The flammability of these materials is variable. The low-molecular-weight materials (gases and liquids) are generally dangerously flammable. However, many halogenated organic compounds of high molecular weight, in particular those containing several halogen atoms per molecule, are nonflammable; some are in fact used as fire retardants.

Halogenated aliphatic compounds are moderately or very reactive. They generally become less reactive as more of their hydrogen atoms are replaced with halogen atoms. Halogenated acetylene compounds are unstable and should be treated as explosives. Low molecular weight haloalkanes are highly flammable and can react with some metals to form dangerous products. They are also peroxidizable and may polymerize violently. They may react violently with aluminum. Materials in this group are incompatible with strong oxidizing and reducing agents. Also, they are incompatible with many amines, nitrides, azo/diazo compounds, alkali metals, and epoxides.

Many halogenated hydrocarbons have moderate to high toxicity by inhalation. The brominated materials tend to be particularly toxic. Much of the toxicity is due to the fact that these substances are not metabolized, but persist and accumulate in fatty tissues (they tend to be fat-soluble). The combustion of chlorinated organic compounds may produce poisonous phosgene gas (COCl2). Other materials formed by incomplete combustion are classes of chlorinated organic compounds, chlorodibenzodioxins and chlorodibenzofurans. These compounds cause cancer in laboratory tests.

Alkyl halides include carbon bonded to chlorine, bromine, and iodide. Fluorocarbons are handled in a different group. Carbons with double bonds are included while aromatics are handled in Group 66 (Aryl Halides). This class of compounds is extremely important in industry in the production of polymers, pesticides, and fire retardants.

1-chloro-2-bromoethane, benzyl bromide, captan, vinyl chloride, vinylidene chloride, methylene chloride, chloroform, iodoacetic acid, mustard gas, carbon tetrachloride.