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Study of the effect of atmospheric relative humity (RH) on the adsorption of paraformaldehyde-generated formaldehyde gas on various surfaces and the effect of the adsorbed formaldehyde on the death rate of bacterial spores showed that increasing the RH caused a corresponding increase of formaldehyde levels on all surfaces. The amount peaked at 83% RH. The levels obtained at 100% RH were slightly below those at 83% RH. Cotton cloth had a much greater affinity for the gas at all RH than either glass or stainless steel. The death rate of bacterial spores on surfaces containing adsorbed formaldehyde was high for the first hour after removal from the formaldehyde atmosphere but decreased rapidly thereafter. This held true for both cotton and glass surfaces. Also, formaldehyde levels of 15 to 27 mg/ml of nutrient broth caused inhibition of bacterial growth, but levels above 27 gg/ml rendered broth sterile.

The effect of relative humidity (RH) on formaldehyde penetration of paper, glassine, and cotton was determined by the death rate of bacterial spores in glass tubes covered with these materials. The data show that paper is readily penetrated regardless of RH, but the RH greatly affects the penetration rate of glassine and cotton. A comparison was also made of the effect of RH on the penetrability of formaldehyde generated from Formalin and paraformaldehyde. At low RH, all three closures were penetrated more readily by formaldehyde from paraformaldehyde than from Formalin, but no difference in the two was observed at high RH. It is felt that the difference at low RH is primarily due to the condensation of the vaporized Formalin.

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