Class II chemicals

In addition, EPA must ensure that Class I chemicals be phased out on a schedule similar to that specified in the Montreal Protocol—CFCs, halons, and carbon tetrachloride by 2000 methyl chloroform by 2002—but with more stringent interim reductions. Class II chemicals (HCFCs) will be phased out by 2030. Regulations for Class I chemicals will be required within 10 months, and Class II chemical regulations will be required by December 31, 1999. 

The law requires nonessential products releasing Class 1 chemicals to be banned within 2 years of enactment. In 1994 a ban wiU go into effect for aerosols and non-insulating foam using Class II chemicals, with exemptions for flammability and safety. Regulations for this purpose will be required within one year of enactment, to become effective tv o vears afterwards. 

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. 

G. Cla57ton and F. Cla57ton, eds., Patty s Industrial Hygiene andToxicology, 3rd ed., Vol. 2A, John Wdey Sons, Inc., New York, 1981, pp. 2089—2091. "Aryl Sulfonic Acids and Salts," Information Profiles on Potential Occupational Hayards, Vol. II, Chemical Classes, Center for Chemical Hazard Assessment, Syracuse Research Corp., U.S. Dept, of Commerce, Washington, D.C., 1979. 

The law also requires EPA to publish a list of safe and unsafe substitutes for Class I and II chemicals and to ban the use of unsafe substitutes. 

NFPA-325 Guide to Fire Hazard Properties of Flammable Liquids, Gases and Volatile Solids, (1994 ed.), NFPA-321 Basic Classification of Flammable and Combustible Liquids (1991 ed.), NFPA-497A, Classification of Class 1 Hazardous (Classified) Locations for Electrical Installations in Chemical Process Areas (1992 ed.), and NFPA-497B, Classification of Class II Hazardous (Classified) Locations for Electrical Installations in Chemical Process Areas (1991 ed.), National Fire Protection Association, Quincy, MA. 

Minerals generally present difficult problems in chemical analysis, and these problems grow more serious when the elements being determined are as difficult to separate as are those named above. The time and effort that x-ray emission spectrography can save are therefore great, but there are obstacles to be surmounted. Among these are (1) Absorption and enhancement effects are often serious. (2) The element of interest may be present at low concentration in a matrix that is unknown and variable. (3) Satisfactory standards are not always easy to obtain. (4) Simple equipment sometimes does not resolve important analytical lines- completely. (5) Sample preparation and particle size often influence the intensities of analytical lines Class II deviations (7.8) can be particularly serious with minerals. 

Class II dependence for the activation of a chemical bond as a function of surface metal atom coordinative unsaturation is typically found for chemical bonds of a character, such as the CH or C-C bond in an alkane. Activation of such bonds usually occurs atop of a metal atom. The transition-state configuration for methane on a Ru surface illustrates this (Figure 1.13). 

According to the literature [21], all reported electrochemical oscillations can be classified into four classes depending on the roles of the true electrode potential (or Helmholtz-layer potential, E). Electrochemical oscillations in which E plays no essential role and remains essentially constant are known as strictly potentiostatic (Class I) oscillations, which can be regarded as chemical oscillations containing electrochemical reactions. Electrochemical oscillations in which E is involved as an essential variable but not as the autocatalytic variable are known as S-NDR (Class II) oscillations, which arise from an S-shaped negative differential resistance (S-NDR) in the current density (/) versus E curve. Oscillations in which E is the autocatalytic variable are knovm as N-NDR (Class III) oscillations, which have an N-shaped NDR. Oscillations in which the N-NDR is obscured by a current increase from another process are knovm as hidden N-NDR (HN-NDR Class IV) oscillations. It is known that N-NDR oscillations are purely current oscillations, whereas HN-NDR oscillations occur in both current and potential. The HN-NDR oscillations can be further divided into three or four subcategories, depending on how the NDR is hidden. 

Famphur is considered a Class II toxic compound to the Japanese quail (Cotumix japonica) according to the classification of Hill and Camardese (1986). Class II compounds (very toxic) kill 50% of the test organisms on diets containing 40 to 200 mg chemical/kg ration for 5 days followed by a 3-day observation. By comparison, the 50% kill in other classes (in mg/kg diet) is <40 in Class I (highly toxic), >200 to 1000 in Class III (moderately toxic), >1000 to <5000 in Class IV (slightly toxic), and >5000 in Class V (practically nontoxic) (Hill and Camardese 1986). Smith (1987) rates famphur as a Class I toxic compound, as judged by results of dietary tests with mallards. 

National Fire Protection Association (NFPA), NFPA 497B. Classification of Class II Hazardous Locations for Electrical Installations in Chemical Process Areas. NFPA, Quincy, MA, 1991. 

Scheme 6.1 Chemical structures of adrenergic receptor antagonists for generation of antitarget pharmacophores class I (a) and class II (b).

In the case of class-II inhibitors, the acyl-enzyme undergoes either normal deacylation (Fig. 5.3, Pathway c) or a chemical re-arrangement in which the enamine tautomerizes to an imine, generating an acyl-enzyme with a A -pyrroline structure (Fig. 5.3, Pathway b). This second acyl-enzyme intermediate hydrolyzes at a much slower rate, and the decreased tum°ver cacis t0 transient inhibition of the enzyme [22] [50]. 

SEA (Leu-48-Gly) and SEB (Phe-44-Ser) mutants unable to bind major histocompatibility complex class II remain emetic but lack T-cell mitogenic effects. " A disulfide loop in SEs, which is absent in the non-enterotoxic TSST-1, may be responsible for the emetic activity of SEs but that too remains controversial. Carboxymethylation of histidines on SEA or SEB generates superantigenic molecules devoid of enter-otoxicity or skin reactivity. This chemically modified SEB also inhibits, perhaps in a competitive fashion, the... 

Cumulative distributions of the logarithms of NOELs were plotted separately for each of the stmcmral classes. The 5th percentile NOEL was estimated for each stmctural class and this was in mrn converted to a human exposure threshold by applying the conventional default safety factor of 100 (Section 5.2.1). The stmcmre-based, tiered TTC values established were 1800 p,g/person/ day (Class I), 540 pg/person/day (Class II), and 90 pg/person/day (Class III). Endpoints covered include systemic toxicity except mutagenicity and carcinogenicity. Later work increased the number of chemicals in the database from 613 to 900 without altering the cumulative distributions of NOELs (Barlow 2005). 

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