Petroleum Industry

Accident Review

CASE REVIEW #1

TANK DISPOSAL

A company that removed and collected empty fuel tanks to cut them into scrap metal lost two men in two separate accidents within a three month period. The following case review (the second accident) is a compilation of information provided in several articles that were published in The Indianapolis Star.

Company employees were purging vapors and cutting tanks open when the accident occurred. A tank that investigators suspect had either not yet been cleaned or that had been cleaned improperly exploded while a company employee was cutting an adjacent tank with an acetylene torch. The explosion caused the tank to push forward into the tank being worked on by the employee, crushing the employee between the tank he was working on and a wrecker parked nearby.

Reporters investigating the incident interviewed witnesses. These witnesses stated that it was not uncommon to hear five or six small explosions a week at the facility, though the fatal explosion was especially loud. This explosion was powerful enough to launch a section of the tank onto neighboring property where it struck the roof of a construction company building.

CONCLUSIONS:

The use of a cutting torch to dismantle a tank having contained a flammable or combustible liquid is never a good idea. Even tanks that have been entered and cleaned can contain enough product in the rust scale and overlapping seams to redevelop an ignitable atmosphere. Tanks removed after merely pumping out the product to the greatest extent possible (the most common method used by removal contractors) will always contain substantial residue capable of generating an ignitable atmosphere.

Inerting agents (i.e. nitrogen or carbon dioxide), used to make tanks safe for removal, will not make tanks safe for hot work. Inerting a tank does not eliminate flammable vapors, it creates an oxygen deficient atmosphere. Small holes in the tank can cause the reintroduction of oxygen. Cutting the tank will allow oxygen to be reintroduced to the tank interior where they can mix with existing flammable vapors to create an ignitable vapor to air mixture.

Petroleum vapors are significantly heavier than air and will accumulate at ground level if not properly dispersed. Ventilation of tanks where the vapors are discharged to near to the ground or with insufficient velocity can cause the accumulation of flammable vapors at grade level. Additionally, tanks which have been cut open and that are no longer being ventilated will continue to create flammable vapors, potentially resulting in both an accumulation of vapors within the tank and allowing flammable vapors to flow out the opening and accumulate at grade level. These vapors can create a “fuse” leading from areas where hot work is being performed to the tank. The accumulation of vapors within the tank can cause the tank to become a de facto bomb.

The occurrence of routine small explosions should have served as an indication that the procedures in use by the company were inherently dangerous. The company should have investigated the cause of any minor explosion and adjusted their procedures to incorporate controls capable of eliminating these near misses.

CASE REVIEW #2

TESTING LEAK DETECTORS

A technician performing tests of leak detectors was injured and lost a day and a half of work due to a burned cornea. The station where the tests were being performed had multi-product dispensers. The operating levers for the product being tested were secured to prevent customers from activating the submerged pump. The technician did not turn off the submersible pump circuit breaker. When the plug was removed from the emergency impact valve, gasoline sprayed into the technicians face and eyes. The circuit breaker was located and turned off while the technician held back the flow of gasoline with his hand. Investigation determined that a defective relay board in the dispenser had kept the submersible pump activated constantly.

CONCLUSIONS:

The technician did not practice appropriate lock out/tag out procedures. The procedure utilized by the technician can be likened to turning off a light switch prior to changing the fixture without turning off the breaker. Redundancy in procedural protection is necessary to provide protection against unforeseen circumstances.

Eye protection needs to be a standard piece of personal protection worn by anyone potentially exposed to liquids that can spray, splash, spew or otherwise become airborne (or any other eye hazard for that matter). Properly fitted eye protection could have prevented the injury to the employees eyes.

When working at a service station, workers need to be especially vigilant in preventing releases of flammable product. Extra steps are necessary due to the proximity of the general public. The public can not only be adversely affected by such an incident, but can introduce additional risks due to idling engines and smoking. Where flammable liquids such as gasoline are released, ignitable vapor mixtures can form. Additionally, gasoline saturating into the clothing of a worker so exposed can present a real risk of severe burn injuries.

CASE REVIEW #3

NEW TANK AIR TEST

A plumbing company was preparing to install fiberglass tanks at a convenience store. Prior to installation, the tanks were required to be air tested. The employee was under the erroneous impression that the air test required applying 80 psig of air pressure to the tank interior. The pressure gauge had already reached 40 psig when the employee complained that pressurizing the tank was taking too long and left for lunch with the air compressor still running. Twenty minutes later, the tank blew apart.

The explosion sent two residents to the hospital and damaged about a dozen cars. The 12,000 gallon tank broke into two pieces. The end cap dome of the tank traveled 110 yards to the north where it landed on a parked truck. The remainder of the tank, 8 feet in diameter and 30 feet long, was blown half a block to the south.

CONCLUSIONS:

Proper training is essential to all petroleum service industry personnel in order to protect themselves and the general public. Written manuals illustrating each step of the tasks to be performed on site need to be available for review and a chain of command needs to be established for each site. The maximum allowable pressure for air-testing of new tanks prior to installation is 5 psig. This information is usually provided by the manufacturer or even attached to the tank body. Training and supervision need to be in place to avoid this type of accident.

Procedures and equipment need to be instituted to eliminate serious risks to site personnel and the public. Standard procedure for air-testing of tanks should include the use of pressure relief valves set at 6 psig. Supervision should ensure that employees without adequate experience are not endangering others due to their inexperience during any operation with potential health consequences to site personnel, the public or the environment.

Equipment should not be left unattended during operation.

CASE REVIEW #4

TANK DISMANTLING

Summary of articles that appeared in Tulsa World and the Chicago Tribune.

An explosion in an empty underground tank killed a worker as he was dismantling it with an acetylene torch. The tank had been removed from the ground the week prior to the explosion and dry ice had been placed in it to make the tank inert. The plumbing company returned to begin dismantling the tank, assuming that the vapors had been displaced by the dry ice. The 2000 gallon steel tank exploded when the worker, employed by the plumbing contractor, applied an acetylene torch to it. The end cap of the tank separated from the body with such force that the worker was pushed backwards 25 feet into a building. The worker’s death was attributed to the trauma suffered when driven into the building by the explosion. In addition to the fatality, the building was damaged as was a truck used by the plumbing contractor on site.

CONCLUSIONS:

Assuming that a potentially hazardous situation is safe should never be done (assume = ass + u + me). A simple measurement with a meter to determine oxygen content and flammable vapor concentration would have disclosed that any method of cutting open the tank would unduly expose site workers to potential explosion hazards.

CASE REVIEW #5

TANK INSTALLATION

A tank installation company was preparing to place a 10,000 gallon tank into an excavation on a day when heavy rains were forecast for the evening. The decision was made to have a trucking company haul water in to ballast the tank. The transport company delivered about 9000 gallons of water into the tank. The following morning, the installation company crew was trimming out the tank. An employee using an air grinder to clean the fill pipe was blown several feet from the tank when an explosion occurred without warning. The employee suffered third degree burns to both hands and missed several weeks of work.

The ensuing investigation revealed that the transport company had hauled gasoline previous to delivery of water to the site without flushing the tanker between deliveries. Gasoline floats on water (specific gravity < 1) and created sufficient flammable vapors in the air space (flash point = -45 F) to create the explosive atmosphere.

CONCLUSIONS:

It is hard to prevent accidents such as this one, which could be termed “unforeseeable”. This accident illustrates just how easily an accident can occur. The fact that eye injury did not occur can probably be attributed to the proper use of safety glasses. The use of an air tool, as used in this incident, will not eliminate the potential for igniting a flammable atmosphere; however, the use of an electric tool is more likely to introduce a spark of sufficient ignition energy than an air tool (electrical current flowing through the on/off switch will arc immediately prior to being placed in the “on” position and as the switch is being placed in the “off” position).

The presence of third degree burns to both hands as a result of a sudden flash explosion could probably only result when work gloves were not in use.

CASE REVIEW #6

LEAK DETECTOR INSTALLATION

Two petroleum service company employees were installing leak detectors at a service station. The foreman was having a difficult time removing piping in the manway. In order to proceed more quickly, the foreman elected to use an electric saw to cut the piping. The laborer warned the foreman of the danger and potential for fire or explosion. When the foreman turned on the saw, gasoline vapors in the manway ignited causing a flash fire.

The laborer pulled the foreman from the manway, extinguished the fire with a portable fire extinguisher and applied cold water to the foreman’s burns. The foreman suffered second degree burns to his face, chest and arms causing him to miss several days of work. Only the quick action of the laborer on site in extinguishing the fire prevented the possibility of a major explosion or dangerous deflagration.

CONCLUSIONS:

The area within the manway must be monitored to assure a safe working environment. Indications that flammable vapors have accumulated within the manway area require that some method be used to disperse the vapors (such as ventilation) and make the space safe prior to entry. On-going monitoring of the space must be performed to ensure the adequacy of the vapor dispersal.

When working around flammable materials such as gasoline, the use of non-sparking and explosion proof or intrinsically safe tools is a requirement. Switches on electrical tools have the potential to arc and cause ignition of flammable vapors. Explosion proof and intrinsically safe designs eliminate the ability of the tool to act as a source of ignition. Tools made from non-sparking materials do not spark on impact. Pneumatic tools will not produce an electrical arc at start up as the switch is not electrically controlled.

The foreman did not adhere to the “buddy system”. Rather than giving consideration to the warnings of his coworker, he chose to ignore his recommendations due to his impatience with the situation. In an ideal setting, each worker should be empowered to shut down the job if something is perceived as dangerous. The recognition of the fire or explosion potential was apparent due to sufficient fire fighting media (fire extinguishers) at the manway to extinguish the fire. The valid warnings of the coworker should not have been ignored. If there was reason enough to disregard the warnings of the coworker, the reasons for not implementing a change of procedure should have been explained to him prior to continuing with the work at hand.

CASE REVIEW #7

TANK REMOVAL

On May 23, 1986, the last of three underground storage tanks was being removed from an abandoned gasoline station in Portland, Maine by a company regularly engaged in such work. The station was located in an area where surrounding structures were in close proximity to one another. There was little air circulation at the site due to the surrounding buildings and still air (no appreciable wind). A vacuum truck was used at the location to suction out remaining fuel and to ventilate the tanks while they were being opened and cleaned. The vacuum truck had no way to contain the vapors being displaced from the tank and discharged them near grade level. An access opening had been partially cut through the end of the tank, but the last blade had been expended prior to completion of the access opening. A laborer was directed to radio for more saw blades from another location. The radio was located in one of the pick up trucks on site. The laborer got into the truck and turned on the ignition in order to operate the radio. When he did, an explosion occurred under the hood of the truck and a second explosion occurred almost immediately at the tank. The second explosion caused the end cap of the tank to separate from the body of the tank and the body of the tank spun around, striking a laborer and killing him. Three other laborers were injured due to burns and/or lacerations caused by the explosion. The vacuum truck and a pick up truck on the site caught fire and a large number of windows in the surrounding buildings were shattered.

CONCLUSIONS:

There were numerous problems with the way that this job was conducted. First, the ventilation system used at the site was inadequate. Second, no monitoring of the area for flammable vapors was conducted. Third, the truck was a potential source of ignition that should not have been located in an area where flammable vapors could accumulate.

Gasoline vapors are several times heavier than air. Because of the potential for the vapors to settle in low-lying areas and accumulate to levels that could be ignited, ventilation is required to be designed to discharge vapors in a way that will prevent this type of accumulation. Regulatory requirements for discharging flammable vapors state that the vapors need to be discharged a minimum of 12 feet above grade and no less than 2 feet above adjacent structures (such as roofs and canopies). Because there was little or no natural air movement, it may have been necessary to discharge vapors even higher than 12 feet above grade to assure that they were dissipating properly. Instead, the vapors were discharged near grade.

In order to properly assess the effectiveness of the ventilation method at discharging vapors in a manner that prevented reaccumulation, monitoring of the work area for the presence of flammable vapors should have been conducted. Since the lower flammable limit (LFL) for gasoline is approximately 1.4% (14,000 ppm), it is hard to understand how the presence of such strong vapors could have been ignored by site personnel. When working around flammable vapors, the noting of distinct aromas consistent with the flammable material should cause alarm (not only because of the potential for fire or explosion, but also due to the potential for exposure to toxic levels of contaminants).

Vehicles and heavy equipment on site need to be staged in areas where they are unlikely to cause problems. Site workers need to be instructed in the potential hazards posed by heavy equipment and vehicles on site. Vehicles can act as sources of ignition due to backfiring, turning of the ignition switch and scraping of parts on paved surfaces (dragging a muffler, scraping a bucket, etc). Other vehicular/heavy equipment hazards include: running into or over site personnel, entanglement in overhead power lines, and spillage of loads.

CASE REVIEW #8

HEAVY EQUIPMENT

A site worker was severely injured when pinned between a track hoe operated by his brother and a back hoe parked on site. The injured worker assumed that the track hoe operator was aware of his location when he stooped down to pick up a tool that had fallen on the ground. When the track hoe operator realized that he had struck the worker, he attempted to back away from him, but had forgotten which direction the cab was faced on the tracks during the ensuing panic. Thus, instead of making the situation better, he made the situation worse by advancing further onto his legs. His brother suffered multiple fractures to both legs (compound/complex), several small broken bones in his feet and a shattered ankle. Because he was wearing appropriate safety boots with steel toes and shanks, the injuries to his feet were mostly minor. Because the damage to the foot on the leg with the shattered ankle was so minor, the doctor attempted (successfully) to save the ankle and foot rather than amputate.

CONCLUSIONS:

Because track hoe cabs rotate on their tracks, the track hoe beeps in both directions of travel. This caused the injured worker to ignore the movement of the track hoe, assuming it was moving away from him. This can also happen to site workers where multiple pieces of heavy equipment are in operation and the backup alarms are beeping constantly. Operators of heavy equipment have larger and more blind spots than drivers of passenger vehicles. When heavy equipment is in operation on a site, there should be someone charged with directing the operator and workers that are not required to work in close proximity to the heavy equipment should keep their distance. The tool could have been picked up at a later time when the heavy equipment was either no longer in operation or was operating in a different location.

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