note: Consider the check list in terms not only of steady-state operation, but also startup, shutdown, and upsets of all conceivable types.

Materials

1. What process materials are unstable or spontaneously ignitable?
2. What evaluation has been made of impact sensitivity?
3. Has an evaluation of possible uncontrolled reaction or decomposition been made?
4. What data are available on amount and rate of heat evolution during decomposition of any material in the process?
5. What precautions are necessary for flammable materials?
6. What flammable dust hazards exist?
7. What materials are highly toxic?
8. What has been done to assure that materials of construction are compatible with the chemical process materials that are involved?
9. What maintenance control is necessary to assure replacement of proper materials, e.g., to avoid excessive corrosion, to avoid producing hazardous compounds with reactants?
10. What changes have occurred in composition of raw materials and what resulting changes are in process?
11. What is done to assure sufficient control of raw material identification and quality?
12. What hazards can be created by failure of supply of one or more raw materials?
13. What assurance is there of adequate raw material supply?
14. What hazards can occur as a result of loss of gas for purging, blanketing, or inerting? How certain is gas supply?
15. What precautions need to be considered relative to stability of all materials in storage?
16. What fire extinguishing agents are compatible with process materials?
17. What fire emergency equipment and procedures are being provided?

Reactions

1. How are potentially hazardous reactions isolated?
2. What process variables could, or do, approach limiting conditions for hazard?
3. What unwanted hazardous reactions can be developed through unlikely flow or process conditions or through contamination?
4. What combustible mixtures can occur within equipment?
5. What precautions are taken for processes operating near or inside the flammable limits?
6. What are process margins of safety for all reactants and intermediates?
7. What reaction rate data are available on the normal, or abnormally possible, reactions?
8. How much heat must be removed for normal, or abnormally possible, exothermic reactions?
9. How thoroughly is chemistry of the process known? (See NFPA 93Manual of Hazardous Chemical Reactions94.)
10. What foreign materials can contaminate the process and create hazards?
11. What provision is made for rapid disposal of reactants if required by plant emergency?
12. What provisions are made for handling impending runaways and for short-stopping an existing runaway?
13. How fully is the chemistry of all desired and undesired reactions known?
14. What hazardous reactions could develop as a result of mechanical equipment (pump, agitator, etc.) failure?
15. What hazardous process conditions can result from gradual or sudden blockage in equipment?
16. What raw materials or process materials can be adversely affected by extreme weather conditions?
17. What process changes have been made since the previous process safety review?

Operations

1. When was the written operating procedure last reviewed and revised?
2. How are new operating personnel trained on initial operation and experienced operating personnel kept up-to-date on plant operating procedures, especially for startup, shutdown, upsets, and emergencies?
3. What plant revisions have been made since the last process safety review?
4. What special cleanup requirements are there before startup and how are these checked?
5. What emergency valves and switches cannot be reached readily? What procedures are there to cope with these situations?
6. What safety precautions are needed in loading liquids into, or withdrawing them from, tanks? Has the possibility of static electricity creation been adequately taken care of?
7. What process hazards are introduced by routine maintenance procedures?
8. What evaluation has been made of the hazards of sewered materials during normal and abnormal operation?
9. How dependable are supplies of inerting gas and how easily can supplies to individual units be interrupted?
10. What safety margins have been narrowed by revisions of design or construction in efforts to debottleneck operations, reduce cost, increase capacity, or improve quality?
11. What provisions does the operating manual have for coverage of startup, shutdown, upsets and emergencies?
12. What economic evaluation has dictated whether a batch process or a continuous one is used?

Equipment

1. In view of process changes since the last process safety review, how was adequate size of equipment assured?
2. Are any venting systems manifolded, and if so, what hazards can result?
3. What procedure is there for assuring adequate liquid level in liquid seals?
4. What is the potential for external fire which may create hazardous internal process conditions?
5. Is explosion suppression equipment needed to stop an explosion once started?
6. Where are flame arresters and detonation arresters needed?
7. In confined areas, how is open fired equipment protected from spills?
8. What safety control Is maintained over storage areas?
9. In the case of equipment made of glass or other fragile material, can a more durable material be used? If not, is the fragile material adequately protected to minimize breakage? What is the hazard resulting from breakage?
10. Are sight glasses on reactors provided only where positively needed? On pressure or toxic reactors, are special sight glasses provided which have a capability to withstand high pressure?
11. What emergency valves and switches cannot be reached readily?
12. When was pertinent equipment, especially process vessels, last checked for pressure rating?
13. What hazards are introduced by failure of agitators?
14. What plugging of lines can occur and what are the hazards?
15. What provisions are needed for complete drainage of equipment for safety in maintenance?
16. How was adequacy of ventilation determined?
17. What provisions have been made for dissipation of static electricity to avoid sparking?
18. What requirements are there for concrete bulkheads or barricades to isolate highly sensitive equipment and protect adjacent areas from disruption of operations?

Piping and Valves

1. Were piping systems analyzed for stresses and movement due to thermal expansion?
2. Are piping systems adequately supported and guided?
3. Are piping systems provided for anti-freezing protection, particularly cold water lines, instrument connections and lines in dead-end service such as piping at standby pumps?
4. Are provisions made for flushing out all piping during start-up?
5. Are cast iron valves avoided in strain piping?
6. Are non-rising stem valves being avoided?
7. Are double block and bleed valves used on emergency inter-connections where possible cross-contamination is undesirable?
8. Are controllers and control valves readily accessible for maintenance?
9. Are bypass valves readily reached for operation? Are they so arranged that opening of valves will not result in an unsafe condition?
10. Are any mechanical spray steam desuperheaters used?
11. Are all control valves reviewed for safe action in event of power or instrument air failure?
12. Are means provided for testing and maintaining primary elements of alarm and interlock instrumentation without shutting down processes?
13. What provisions for draining and trapping steam piping are provided?

Pressure and Vacuum Relief

1. What provisions is there for flame arresters on discharge of relief valves or rupture discs on pressurized vessels?
2. What provisions are there for removal, inspection, and replacement of relief valves and rupture discs, and what scheduling procedure?
3. What need is there for emergency relief devices: breather vents, relief valves, rupture discs, and liquid seals? What are the bases for sizing these?
4. Where rupture discs are used to prevent explosion damage, how are they sized relative to vessel capacity and design?
5. Where rupture discs have delivery lines to or from the discs, what has been done to assure adequate line size relative to desired relieving dynamics? To prevent whipping of discharge end of line?
6. Are discharges from vents, relief valves, rupture discs, and flares located to avoid hazard to equipment and personnel?
7. What equipment, operating under pressure, or capable of having internal pressures developed by process malfunction, is not protected by relief devices and why not?
8. Is discharge piping of relief valves independently supported? Make piping as short as possible and with minimum changes in direction.
9. Are drain connections provided in discharge piping of relief valves where condensate could collect?
10. Are relief valves provided on discharge side of positive displacement pumps; between positive displacement compressor and block valves; between back-pressure turbine exhaust flanges and block valves?
11. Where rupture discs are in series with relief valves to prevent corrosion on valve or leakage of toxic material, install rupture disc next to the vessel and monitor section of pipe between disc and relief valve with pressure gauge and pressure bleed-off line. Have any rupture discs been installed on discharge side of relief valve?
12. What provisions for keeping piping to relief valves and vacuum breakers at proper temperature to prevent accumulation of solids from interfering with action of safety device are provided?

Machinery

1. Are adequate piping supports and flexibility provided to keep forces on machinery due to thermal expansion of piping within acceptable limits?
2. What is separation of critical and operating speeds?
3. Are check valves adequate and fast acting to prevent reverse flow and reverse rotation of pumps, compressors and drivers?
4. Are adequate service factors on speed changing gears in shock service provided?
5. Are there full-flow filters in lube-oil systems serving aluminum bearings?
6. Are there provisions for draining and trapping steam turbine inlet and exhaust lines?
7. Are there separate visible-flow drain lines from all steam turbine drain points?
8. Are driven machines capable of withstanding tripping speed of turbine drain points?
9. Are non-lubricated construction or non-flammable synthetic lubricants used for air compressors with discharge pressures of greater than 75 psig to guard against explosion?
10. What provisions are made for emergency lubrication of critical machinery during operation and during emergency shutdowns?
11. Are provisions made for spare machines or critical spare parts for critical machines?
12. Are there provisions for operation or safe shutdown during power failures?
13. Are vibration switches on alarm or on interlock for cooling tower fans provided?

Instrumentation Control

1. What hazards will develop if all types of motive power used in instrumentation should fail nearly simultaneously?
2. If all instruments fail simultaneously, is the collective operation still fail -safe?
3. What provision is made for process safety when an instrument, instrumental in process safety as well as in process control, is taken out of service for maintenance? When such an instrument goes through a dead time period for standardization or when, for some other reason, the instrument reading is not available?
4. What has been done to minimize response time lag in instruments directly or indirectly significant to process safety? Is every significant instrument or control device backed up by an independent instrument or control operating in an entirely different manner? In critical processes, are these first two methods of control backed up by a third ultimate safety shutdown?
5. Has the process safety function of instrumentation been considered integrally with the process control function throughout plant design?
6. What are the effects of extremes of atmospheric humidity and temperature on instrumentation?
7. What gauges, meters, or recorders cannot be read easily? What modifications are being made to cope with or solve this problem?
8. Is the system completely free of sight glasses or direct reading liquid level gauges or other devices which, if broken, could allow escape of the materials in the system?
9. What is being done to verify that instrument packages are properly installed? Grounded? Proper design for the environment?
10. What procedures have been established for testing and proving instrument functions?
11. What periodic testing to check performance and potential malfunction is scheduled?

Malfunctions

1. What hazards are created by the loss of each feed, and by simultaneous loss of two or more feeds?
2. What hazards result from loss of each utility, and from simultaneous loss of two or more utilities?
3. What is the severest credible incident, i.e., the worst conceivable combination of reasonable malfunctions, which can occur?
4. What is the potential for spills and what hazards would result from them?

Location and Plot Plan

1. Has equipment been adequately spaced and located to permit anticipated maintenance during operation without danger to the process?
2. In the event of the foreseeable types of spills, what dangers will there be to the community?
3. What hazards are there from materials dumped into sewers of neighboring areas?
4. What public liability risks from spray, fumes, mists, noise, etc. exist, and how have they been controlled or minimized?

Adapted from: Guidelines for Hazard Evaluation Procedures.  Prepared by Battelle Columbus Division for The Center for Chemical Process Safety of the American Institute of Chemical Engineers. 345 East 47th Street, New York, NY. (1985).