Class I substance

The 1990 Clean Air Act regulates the production and use of CFCs, hydrochlorocarbons, hydrochlorofluorocarbons (HCFCs), and hydrofluorocarbon (HFC) substitutes. CFC and halon (Class I substances) usage is to be phased out in steps until total phaseout occurs on January 1,... 

Fig. 21.12. Principal level C in vitro/in vivo correlation for immediate-release (IR) formulation of class I substance.

Class I substances are those with stmcmres and related data suggesting a low order of oral toxicity. They have simple chemical stmctures and are efficiently metabolized by high-capacity pathways. 

Class II substances are simply intermediate substances with less clearly innocuous stmcmres than those of Class I substances, but without stmctural feamres suggestive of toxicity. 

Isopropatnlde (SK+F standard SJB- 6-226-A) melted between I89.O - 191-5°C. without decomposition under USP conditions for class I substances (g). 

Short-term genotoxicity tests, including bacterial and mammalian cell assays, are widely used to assess potential carcinogenicity of chemical and physical agents, owing to the prominent role of genetic effects in the initiation and promotion of cancer however, the predictive value of such tests is far from absolute (114). Of the carcinogens listed as class I substances, Cr(Vl)... 

Replacement compounds for CFCs are HCFCs and HBFCs. Although HBFCs were not originally regulated under the Clean Air Act, subsequent regulation added them to the list of class I substances and they were phased out in 1996 because of... 

Laboratories should also be aware of regulatory provisions relating to stratospheric-ozone-depleting substances. The list of such substances can be found at 40 CFR 82, Appendixes A and B to Subpart A. The list includes as "Class I" substances most common freons, carbon tetrachloride, and methyl chloroform. The regulations prohibit the movement in interstate commerce of these substances and other listed ozone-depleting substances. 

In Step 2, constituents are assigned to one of three structural classes (I, II, or III) based on toxic potential (Cramer et al., 1978). Class I substances contain structural features that suggest a low order of oral toxicity. Class II substances are clearly less innocuous than Class I substances but do not contain structural features that provide a positive indication of toxicity. Class III substances contain structural features (e.g., an epoxide functional group, unsubstituted heteroaromatic derivatives) that permit no strong presumption of safety and in some cases may even suggest signi cant toxicity. For instance, the simple aliphatic hydrocarbon, limonene, is assigned to structural Class I, while... 

Class II. Chemicals of intermediate concern that are less innocuous than Class I substances but lack the positive indicators of toxicity that are characteristic of Class in chemicals. 

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