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544 G. W. JONES HAZARDS OF COMBUSTIBLE GASES AND VAPORS 545 I! Most of the sources of ignition given above can be controlled by establishing Methane is highly flammable in air when the concentrations are within tfe pper safety regulations and installing flameproof and vaporproof electrical limits given above. Methyl chloride does not produce as violent explosions af fjpment; others, by designing the plants so that boilers, water heaters, in- certain methane-air mixtures, yet explosions of this combustible in air may c| ifierators, and other equipment where there are open flames and incandescent considerable damage. Methylene chloride is entirely safe when mixed with ail Aerials are installed in other buildings at a safe distance from the place where at ordinary temperatures and pressures, but it is flammable in air at elevate cesses involving explosion hazards are carried out. temperatures, and, when mixed with pure oxygen in the right proportions, forSi 1 Static electricity has caused many serious fires and explosions and is one of highly explosive mixtures. Chloroform has no explosive properties, while carboi most difficult ignition hazards to control. There are few operations in which it tetrachloride is entirely nonflammable with air or oxygen in any proportions^ iy not be present. It is more serious in dry atmospheres where the relative temperatures and, in fact, is used to good advantage in the preparation of noffi .idity is below 50 per cent. Static electricity may be generated by friction, that combustible, nonflammable dry-cleaning compounds. By the addition of the prope; |>y slipping belts, pulleys, and revolving machinery, and by passage of solids, proportions of CCU to combustible liquids, such as naphtha and petroleui ids, or gases at high velocity through small openings. It also may be generated distillates, the resulting mixtures are rendered incombustible and nonflammab .^impact, pressure, cleavage, and induction. It may be partly, or totally elimi- However, when these liquid mixtures evaporate, unless the vapor pressure.^ fed'by the proper grounding of all machinery, pipes, and other equipment where the combustible portion is as great as that of carbon tetrachloride, flammal arges may accumulate. Whenever practical there is added safety in also main liquid mixtures may remain. At least one serious explosion is known to ha1 taining the room humidity above 50 per cent. occurred from such a mixture. Conversely, should the combustible portion ha| a vapor pressure greater than that of carbon tetrachloride, the liquid residue woul E. SEGREGATION OF HAZARDOUS OPERATIONS remain nonflammable, but flammable vapor-air mixtures could be formed frif its evaporation. Trichloroethylene and various Freon compounds may be used to advanfa where liquids having nonflammable characteristics are required. Operations that, through necessity rather than choice, require the use of jge volumes of flammable gases or vapors should be segregated from other fiations. This requires installation of hazardous processes in buildings at a safe ill|ance, and, if heavy combustible vapors are involved, the elevation should be D. ELIMINATION OF IGNITION SOURCES Combustible gases and vapors, mixed with air or pure oxygen in proportion to give flammable mixtures, may be employed safely provided all 60urc?|| ignition are eliminated. The atmosphere in the gasoline tanks of the milliong automobiles and trucks in use on our streets and highways contains "dit! flammable'mixtures or mixtures that become flammable when air is added,-y<jj>l number of accidents caused by these conditions is extremely small. TJtn| largely because the tanks are kept closed, the mixtures inside the tankfl usually above the upper limit of flammability, and no sources of igmticmfflg present in the tank or around the filler cap. .*3 The safety engineer is primarily interested in the sources of ignition that-raayjj ..cause_explosions_.These_sources-may_be_classifiad..as_gi.ven-belowL:_______ Flames (Open lights -M Matches and cigarette lighters Fires in boilers and water heaters [Burning material; incinerators `` Ignition sources Sparks Static electricity Electrical shorts and arcs Lightning Sparks from tools qw that of other buildings, so that in case of a fire or explosion the liquids ipspors'tha'rmaybeTelea'sed'wiH-not -flow- toward~other adj acent- buildings. fl|les of safe distance for various operations involving the use of combustible ids and vapors have not been developed adequately, as has been done in the inufacture and storage of explosives. Therefore, it becomes the duty of the |pty engineer to use his own judgment as to what distance is safe for a given juration. F. PROVISION OF ADEQUATE VENTILATION The necessity for adequate ventilation where flammable gases and vapors e^,handled and used cannot be too strongly emphasized...This need for adequate 'tilation applies not only to the spaces around the equipment in which the ^ma^b-'e-prKentV'but slstrto-all-conduite; trenchesrand- tunnels where-pipes "conveying flammable gases and vapors and pipelines for conveying flammable uids are installed. Such lines should be carried in the open air from one building ^another, and in buildings they should be suspended above the floor level where Key-can be .inspected readilv for-leaks.____________ . _______ -____________ The buildings should be of light material that will not offer too great ittance to applied pressure if an explosion occurs. The roofs should be provided ith ventilators, and windows should be installed with tilting-type sashes that en when pressure is exerted from the inside. A reduction of pressure on the Heated materials Glowing metals; hot cinders Overheated bearings Electric light filaments Spontaneous combustion