Heavy Metal

Metallic elements with high atomic weights; (e.g. mercury, chromium, cadmium, arsenic, and lead); can damage living things at low concentrations and tend to accumulate in the food chain.

HEPA

Used in vacuums and air purifiers, HEPA filters are highly effective at blocking particles as small as 0.3 microns (a micron is 0.0004 inches), which can irritate airways or cause an allergic reaction. Equipment must be built to accommodate HEPA filters. They cannot be installed on non-HEPA vacuums, air purifiers and air conditioners, as air does not flow easily through them and can cause motors to burn out.

Herbicide

A chemical pesticide designed to control or destroy plants, weeds, or grasses.

Hydrocarbon

Any compound consisting only of hydrogen and carbon atoms. Petroleum consists of many different hydrocarbon compounds connected together on a “chain” . Breaking this chain apart separates these various hydrocarbon compounds for use as the basis of synthetic chemicals.

Hydrochloric Acid

(also muriatic acid)

A strong mineral or "inorganic" acid. In high concentrations, it is extremely corrosive.

Found in: Conventional toilet bowl cleaners.

Hydrogen Chloride

At room temperature, hydrogen chloride is a colorless to slightly yellow, corrosive, nonflammable gas that is heavier than air and has a strong irritating odor. On exposure to air, hydrogen chloride forms dense white corrosive vapors. Hydrogen chloride can be released from volcanoes.

Hydrogen chloride has many uses, including cleaning, pickling, electroplating metals, tanning leather, and refining and producing a wide variety of products. Hydrogen chloride can be formed during the burning of many plastics. Upon contact with water, it forms hydrochloric acid. Both hydrogen chloride and hydrochloric acid are corrosive.

Hypochlorite

(See chlorine)