Sources of ignition

Autoignition temperature. The autoignition temperature of a material is the temperature at which it will ignite spontaneously in air without any external source of ignition. 

Combustion of a flammable gas-air mixture occurs if the composition of the mixture lies in the flammable range and if there is a source of ignition. Alternatively, combustion of the mixture occurs without a source of ignition if the mixture is heated up to its autoignition temperature. 

While with-in the mobile x-ray system, the waste in the sampler, is contained within a replaceable (and disposable) polyvinyl chloride (PVC) sleeve with a wall thickness of approximately 0.2-inches and a sealed bottom. It was anticipated that the PVC tube or sleeve would, with use, become highly contaminated with waste residues which drip of fall-off the sampler. The sleeve is coated with a conductive coating to prevent static electricity buildup . There are no sources of ignition in this sealed spare. The sampler (and waste) is coupling which includes a positive pressure gasket. This barrier is further isolated by a second barrier consisting of an epoxy coated aluminum sleeve also sealed-off from the main x-ray cabinet and PVC sleeve. There are also no potential sources of ignition in this isolated secondary space as well. 

The relatively low flash points of some acrylates create a fire hazard. Also, the ease of polymerization must be home in mind in ah. operations. The lower and upper explosive limits for methyl acrylate are 2.8 and 25 vol %, respectively. Corresponding limits for ethyl acrylate are 1.8 vol % and saturation, respectively. All possible sources of ignition of monomers must be eliininated. 

Acrylonitrile is combustible and ignites readily, producing toxic combustion products such as hydrogen cyanide, nitrogen oxides, and carbon monoxide. It forms explosive mixtures with air and must be handled in weU-ventilated areas and kept away from any source of ignition, since the vapor can spread to distant ignition sources and flash back. 

Burning. Acryhcs form a black bead that is easily cmshed in the fingers. There is usually no smell of acetic acid as with ceUulose acetate. Many of the modacryhcs, such as Dynel, do not form a bead in this test. In general the modacryhcs do not support combustion when removed from the source of ignition. 

Thermoplastic Fibers. The thermoplastic fibers, eg, polyester and nylon, are considered less flammable than natural fibers. They possess a relatively low melting point furthermore, the melt drips rather than remaining to propagate the flame when the source of ignition is removed. Most common synthetic fibers have low melting points. Reported values for polyester and nylon are 255—290°C and 210—260°C, respectively. 

Fire-Resistant Hydraulic Fluids. Fire-resistant hydrauhc fluids are used where the fluid could spray or drip from a break or leak onto a source of ignition, eg, a pot of molten metal or a gas flame (17). Conditions such as these exist in die-casting machines or in presses located near furnaces. Specific tests for fire resistance are conducted by Factory Mutual in the United States. 

Alkylamiaes are toxic. Both the Hquids and vapors can cause severe irritations to mucous membranes, eyes, and skin. Protective butyl mbber gloves, aprons, chemical face shields, and self-contained breathing apparatus should be used by aH personnel handling alkylamiaes. Amines are flammable and the lower mol wt alkylamiaes with high vapor pressures at ordiaary temperatures have low flash poiats. Amines should be handled ia weH-veatilated areas only after eliminating potential sources of ignition. 

Manufacturers of benzene are requited by federal law to pubHsh Material Safety Data Sheets (MSDS) that describe in detail the procedures for its safe handling. Benzene is classified as a flammable Hquid and should be stored away from any potential source of ignition. Fine and explosion hazard data for benzene are shown (91). 

Methyl bromide is nonflammable over a wide range of concentrations in air at atmospheric pressure and offers practically no fire hazard. With an intense source of ignition, flame propagation within a narrow range from 13.5 to 14.5% by volume has been reported. The material has no flash point. Thermal decomposition in a glass vessel begins somewhat above 400°C. 

The carbonates should be plainly labeled and stored in cool, dry areas away from sources of ignition. The U.S. Department of Transportation (DOT) Hazardous Materials Regulations control the shipment of carbonates as described in Table 8. 

If the density of a vapor is greater than air, as is the case with most gases and vapors encountered in industry, flammable concentrations may collect at low levels, such as at floor level or in basements, and can travel considerable distances to a source of ignition and the flames will then flash back. 

Elash point The lowest temperature at which vapors above a volatile combustible substance ignite in air when exposed to a source of ignition. 

Stray Electrical Currents and Induced Radio Frequency Currents. For information on stray currents see API 2003 [3j. For information on both hazards see the author s review Sources of Ignition in [157]. Electrostatic Discharge (ESD) Damage to Electronic Equipment. Marine Tankers and Barges (see [5] ISGOTT ). 

In order for static electricity to be a source of ignition, four conditions must be fulfilled... 

It is recommended that flammability always be assessed first, since it is inherently safer to avoid flammable atmospheres than to avoid sources of ignition such as static electricity. If a flammable atmosphere cannot be avoided at all times, the system should be designed to minimize both the probability and consequences of ignition. In this chapter it is assumed that static electricity is the only source of ignition however, in practical situations all sources of ignition such as those described in [ 157] should be evaluated. 

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