TAR

Tar is a thick, dark, viscous liquid obtained from the destructive distillation of organic materials such as coal or wood. It is a complex mixture of hydrocarbons and other organic compounds. Coal tar is produced during coal processing and coking; wood tar is obtained by pyrolysis of wood. Tar is distinct from bitumen, which is petroleum-derived.

In terms of composition, tar contains polycyclic aromatic hydrocarbons (PAHs), phenols, cresols, and heterocyclic compounds. Its physical form varies with temperature and composition; it is sticky at room temperature and can emit vapors when heated. Different tars are refined for specific uses.

Historical uses include waterproofing, roof coatings, and ship caulking, as well as protective coatings for wood and stone. In road construction, tar was a common binder in early asphalt; modern roads tend to use bitumen derived from crude oil, with tar used less frequently due to health concerns.

Health and safety: Tar contains carcinogenic PAHs and other toxic compounds. Exposure can occur via inhalation of fumes or skin contact and has been linked to cancer and skin disorders in occupational settings. Protective equipment and proper ventilation are used to mitigate risks; disposal and remediation require care to prevent contamination.

Environmental and historical notes: Tar production has influenced industry and urban development, from lighthouse preservation to roofing traditions. Pine tar, tar from pine trees, and other wood tars have antimicrobial properties and have been used in preserving vessels and wood. Tar's associations with weatherproofing and waterproofing are longstanding.

See also: tar (Unix) is a widely used archiving program.