Cause analysis of Huangdao oil depot accident

The direct cause of the catastrophic fire accident in Huangdao oil depot is that the nonmetallic oil tank itself has defects, and it is struck by lightning to the ground, resulting in induction sparks to detonate oil and gas.

After the accident, two semi-underground concrete stone tanks No.4 and No.5 collapsed, and metal tanksNo. 1, No.2 and No.3 collapsed, which brought great difficulties to on-site investigation and accident cause analysis. On the basis of excluding man-made damage, open flame operation, electrostatic detonation and other factors, on the basis of good grounding of lightning rod, according to the meteorological conditions at that time and the testimony of relevant personnel (it was thunderstorm weather in Qingdao at that time), after in-depth investigation and scientific demonstration, the focus of the accident was lightning strike. There are six main forms of concrete oil tanks being detonated by lightning: one is spherical lightning; The second is that the induced voltage of lightning rod is directly hit to produce sparks; Third, lightning strikes directly ignite oil and gas; Fourthly, the lightning discharge in the air causes the induced voltage to spark; The fifth is direct thunder; Sixth, the lightning induced voltage around the tank farm produces sparks.

Through the investigation and comprehensive analysis of the above lightning strike forms, it is found that the first four lightning strike forms have been ruled out as the cause of the explosion and fire of No.5 oil tank, and the possibility of the fifth lightning strike is extremely small. The reasons are as follows: the shielding failure rate of shielding failure is 0.4% in flat land and 1% in mountainous area, and the probability is very small; The characteristic of shielding failure lightning is that lightning shielding failure is small, and the higher the lightning rod, the greater the possibility of shielding failure. At that time, the lightning intensity in Qingdao was moderate, and the height of lightning rod in No.5 tank was 30 meters, which was low, so the possibility of shielding failure was not great. After on-site excavation and inventory, no trace of lightning strike is found on the tank body, and shielding lightning can also be eliminated.

The cause of the accident is most likely due to the induction spark generated by lightning strike on the ground in the reservoir area to detonate oil and gas. Based on:

① At 9: 55 am on August 1989 and 12, six people witnessed it from different places. Lightning struck the ground in this area before the No.5 oil tank caught fire.

② According to the measurement of the Space Center of Chinese Academy of Sciences, there were two or three lightning strikes in this area at that time, and the maximum current was 104 A. ..

(3) With the extension of the service life of the tank body structure and roof facilities of No.5 oil tank, the cracks and protective layers of the precast slab fall off, exposing the steel bars. At the top of the tank, the joint of the anti-induction lightning shielding net is fixed with iron clips. The oil sample hole is covered with 9 layers of barbed wire. The electrical connection between steel bars and metal parts in No.5 tank is unreliable in many places, and there is the possibility of spark discharge due to induced voltage.

(4) According to the electrical principle, lightning induction in the air or on the ground 50-60 meters away can discharge the gap of electrical facilities of100 ~ 200mm. From the metal gap of No.5 oil tank, when lightning strikes the ground within several hundred meters around, as long as there is an induced voltage of several hundred volts, spark discharge can be generated.

⑤ When a fire broke out in No.5 oil tank from 2 am to 9: 55 am on August 2, crude oil was imported15000m3. At the same time, a certain volume of oil and gas will inevitably be discharged around the top of the tank, so that a layer of oil and gas reaching the explosion limit will be formed on the top outside the tank. In addition, according to the principle of oil and gas stratification, although the oil and gas in most spaces in the tank are at the upper explosion limit, due to the uneven distribution of oil and gas, the oil and gas concentration in the vent holes and cracks in the tank is low, but it is still within the explosion limit. In addition to the above direct causes, it is necessary to analyze the cause of the accident from a deeper level, draw lessons from the accident, and nip in the bud.

① The storage scale of Huangdao oil depot is too large and the production layout is unreasonable. Huangdao covers an area of only 5.33 square kilometers, but there are two oil depots, Huangdao Oil Depot and Qingdao Port Authority Oil Port, which are distributed on a slope less than 1.5 square kilometers. As early as 1975, the oil storage scale of 34 1 10,000 cubic meters was formed. However, since 1983, the relevant state departments have successively issued indicators and investments, so that the oil storage scale of Huangdao reached 760,000 cubic meters before the accident, forming a layout with connected oil depots and dense oil tanks. Five oil tanks in the old tank farm of Huangdao Oil Depot were built on the hillside, and the oil transportation production area was built at the foot of the nearby mountain. This design only considers the use of natural height difference to save electricity, but ignores the fire safety requirements, which affects the observation and inspection of oil tanks. Moreover, in the event of an explosion and fire, the production area will be affected first and will be destroyed. This not only left a long-term hidden danger to the safety of Huangdao oil depot, but also posed a permanent threat to the safety of Jiaozhou Bay.

(2) the concrete oil tank is inherently deficient, and the congenital defects are not easy to rectify. No.4 and No.5 concrete tanks of Huangdao Oil Depot were built in 1973. At that time, the lack of steel in China was the product of design, construction and production under the guidance of combat readiness. The internal reinforcement of this concrete oil tank is complex, and metal parts such as light holes, oil and gas breathing holes and fire pipes are all over the top of the tank. After a certain number of years of use, the concrete protective layer falls off and the steel bars are exposed, which is easy to induce lightning and spark at the binding and discontinuity of the steel bars. If the surrounding oil and gas is within the explosion limit, it will cause an explosion. The concrete tank body is very loose. With the extension of service life, cracks appear in the prefabricated arch plate at the top of the storage tank, forming criss-crossing oil and gas leakage pores. Most concrete oil tanks are atmospheric oil tanks. Due to the limitation of bearing capacity, the tank top needs to be provided with vent holes to relieve pressure. The vent hole is directly connected with the atmosphere, and oil and gas are often distributed around the top of the tank, forming an oil and gas layer, which is a potential risk factor.

(3) Concrete oil tanks only pay attention to the oil storage function, and most of them are relatively simple, ignoring fire safety and lightning protection design, with low safety factor and being vulnerable to lightning strike. 1July, 985 15, after the No.4 concrete oil tank of Huangdao oil depot was struck by lightning and caught fire, in order to learn a lesson, four 30 cubic meters high lightning rods were respectively erected around No.4 and No.5 concrete oil tanks, and an inductive lightning shielding net was installed at the top of the oil tanks. Because the oil tank is in use, the grid joints cannot be welded, and they are all pressed by iron clips. This investigation found that most compaction points were seriously corroded. When the compaction point is measured after the fire, the resistance value is as high as 1.56 ohm, which is far greater than the specified value of 0.03 ohm.

(4) The fire protection design is wrong, the facilities are backward, the strength is insufficient, and the management can't keep up. Huangdao Oil Depot is the key unit of fire protection, and the fire preparation system is mainly based on the installation of fixed fire protection facilities on oil tanks, supplemented by two foam fire truck and/kloc-0 tankers. The fire fighting system of No.5 concrete oil tank consists of a foam pump with a flow rate of 900 tons/hour and a pressure of 784 kPa, and four rows of 20 foam automatic generators installed at the top of the oil tank. When the accident happened, the oil depot fire brigade rushed to the oil tank, which took less than 10 minutes. The crude oil just exploded is not very hot, and the light blue flame jumps on the oil surface, which is a good opportunity to organize fire fighting and rescue in time. However, the fire-fighting facilities installed on the top of the tank are difficult to check and maintain at ordinary times, and it is impossible to do performance injection tests regularly, and they cannot be used until the last moment. Foam fire truck, the oil depot itself, didn't put out the fire in an emergency, and it was a drop in the bucket for a foam fire truck to face a small fire. The fire passage between oil tanks in the reservoir area is a narrow and uneven hillside road, and there is no circular road, so there is no room for fire engines to turn around, which hinders the possibility of using fire engines to rescue and extinguish fires. There are 35 firefighters in the oil depot, 24 of whom are temporary contract workers of farmers. Due to the lack of necessary training and poor technical quality, 12 people left the locomotive depot for home in July 12, resulting in a serious shortage of firefighters in the oil depot.

⑤ There are many loopholes in the safety production management of oil depots. Since 1975, there have been many lightning strikes, oil spills and fire accidents in this warehouse. Fortunately, it was discovered in time and did not lead to serious consequences. 1On March 5th, 988, the former Ministry of Petroleum issued the Regulations on Safety Management of Fire Prevention and Explosion Prevention in Drilling, Development, Storage and Transportation of Oil and Gas. However, the safety section of Shengli Oil Transportation Company, the superior competent unit of Huangdao Oil Depot, did not issue this regulation to Huangdao Oil Depot. In the thunderstorm hours before the accident, the oil depot has been transporting oil, and the leaked oil and gas has aggravated the danger of lightning strike and fire. The metal tanks 1, 2 and 3 in the oil depot were designed to be 5000m3, but in the construction stage, the original design tank farm was rebuilt to10000m3 only by the personal will of a leader in Shengli Oilfield. In this way, the actual tank spacing is only 1 1.3m, which is far less than the 33m spacing specified for safety and fire prevention. Qingdao Public Security Bureau issued four notices of fire hazards in the past ten years, demanding rectification within a time limit and stopping using No.2 tank halfway. But until the accident, No.2 cabin never stopped. In addition, the requirements for employees are not strict, workers' labor discipline is slack, and violations of discipline occur from time to time. 12 During the thunderstorm in the morning of August, the firemen on duty did not patrol their posts, but played poker and watched TV indoors. In the event of an accident, the self-rescue ability is poor, and the coordination with public security fire fighting is weak.