Major leaks

The bursting of a large pressure vessel at Feyzin, France, in 1966 was at the time one of the worst incidents involving LFG that had ever occuired but has since been overshadowed by the events at Mexico City (see Section 8.1.4). It caused many companies to revise their standards for the storage and handling of these materials. Because no detailed account has been published, it is described here. The information is based on References 3 through 6 and on a discussion with someone who visited the site soon after the fire. 

A visible cloud of vapor, 1 m deep, spread for 150 m and was ignited by a car that had stopped on a nearby road 25 minutes after the leak started. The road had been closed by the police, but the driver approached from a side road. The fire flashed back to the sphere, which was surrounded by flames. There was no explosion. The sphere was fitted with water sprays. But the system was designed to deliver only haif the quantity of water normally reeommended (0.2 U.S. gal/ft- min. or 8 L/m min.), and the supply was inadequate. When the fire brigade started to use its hoses, the supply to the spheres ran dry. The firemen seemed to have used most of the available w ater for cooling neighboring spheres to stop the fire from spreading, in the belief that the relief valve would pro-teet the vessel on fire. 

The ground under the sphere was level so that any propane that did not evaporate or burn immediately collected under the sphere and burned later. 

Ninety minutes after the fire started, the sphere burst. Ten out of 12 firemen within 50 m were killed. Men 140 m away were badly burned by a wave of propane that came over the eompound wall. Altogether, 15-18 men were killed (reports differ), and about 80 were injured. The area was abandoned. Flying debris broke tbe legs of an adjacent sphere, w hich fell over. Its relief valve discharged liquid, which added to the fire, and 45 minutes later this sphere burst. Altogether, five spheres and two other pressure vessels burst, and three were damaged. The fire spread to gasoline and fuel oil tanks. 

At first it was thought that the spheres burst because their relief valves were too small. But later it was realized that the metal in the upper portions of tlie spheres was softened by the heat and lost its strength. Below the liquid level, the boiling liquid kept the metal cool. Incidents such as this one in which a vessel bursts because the metal gets too hot are known as Boiling Liquid Expanding Vapor Explosions or BLEVEs. 

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A preliminaiy air test at not more than 0.17-MPa (25-lbf iu ) gauge pressure may be made prior to hydrostatic test in order to locate major leaks. 

One has to be aware of the danger of asphyxiation from gases in inerted equipment. This is also important For surrounding areas in case of major leaks. 

In 1977. the technical press reported that a major leak from a 20,000-m liquefied propane tank in Qatar had ignited and that the resulting fire and explosion had killed seven people and caused extensive damage to the rest of the plant [18]. There had also been a leak the year before, but it had not ignited, and the tank had been repaired. The propane was stored at -42°C and atmospheric pressure. No detailed report on the incident was issued, for legal reasons, but a member of the company concerned published several papers [19-21], which gave new recommendations for t,he construction of tanks for refrigerated LFG, and it is thus possible to read between the lines and surmise what probably happened. 

The leak size can be reduced by using double mechanical seals or a mechanical seal and a throttle bush, the space between the two being vented to a safe place. Major leaks may still occur, however, due to collapse of the bearing or seal. LFG pumps should therefore be fitted with emergency isolation valves (see Section 7.2.1), particularly if the temperature is low or the inventory that can leak out is high. 

Davenport [1] has listed more than 60 major leaks of flammable materials, most of which resulted in serious fires or unconfined vapor cloud explosions. Table 9-1, derived from his data, classifies the leak by point of origin and shows that pipe failures accounted for half the failures— more than half if we exclude transport containers. It is therefore important to know why pipe failures occur. Following, a number of typical failures (or near failures) are discussed. These and other failures, summarized in References 2 and 3, show that by far the biggest single cause of pipe failures has been the failure of construction teams to follow instructions or to do well what was left to their discretion. The most effective way of reducing pipe failures is to ... 

Sentinel holes are used as a simple form of thickness testing. A small hole of about I - 6 mm diameter is drilled from the outer wall of the piece of equipment to within a distance from the inner wall (in contact with the corrodent) equal to the corrosion allowance on the equipment (Fig. 9.11). The technique has been used even in cases where the corrodent spontaneously ignites on contact with the atmosphere. The philosophy is that it is better to have a little fire than a big one which would follow a major leak from corrosion through the wall. When the sentinel hole begins to weep fluid a tapered plug is hammered into the hole and remedial maintenance planned. Siting the sentinel holes is somewhat speculative although erosion at the outside of a pipe bend is often monitored in this way. 

Major leaks at pump seals, valve stem packing, flange gaskets, etc. 

Major leak from a propane compressor seal... 

Emergency shutdown Describes the procedure used to shut down the equipment if an emergency should occur. This includes major leaks, reactor runaway, and loss of electricity, water, and air pressure. 

Preliminary Pneumatic Test. A preliminary test using air at no more than 170 kPa (25 psi) gage pressure may be made prior to hydrostatic testing to locate major leaks. 

If cylinders are to be brought into the laboratory, they should only be transported on purpose-built trolleys, to which they can be securely chained during transport. Acetylene cylinders must be kept more or less vertical, for reasons discussed in Chapter 2, section 5. The total number of cylinders in the laboratory at any one time must be kept to the minimum possible, especially for fuels and oxidants, and in routine use all cylinders must be securely chained or strapped to a bench or wall. They should be positioned for easy access and so that they will not block a rapid exit. It is perfectly feasible to run two flame spectrometers from a single acetylene cylinder, via a T junction, although individual flash-back arrestors should be fitted in the lines to both instruments. If an acetylene cylinder is used inside the laboratory, it is especially important to check for gas leaks whenever the cylinder head is changed. Don t rely on the smell of escaping gas, which will only detect fairly major leaks. Use of a paint brush and a soap solution is more reliable, as bubbles will be clearly seen if gas is escaping. 

The procedure for establishment of the interface is variable because of the possibility of small leaks from the inner compartment (major leaks are easily observed). 

Davenport has listed more tlian 60 major leaks of flammable materials, most, of which resulted in serious fires or mconfimd vapor cloud explosions (UVCEs)/ Table 16.3.1 classifies the leaks by point of origin and shows that if transport containers are excluded, pipe failures accounted for more than lialf tlie accidents. The biggest cause of tliese failures lias been shown to be poor construction due to use of wrong specifications or failure to follow specifications established. 

Exposures associated with emergency situations major leaks, major spills, and equipment malfunctions. 

When our system was first set up, there was a leak at the pump outlet. It was not a major leak, but it was significant enough to have to be fixed. We decided to wait a few days however, after a few days the leak had stopped. We have observed this same phenomenon in several of our earlier systems. What may happen is that the pressure within the system forces the tape and or thread sealant to form a barrier and thus stops the leaking. There was... 

PERSONAL PROTECTION wear impervious protective clothing, including boots, protective gloves, lab coat, apron or coveralls use chemical safety goggles a system of lo-cal/mechanical exhaust ventilation is recommended to control emissions at the source and to prevent dispersion into the general work area in event of major leak, self-contained breathing apparatus may be required maintain eyewash fountains and quick-drench facilities in work area. 

The environmental risks may be reduced if current research on the use of fertilizer solutions in place of salt solutions for non-convective gradient type solar ponds is successful. Even though the raw material costs are higher, reduced environmental effects of a major leak in a farming area offer a great incentive for further development. 

The unit is fully protected with safety valves at necessary points. In addition the compressor has water temperature and pressure shutoff switches, and a suction pressure switch, which will shut it down in the event the system runs low on gas. This protects against line bursts or major leaks, or operator negligence in providing gas supply. The expander has overspeed and oil-pressure protection. The expander and compressor are linked with a unique electrical circuit, which permits them to be started separately, but which shuts down both units in case of automatic shutdown of either one. Thus any failure will close down the entire system, preventing damage to either compressor or expander. 

One tank should always be empty to collect any major leak of add or oleum. 

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