Document ExJ4qnVzd9M0GQxQxvdJDwadR

FLAMMABLE AND COMBUSTIBLE LIQUIDS may at times be overemphasized, it must be recognized A summary of reports* of experimental evidence and practical experience in the petroleum industry recites that no signifi cant increase in fire safety is gained by the use of spark-resistant tools in the presence of gasoline and other hydrocarbon vapors However, some materials such as carbon disulfide, and ethyl ether have very low flash points For these, and similar materi als, the use of special tools designed to minimize the danger of sparks m hazardous locations can be recognized as a conserva tive safety measure Leather-faced, plastic, and wood tools are free from the fnction-spaik hazard Health Hazards Toxic effects Flammable liquids and their vapors may create health hazards from both surface contact and inhalation of tone vapors In flammation results from the solvent action of many flammable liquids on the natural skin oils and tissue A tone hazard of varying degree exists in practically all cases, depending on the concentration of the vapor See Chapter 40, "Elements of Indus trial Toxicology " Some flammable vapors are heavier than air and will flow into pits, tank openings, confined areas, and low places in which they contaminate the normal air and thus cause a tone atmosphere Oxygen deficiency occurs in closed containers, such as a tank which has been closed for a long time and in which rusting has consumed the oxygen AH containers should be aired and gastested before any entry Combustible gas indicators Unless tests prove otherwise, flammable and toxic mixtures should be assumed to be present in all tanks which have contained or have been exposed at any time to flam mable liquids Tests for flammable vaporair mixtures in tanks and other vessels may be made by chemical analysis of sam ples or with a combustible gas indicator A combustible gas indicator is an instru ment operating on the principle that when a mixture of flammable vapor and air is passed over a heated electric filament, the resistance of the filament will he increased in direct proportion to the amount of vapor present When resistance of this filament is balanced against the resistance of a cold filament in a Wheatstone bndge device, re sistance can be measured on a galvanometer m terms of the lower flammable limit of the mixture When combustible gas indi cators are used to test for vapors from leaded gasoline sludge, as in the bottom of storage tanks, they should be equipped with special high-temperature filaments to avoid lead contamination of the filament One type of combustible gas indicator has a meter with readings in parts of 100 per cent, which represent percentages be low the lower flammable limit of the vaporair mixtures being tested When samples of an atmosphere are drawn through the sam ple hose by the aspirator bulb, the meter will indicate whether or not the atmosphere is in the flammable range or below the lower flammable limit In the latter case, the meter will radicate the percentage of flammable vapor present--the lower flam mable limit being 100 per cent It should be remembered that a combustible gas indi cator does not indicate to the user if the concentration is within or above the flam mable range A combustible gas indicator should be used only by experienced persons, and the operator should follow the manufacturer's instructions on balancing the unit The op erator can check it by placing several drops of the flammable liquid in a small jar, shak ing it a few times to permit evaporation, and then holding the sample hose of the in strument in the mouth of the jar and press ing the aspirator bulb the required number of times If there is any question as to the indicator's accuracy, it should be returned to the manufacturer for checking With some combustible gas indicators an atmosphere may be sampled so "neb" in vapor that there is a deficiency of oxygen, so that the indicators will not give readings when samples are taken continuously The "U S Department of Commerce, Office of Technical Services Sparking Character istics and Safety Hazards of Metallic Ma terials Technical Report No NGF-T-1-57, PB 131131. 32-10