GENERAL PROPERTIES & HEALTH EFFECTS OF SOLVENTS
A solvent is any substance—usually a liquid at room temperature—that dissolves another substance, resulting in a solution (uniformly dispersed mixture). Solvents may be classified as aqueous (water based) or organic (hydrocarbon based). Most industrial solvents are organic chemicals because most of the industrial substances they are used to dissolve are organic. Solvents are used commonly for cleaning, degreasing, thinning, and extraction.
Many solvent chemicals are also used as chemical intermediates in the manufacture and formulation of chemical products. More workers are exposed to high levels of solvents during use of the substances as cleaners and thinners and in pesticide formulations.
Hundreds of individual chemicals are used to make more than 30,000 industrial solvents. There are physical, chemical, and toxicologic properties that help to classify this large group of chemicals into families with shared or distinguishing features. These features are discussed first, followed by a brief summary of the commonly used industrial solvents according to their chemical families.
PHYSICAL & CHEMICAL PROPERTIES OF SOLVENTS
Lipid solubility is an important determinant of the efficiency of a substance as an industrial solvent and a major determinant of a number of health effects. The potency of solvents as general anesthetics and as defatting agents is directly proportionate to their lipid solubility.
Dermal absorption is related to both lipid solubility and water solubility (because the skin behaves like a lipid-water sandwich), so solvents such as dimethyl sulfoxide, dimethylformamide, and glycol ethers, which are highly soluble in both (amphipathic), are well absorbed through the skin. All organic solvents are lipid-soluble, but the extent of solubility may differ to a significant degree.
Flammability & Explosiveness
Flammability and explosiveness are the properties of a substance that allow it to burn or ignite, respectively. Some organic solvents are flammable enough to be used as fuels, whereas others (eg, halogenated hydrocarbons) are so nonflammable that they are used as fire-extinguishing agents. Flash point, ignition temperature, and flammable and explosive limits are measures of flammability and explosiveness. The National Fire Prevention Association (NFPA) rates flammability hazards by a numerical code from 0 (no hazard) to 4 (severe hazard). Table 32–1 lists flash points and NFPA codes. These properties are important to consider when selecting a solvent or substituting one solvent for another on the basis of undesirable health effects or efficacy.
Table 32–1.Industrial solvents: Properties, odor thresholds, and exposure limits. ||Download (.pdf) Table 32–1. Industrial solvents: Properties, odor thresholds, and exposure limits.
| ||Flash Point (°F) ||NFPA Flammability Codea ||Vapor Pressure (mmHg 25°C) ||Evaporation Rateb ||TLVc (ppm) ||Odor Thresholdd (ppm) ||Biologic Monitore ||General Hazards of Chemical Family and Unique Hazards of Specific Compounds |