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Riddle of the 1996 Puerto Rico Killer Propane Explosion Disaster
About 8:30 a.m. on Thursday, November 21, 1996, the six-story commercial Humberto Vidal building in Rio Piedras, a popular shopping and tourist district of San Juan, Puerto Rico, suddenly blew up, killing 33 people and injuring at least 80. The building’s first, second, third, and portions of the fourth floors shattered, dropping into the basement on top of the Humberto Vidal Shoe Store manager and the building’s long-time air conditioner technician. The administrator of nearby Chicken Kingdom restaurant knew what caused the explosion as the Puerto Rico police dispatched a bomb squad to investigate.
Police officers tending the intersection of Camelia Soto and Arzuaga Streets ran toward the building to help the injured and those trapped on the upper fifth and sixth floors, which remained relatively intact. Firefighters at the Rio Piedras fire station, about ¼-mile from the Humberto Vidal building, heard the explosion and arrived in a pumper truck about a minute later. They “observed cars turned upside down, injured and dead people in the street, and devastated buildings, but no fire. They radioed for assistance, and within minutes, additional fire, medical, and police personnel and equipment arrived. Firefighters provided first aid, removed bodies, and evaluated the risks of entering the building.” (1) Nearby Rio Piedras Medical Center received notification of the explosion at 8:42 a.m. and activated its disaster plan. Eventually local hospitals received 80 injured people. La Milagrosa School across the street became the triage site. Search and rescue teams activated, including representatives from the U.S. Federal Emergency Management Agency (FEMA, Urban Search and Rescue team) following declaration of a state of emergency by then U.S. President Clinton. (2) The Humberto Vidal building was unstable, necessitating discontinuation of rescue until structural engineers could asses the building. By 12:30 p.m. that same day, the engineers had identified those areas of the building believed to be stable enough for the workers to enter. FEMA staff extricated 10 bodies and located an 11th body too dangerous to recover. (2) By December 21, 1996, rescue workers removed the last four bodies, bringing the total number of dead to 33. The Salvation Army and the American Red Cross provided support services throughout the ordeal. A day after the explosion, a team including bomb-sniffing dogs from the U.S. Bureau of Alcohol, Tobacco and Firearms (ATF) examined the building and its debris for evidence of explosives. Samples of concrete, plaster, and a paint can examined at the ATF’s Forensic Science Laboratory showed no evidence of explosives and that damage to the building had resulted from a fuel-based explosion. (3) Puerto RicoPuerto Rico is a United States unincorporated territory with Commonwealth status. It shares common citizenship, common defense, and common currency. (4) Its population is around 4 million people (2006). San Juan, the capital of Puerto Rico, boasts a population of some 433,000 people. Rio Piedras was once a separate town south of San Juan but merged with San Juan in 1951. The population of Rio Piedras is about 9,400 people (2000 census). Since 1903, it has been the home of the main campus of the University of Puerto Rico. (5) Humberto Vidal, Inc.Humberto Vidal is a retail merchandise company that owns about 30 stores in Puerto Rico, selling shoes, socks, handbags, and related items. (6) Its administrative offices occupied the third, fourth, fifth, and sixth floors of the Humberto Vidal building in Rio Piedras. The first and second floors housed a jewelry store, a record store, and the Humberto Vidal Shoe Store. The Humberto Vidal building usually held about 50+ employees, including 37 who worked in the administrative offices, 7 in the jewelry store, 12 in the shoe store, and 2 in the record store. (7) Observers note that the death toll from the explosion was not higher because most stores were not open, few shoppers were in the area at the time of the explosion, and many employees in the Humberto Vidal building had not yet arrived for work. On a typical shopping day, hundreds of shoppers and tourists were near or in the building. U.S. National Transportation Safety Board InvestigationThe U.S. National Transportation Safety Board (NTSB), established in 1967, is responsible for investigating accidents involving aviation, highway, marine, pipelines, and railroads in the U.S. and its territories, including Puerto Rico. In January 1997, NTSB staff observed that damage inflicted on the Humberto Vidal building was consistent with overpressure (rather than fire) and that the area most affected by the heat was in the basement near an air conditioner exchange unit. The NTSB staff identified three possible sources of the fuel-based explosion:
The only propane tanks in the area were small cylinders located behind the Sbarro Pizza restaurant, just south of Chicken Kingdom restaurant. Investigators used pressure tests to confirm their integrity. No damage to the sewer system occurred and the smell of sewer system gas is distinctly different from the smell of the propane odorant that many witnesses smelled before the explosion. Thus, the NTSB staff concluded that the propane from the San Juan Gas Company’s distribution pipeline caused the explosion. The San Juan Gas CompanyThe San Juan Gas Company (SJGC) is a corporation wholly owned by Enron Corporation. “Enron was incorporated as Northern Natural Gas Company on April 25, 1930, in Delaware. In 1908, the corporate name was changed to InterNorth, Inc.; and in 1986, it was changed to Enron Corp. Petrolane Incorporated sold all outstanding stock of the SJGC, then a Delaware corporation, to The Protane Corporation; and it, in turn, on the same date transferred the assets to InterNorth, Inc. The SJGC continues to be managed and operated by its own slate of directors and officers, and its chairman is the CEO of an Enron affiliate operation.” (10) The SJGC distributed a 60 percent propane/40 percent air mix to customers in the greater San Juan area through 220 miles of gas mains, both low pressure (1/4 pound per square inch gauge, or psig, a unit of measure to indicate the pressure on a surface) to high pressure (20 psig) piping systems. (10) Low pressure systems primarily served Rio Piedras in about 6 miles of 4-inch diameter cast-iron gas mains and 3.2 miles of mostly 1¼-inch diameter galvanized steel service lines. The distribution system in Rio Piedras served about 500 customers, including Humberto Vidal. The NTSB staff learned that the service lines connecting the gas main under Camelia Soto Street onto which the Humberto Vidal building opened was made of bare steel and was not resistant to corrosion. Similarly, a tee-section connecting the plastic gas main on Camelia Soto to the service lines for the Chicken Kingdom and another building were not made of steel. (10) Infrastructure Underneath Camelia Soto StreetMany pipes and conduits run beneath Camelia Soto Street, including lines in use, lines for future use, and abandoned lines. Two water mains, a sewer main, a plastic gas line, telephone conduits, and electric conduits were (are) under there. Over the years, service providers had abandoned conduits, including a gas main, electric conduits, sewer laterals, and water service lines, without plugging or otherwise sealing them. Proper plugging would have prevented them from being paths for gases entering the soil. NTSB staff learned from Enron records that gas leakage was a big problem for years before the explosion. At least five of the conduits and pipes beneath Camelia Soto entered the Humberto Vidal building at its southwest corner and from there dove down into the basement.
In 1985, according to SJGC records, technicians installed a 1¼-inch polyethylene gas pipe on the opposite (west) side of Camelia Soto Street (on its east side were the Humberto Vidal building, Chicken Kingdom, and Sbarro Pizza). Later, gas company technicians extended the 1 1/4-inch gas pipeline in a 90 degree turn to provide service to the building in which Chicken Kingdom lived. In 1991, the Puerto Rico Aqueducts and Sewer Authority installed a 16-inch diameter water transmission pipeline under Camelia Soto Street but did not know about the 1¼-inch plastic gas pipe installed by the gas company in 1985. To make matters more interesting, the Puerto Rico Telephone Company in 1992 modified its facilities under Camelia Soto near the Humberto Vidal building. The telephone company held several meetings with the various utilities to ascertain the positions of water, sewer, and gas pipelines in the area. In spite of the diligence, the telephone company supervisor of the excavation project first learned about one pipe—the plastic one going to Chicken Kingdom—when a backhoe operator severed it. The gas company responded quickly to repair the damaged pipe and said that the company would probably abandon that section of gas line in the future. (11) “The project supervisor recalled that due to the existence of the gas line, he had to alter his construction procedures by placing some ducts side by side, rather than on top of one another. During the project, he said, he called the SJGC about five times and the SJGC had to repair about three leaks. He said that he often had to use his own excavation equipment to help the SJGC, as its employees did not bring a backhoe.” (11) Gas Leak SurveysThe San Juan Gas Company was supposed to perform leak surveys each year in high-density or commercial locations. However, technicians surveyed no part of Rio Piedras for propane-leaking gas pipes between 1994 and 1996. In 1996, technicians did survey it with a portable flame ionization detection unit that sampled the air from barholes drilled into the pavement. Technicians found and repaired 55 leaks. Of the 55 leaks, 13 were in the 12-block area around, but not adjacent to, the Humberto Vidal building. “Unaccounted for” gas is the difference between the quantity of gas that enters the gas system and the quantity that customers receive. The SJGC board of directors noted in 1996 that about 25 percent of its gas was unaccounted for, but attributed the loss to billing and metering problems (7 percent) and theft (18 percent) and none to leakage. (12) Propane Gas Most people know propane as the fuel in a white container attached to a barbecue
grill. Propane has many other uses, however, and has long heated homes and
heated water, dried clothes, fueled gas fireplaces and cooktops, and fueled
vehicles such as buses, some locomotives, forklifts and even taxis. People who inhale propane in concentrations of greater than 10 percent experience dizziness in a few minutes. High concentrations cause suffocation. (14) Many odorants are available to add to liquid gas to render it noticeable to people when a gas pipeline leaks. The San Juan Gas Company used the foul-smelling odorant ethyl mercaptan, whose intensity technicians tested monthly, albeit not in the way their procedures showed. If technicians add inadequate amounts of odorant, the gas will not have a smell and may go unnoticed during a leak. Records show that for some reason in January 1996, 11 months before the explosion, SJGC began conducting weekly odor intensity tests. (15) Some individuals with nasal perception problems may not be able to smell the odorant, even when it is present in sufficient amounts. Leaking propane may lose its odor as it passes through certain soils. Therefore, circumstances exist when some people are in the presence of leaking propane and are unable to detect the odorant. Reliance upon detection of odors to take action may not provide adequate warning of potentially hazardous concentrations. Corroded Leaking Propane InfrastructureThe NTSB investigators discovered a crack in the plastic 1¼-inch pipe in front of Chicken Kingdom. After testing, investigators determined that the pipe had been leaking propane at a rate of 1.70 cubic feet per minute (102 cubic feet per hour). (16) Investigators also found other significantly leaking gas pipes under the street, discussed elsewhere. (17) How Did Propane Enter the Humberto Vidal Building?Investigators were not able to determine the precise path the propane followed from the leaky pipes under Camelia Soto Street into the basement of the Humberto Vidal building. The cracked pipe leading to Chicken Kingdom was right above a 16-inch-diameter water line that technicians had installed in 1982. The propane could have followed this or many other conduits downhill toward the Humberto Vidal building to the north. Fueling the ExplosionInvestigators calculated a release of 36.7 cubic feet/hour of propane in front of Chicken Kingdom, assuming that only the propane released from this crack in the plastic pipe entered the Humberto Vidal building basement. They then calculated that this rate of release “would have taken about 57 hours for enough propane (2,100 cubic feet) to enter [the basement] to raise the gas-in-air level to 6 percent.” (18) The optimal fuel/air mixture in the basement at the time of ignition was about 5 to 6 percent gas in air, which would have provided a maximum-force explosion. The NTSB investigators concluded that the propane/air released from under Camelia Soto entered the Humberto Vidal basement was the fuel source for the explosion. The Human PerspectiveAstonishingly, employees and customers of the Humberto Vidal building AND Chicken Kingdom had complained to the San Juan Gas Company repeatedly about the smell of propane gas (actually the smell of the mercaptan odorant added to the gas) for at least seven days before the explosion. More than a week before the explosion, Chicken Kingdom employees told their supervisor about a strong smell of gas that came and went. The supervisor called the company that serviced his gas cooking equipment, which tested all of the equipment and found no problems. The equipment-company personnel “assumed that the odor must be associated with gas work going on along Camelia Soto, since someone was constantly there checking for gas leaks.” (19) The Chicken Kingdom administrator used a payphone to call SJGC, explaining the situation and that the smell of gas came and went. The gas company employee told the administrator that the gas company “would take care of the problem.” (19) The gas company employee did not ask for the Chicken King administrator’s name, whether the smell was inside or outside, or any other questions. After he made the report, the administrator saw a gas company truck and employees working in the area and assumed they had come in response to his call. On Thursday, November 14, 1996, one week before the explosion, the gas company’s 27-year veteran dispatcher acknowledged receipt of the first report about a gas odor at 8:15 a.m. from the Humberto Shoe Store manager. The manager said that he smelled gas “when he opened the store and that when he went to the basement, he could smell gas, although the odor was not very strong.” (20) The dispatcher told the manager to leave the basement door ajar and not to turn on anything having to do with electricity. A gas company technician arrived at 9:30 a.m. and walked down the basement stairs with the manager who pointed to a corner of the basement from which the gas smell was emanating. The technician turned on a detector, which “did not beep”, and left, saying that he could smell a slight odor on the street but not in the basement. The technician did not activate the detector before entering the enclosed space of the basement, which negated its efficacy. (20) On Friday, November 15, 1996, a gas company brigade arrived to the building at 8:15 a.m. and its 40-year-veteran gas company leader accompanied the shoe store manager into the basement. Neither could smell gas at the time and the gas company employee had no instrument to test the air in the basement. However, he did go outside to survey the underground with a combustible gas indicator, which he inserted into barholes 12 to 18 inches deep and about four feet apart, freshly dug by the crew. (A barhole is a small-diameter hole made in the ground along the route of a gas pipe in a bar test survey.) The main pipe carrying the liquid propane under pressure was some 2-3 feet below the road surface. The discrepancy between the depth of the barholes and the actual main was important because propane gas sinks. The brigade leader said that the combustible gas indicator read zero except at one or two spots where it registered at 2 to 3 percent on the lower end of the lower explosive limit scale. The crew probed the gas main going down Camelia Soto, along which the gas indicator registered zero; supposedly capped off an old line going to the Humberto Vidal building; used soap solution to test the gas main for leaks and found none, and left, telling the manager to call again if he smelled more gas. On Monday, November 18, 1996, a Humberto Vidal employee again complained to the Humberto Shoe Store manager that the smell of gas in the shoe store was strong. The manager replied that he had notified the gas company and that it was not paying much attention. The manager and employee descended the stairs, whereupon the employee became so dizzy and nauseated that they had to return back upstairs to get fresh air. Tuesday, November 19, 1996, was a holiday, and the shoe store was not open.On Wednesday, November 20, 1996, the same employee again smelled gas and refused to descend the stairs into the basement because she was afraid. Someone again called the gas company, which again sent another brigade because “they [employees at the Humberto Vidal Building] keep on calling.” (20) The manager told a Humberto Vidal official about the odor. The official told him to open the door or get some fans if the smell got worse, as “he did not want customers to smell the gas.” (20) The manager could not leave the door to the store open because he was unable to watch the merchandise if the door were left open. The brigade leader on November 20, 1996, was a four-year employee of the gas company who went into the basement without a detector, but did detect a smell, which he quickly attributed to rubber shoes stored there. (Humberto Vidal employees at the time were unpacking shoes to put them onto the shelves of the store.) Humberto Vidal employees said that the smell was in addition to the smell of rubber from shoes. The smell in the basement was so strong, employees stacked merchandise arriving at the store that day on the first floor instead of in the basement. (21) The brigade made new barholes along multiple streets, but found no indications of combustible gas in them. It did not probe the gas service to the Chicken Kingdom because it did not know there was a gas service to that establishment. The leader did not call the dispatcher to learn the locations of gas pipes in the area, nor did he use a pipe locator, the maps in his truck, or other means to locate the gas lines. (21) Meanwhile Humberto Vidal employees continued to smell the odor of propane gas (odorant) in rooms in the building. The brigade again returned to the area and re-tested all of the new barholes made by the crew earlier that morning. Again, they showed no signs of combustible gas. On Thursday, November 21, about 6:45 a.m., a father and son air conditioning contractor, which had worked for the Humberto Vidal office for 10 years, arrived to perform routine monthly maintenance of the air conditioners. The manager smelled gas, but switched on the lights without consequence and took the elevator with the father and son air conditioner technicians. Later the son said that he might have smelled rubber, but not gas, when he arrived to the building that morning. He completed his work at 7:40 a.m. and left. Many employees continued to smell gas. The gas company sent a third brigade, led by a four-year employee of the gas company, reassessed the previous set of barholes, drilled some more (18 inches deep), and still found no evidence of combustible gas. The administrator of Chicken Kingdom saw the gas company brigade and noticed about a half hour before the explosion a “little” gas odor in the store when the breeze blew into the store. The brigade leader then had some barholes drilled at the corner of Camelia Soto and de Diego streets where upon he measured 20 percent on the has scale with his combustible gas indicator, but still did not smell the odor of gas. Then the explosion occurred, around 8:30 a.m., lifting him into the air and throwing him about 15 to 20 feet to the north. U.S. National Transportation Safety Board DeterminationsThe National Transportation Safety Board determined that the probable cause of the propane gas explosion was an earlier excavation-caused gas leak that permitted propane gas to flow downhill to fill the basement of the Humberto Vidal office building. In addition,
One of the most important factors contributing to loss of life was the failure of people to leave the area even after they detected the odor of gas for an entire week. Brief SummaryAging infrastructure is a hazard. Aging infrastructure is everywhere. If you smell gas, leave the area immediately and call the authorities. Do not use any electrical appliances (e.g., air conditioner); do not smoke; and do not connect or disconnect any appliance or any other source ignition or flame. Do not try to repair or stop the gas leak yourself; move to a safe place against the wind and wait for the arrival of the gas company personnel; and inform others in the area about the possibility of a gas leak. (22) Gas company personnel are the experts in gas leak situations. (23) San Juan Gas Company personnel in the week leading up to the explosion were supposed to be responsible for “taking immediate and effective action in all emergencies, such as when gas is detected inside or near buildings, when there is a fire or explosion in or near gas lines, or when there is a natural disaster. (22) Moreover, the field supervisor was supposed to be responsible for determining which of the following kinds of action were appropriate: “evacuating, eliminating all sources of ignition, ventilating the area, locating the gas leak, repairing the gas leak, coordinating the work with firemen, police, civil defense, etc., and helping control traffic and crowds in the area.” (22) Five gas company employees sustained injuries in the explosion. Notes:
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