Welding, ignition

An approximate equilibrium is set up in the plasma, with the electrons, ions, and atoms having velocity distributions similar to those of a gas that has been heated to temperatures of 7,000 to 10,000°C. Since the plasma is ignited toward the end of the concentric tubes from which argon gas is issuing, the plasma appears as a pale-blue-to-lilac flame coming out of the end of the tube, which is why the system is referred to as a torch, as in a welding torch. 

Hot Work. The objective of a hot work standard is to prevent fires, explosions, and other causes of injury which might result from workplace ignition sources such as welding (qv), cutting, grinding, and use of electrically powered tools. The OSHA standards have specific requirements (36,94) for fire prevention and protection and a permit system. 

In those instanees when objeets to be welded or eut eannot be moved and all Are hazards eannot be removed, are speeial preeautions taken to proteet eombustibles from ignition sourees [OSHA Referenee. 252(a)(2)]... 

A reactor was prepared for maintenance and washed out. No welding needed to be done, and no entry was required, so it was decided not to slip-plate off the reactor but to rely on valve isolations. Some flammable vapor leaked through the closed valves into the reactor and was ignited by a high-speed abrasive wheel, which was being used to cut through one of the pipelines attached to the vessel. The reactor head was blown off and killed two men. It was estimated that 7 kg of hydrocarbon vapor could have caused the explosion. 

It is believed that the vapor was ignited by welding near an open vent. The body of the welder was found 100 ft up on the top of a neighboring gasholder, still holding a welding toreh. 

Tanks containing liquefied gases that are kept liquid by refrigeration sometimes have electric heaters beneath their bases to prevent freezing of the ground. When such a heater on a liquefied propylene tank failed, the tank became distorted and leaked—but fortunately, the leak did not ignite. Failure of the heater should activate an alarm. As stated in Section 5.2, frequent complete emptying of a tank can weaken the base/wall weld. 

A leak in another heat exchanger allowed flammable gas to enter a cooling-water return line. The gas was ignited by welding, which was being carried out on the cooling tower. The atmosphere had been tested before work started, five hours earlier (see Section 1.3.2). 

Though the tank had been cleaned, traces of heavy oil were stuck to the sides or behind rust or trapped between plates. These traces of oil were vaporized by the welding and ignited. 

An unusual case of an explosion in a vessel containing traces of heavy oil occurred when welding was carried out on the brakes of a tractor. The heat vaporized and ignited the lubricant used in fitting the tires, and the resulting explosion killed three men. 

Water v. as being drained from a tank on another part of the plant. The v. ater flow was too great for the capacity of the drains, so the water backed up into the compound of small tanks, taking some light oil with it. This oil was ignited by welding sparks. 

An intimately powdered mixture, usually ignited by magnesium ribbon as a high-temperature fuse, reacts with an intense exotherm to produce molten iron and was used formerly (before the advent of gas or arc welding) in the commercial thermite welding process. Incendive particles have been produced by this reaction on impact between aluminium and rusty iron. (The term thermite reaction has now been extended to include many combinations of reducing metals and metal oxides) [1], Some accidents in demonstrating the thermite reaction are described [2],... 

The foreman recognized a possible hazard from flammable vapor escaping from the vent pipe and igniting on the sparks from the welding operation. He connected a hose to the vent at the top of the tank and ran the hose down to the ground. Because the flammable vapors were water soluble, he stuck the end of the hose in a drum full of water. During a subsequent operation that involved emptying the tank, an accident occurred. Can you explain what happened and how ... 

Leaking pump released fuel oil which was ignited by nearby welding and spread to other tanks. 4,300,000 loss... 

Circumferencial weld crack leaded propane which ignited resulting in a vapor cloud. Resulting explosion and fires severely damaged facility. 

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