Protection against Toxic Gases

For protection against toxic gases, activated carbon is supplied in granular form. Hardness of particles is essential to maintain a firmly packed bed in the canister and minimize dusting. Because of the small space available in the canister of a ga mask the adsorptive power must be concentrated in a small volume. The carbon, therefore, should be as dense as is consistent with high intrinsic adsorptive power. A rapid rate of adsorption is essential. 

Studies made at the time of World War I showed that a gas mask should be capable of reducing the concentration of a toxic gas from 1000 parts per million to I part per million or less within 0.1 second. This calculation was based on the amount of air required by a normal individual when exercising, and on the dimensions and design of the canisters then in use.5 

At the close of World War 1, a mixture of 75% carbon and 25% soda-lime was adapted for American canisters, the soda-lime 

Another benefit of soda-lime is illustrated by the behavior of phosgene. When phosgene and moisture are simultaneously adsorbed, the carbon catalyzes the reaction, whereby carbon dioxide and hydrogen chloride are formed. The resulting hydrogen chloride is not well adsorbed by carbon, but is effectively neutralized by the soda-lime. 

Active carbons accelerate reactions to which various other war gases are subject and this phase has been given much study. One development is to impregnate carbons with salts that enhance the catalytic power and destroy the toxicity of a gas by a chemical change. This provides protection against certain toxic gases that cannot be eliminated by adsorption alone.6 

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Davidson Pratt, Protection against Toxic Gases in Industry," Inst, of Ohem. Publication, 1936, p. 15. 

Phosgene (military designation, CG) appears at usual battlefield temperatures as a white cloud whose density is due, in part, to hydrolysis. The gas is heavier than air and at low concentrations has a characteristic odor of newly mown hay. At higher concentrations, a more acrid, pungent odor may be noted. An odor threshold of 1.5 ppm has been reported but does not apply to all observers. This odor threshold is inadequate to protect against toxic inhalant exposures to this substance. Furthermore, a... 

Within a few days after the Ypres attack, on the appeal of Lord Kitchener, Secretary of State for War, British women had equipped the entire British Expeditionary Forces with gauze pads which could be used as a crude mask to protect against toxics. The French provided similar pads, and, like both the British and Germans, furnished chemicals to wet the pads in order to increase their filtering potential. The development of an offensive capability in gas warfare naturally took longer. The British designated elements of the War Office to initiate... 

Phosgene is manufactured from a reaction of carbon monoxide and chlorine gas in the presence of activated charcoal. Phosgene is used in the manufacture of isocyanates, polycarbonates, pesticides, dyes, and pharmaceuticals. Manufacture of phosgene in the United States is almost entirely captive in that more than 99% is used in the manufacture of other chemicals within a plant boundary (US EPA, 2003). The odor threshold is between 0.5 and 1.5 ppm (NIOSH, 1976) unfortunately, the odor threshold is inadequate to protect against toxic inhalant exposure because damage to the deep respiratory tract can take place at lower concentrations (Sidell et al., 1997). Phosgene has an odor safety classification rating of "E," which indicates that fewer than 10% of attentive persons can detect the Threshold Limit Value (TLV) (Amoore and Hautala, 1983). 

Provide permanent brazed or welded pipelines from the cylinders to near the points of gas use. Select pipe materials suitable for the gas and its application. Any flexible piping used should be protected against physical damage. Never use rubber or plastic connections from cylinders containing toxic gases. 

Precautions also have to be instituted to protect against the inherent properties of the cylinder contents, e.g. toxic, corrosive, flammable (refer to Table 8.1). Most gases are denser than air common exceptions include acetylene, ammonia, helium, hydrogen and methane. Even these may on escape be much cooler than ambient air and therefore slump initially. Eventually the gas will rise and accumulate at high levels unless ventilated. Hydrogen and acetylene can form explosive atmospheres in this way. 

Various types of PFC-based gels and gel-emulsions have been reported [5,66,67]. They may find applications in topical drug delivery, wound healing, and implantable drug depots and as low-friction, gas-permeant, repellent protective-barrier creams against toxic or aggressive media, and in cosmetics. 

Wachtel(Ref 2) lists bromoacetone as first used in July 1915 in a war gas, called Martonite (BA 80 + chloroacetone 20%) in Ft, B-Stoff in Ger and BA in USA. This compd is a powerful lachrymator. In sprays, it causes, in contact with the skin, painful blisters, which heal within a short time. A concn of 1.5 mg/m3 causes tears immediately, 2.8 mg/m3 causes fighting inefficiency, 560 mg/m3 is toxic and 3200 mg/m3 is a lethal concn after 10 min exposure. Protection against the lachrymatory effect is possible by well-fitted goggles. Detection of BA in the field is easily made by odor irritation caused by the vapor(Ref 2)... 

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