Explosion prevention .systems, flammable

Alternatives to Arresters Alternatives to the use of flame arresters include fast-ac ting isolation valves, vapor suppression systems, velocity-type devices in which gas velocity is designed to exceed flashback velocity, and control of the flammable mixture (NFPA 69 standard, Explosion Prevention Systems ). The latter alternative frequently involves reduction of oxygen concentration to less than the limiting oxygen concentration (LOC) of the gas stream. 

General measures for controlling flammable atmospheres inside equipment are described in NFPA 69 Explosion Prevention Systems. These measures do not necessarily prevent flammable atmospheres in some practical cases, such as when powders are added to an inerted vessel via an open manway. Where possible such cases are identified in the relevant sections of Chapters 5 and 6. 

Clean agent systems can also be used for explosion prevention and suppression where flammable materials are confined. Clean agent fire extinguishing systems are used primarily to protect hazards that are in enclosures or equipment enclosures. Some typical hazards that could be protected by clean agents are ... 

Waste facihties should be designed to prevent explosions in sewer systems and typically are comprised of suitable traps, vents, clean-outs, collecting chambers, etc. Flammable gas detectors are installed in sewers to warn of ha2ardous concentrations, and inert gas blanketing of closed process sumps generally is advisable. 

Flare systems are subject to potential flashback and internal explosion since flammable vapor/air mixtures may be formed in the stack or inlet piping by the entry of air, and the pilot constitutes a continuous ignition source. Flares are therefore always provided with flashback protection, which prevents a flame front from travelling back to the upstream piping and equipment. Design details are described later. 

As vent collection systems normally contain vapor/air mixtures, they are inherently unsafe. They normally operate outside the flammable range, and precautions are taken to prevent them from entering it, but it is difficult to think of everything that might go wrong. For example, an explosion occurred in a system that collected flarmnable vapor and air from the vents on a number of tanks and fed the mixture into a furnace. The system was designed to run at 10% of the lower explosion limit, but when the system was isolated in error, the vapor concentration rose. When the flow was restored, a plug of rich gas was fed into the furnace, where it mixed with air and exploded [17]. Reference 34 describes ten other incidents. 

Maintenance programs The best way to prevent fires and explosions is to stop the release of flammable materials. Preventive maintenance programs are designed to upgrade system before failures occur. 

Detonations produce much higher pressures than what be considered ordinary explosions. In most cases a process vessel or piping systems will be unable to contain detonation pressure. The only safe procedure is to avoid process system detonations is to preventing the formation of flammable vapor and air mixtures within vessels and piping systems. While the flame speed of explosions is at relatively slow speed, detonations travel at supersonic speeds and will be more destructive. 

The risk of explosion or fire associated with the use of mobile telephones in a LPG vehicle is extremely low. First, LPG vehicle fuel systems are closed systems with safety features to prevent accidental release of LPG. The risk of fuel leakage is less than that of a petrol or diesel vehicle. Second, LPG will only bum when mixed with air in proportions within the flammable limits and when there is an ignition source. Working with higher-pressure fuel systems requires special tools and... 

Isolation and containment of flammable or toxic vapors and gases within a drainage system is important to prevent their spread through the system to other locations well away from where the release or spill occurred. Isolation and containment of vapors and gases can prevent fires and explosions from propagating back to process areas or between process areas. The primary means of isolation and containment of flammable or toxic vapors and gases in drainage systems are ... 

In the prevention of industrial gas explosion disasters, the most useful terms for evaluating the hazards of various fuel/oxidant systems are believed to be limits of flammability and min spontaneous ignition temp (Ref 3)... 

The culprit turned out to be manure, all right, but of a decidedly human variety. The building s toilets connected to a septic tank, with the usual u-shaped trap built into the pipes. These traps are normally filled with water, which prevents any gas from backing up into the toilet bowl. Since septic tanks create the anaerobic conditions under which flammable methane can be generated, this is an essential safety measure. The toilets had not been used since the station was abandoned, and the water had evaporated from the plumbing system. Methane was now free to back up into the basement, and it had apparently done so. As the original investigator had proposed, a spark from the sump pump had probably set off the explosion. The bats had been falsely accused. 

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