• LC5O: (Lethal Concentration 50) is the concentration of a chemical which kills 50% of a sample population. This measure is generally used when exposure to a chemical is through the animal breathing it in, while the LD5O is the measure generally used when exposure is by swallowing, through skin contact, or by injection. (See also LD5O).

• LD5O: (Lethal Dose 50) is the dose of a chemical which kills 50% of a sample population. In full reporting, the dose, treatment and observation period should be given. Further, LD5O, LC5O, ED5O and similar figures are strictly only comparable when the age, sex and nutritional state of the animals is specified. Nevertheless, such values are widely reported and used as an effective measure of the potential toxicity of chemicals. (See also LC5O).

• LDLO: Lethal Dose Low.

• PEL: Permissible Exposure Limit is a time-weighted average (TWA) or absolute value (usually prescribed by regulation) setting out the maximum permitted exposure to a hazardous chemical.

• OEL (Occupational Exposure Limit) A (generally legally-enforcable) limit on the amount or concentration of a chemical to which workers may be exposed.

• TLV (Threshold Limit Value) is the maximum permissible concentration of a material, generally expressed in parts per million in air for some defined period of time (often 8 hours). These values, which may differ from country to country, are often backed up by regulation and therefore may be legally enforceable.

• TWA (Time Weighted Average) This term is used in the specification of Occupational Exposure Limits (OELs) to define the average concentration of a chemical to which it is permissible to expose a worker over a period of time, typically 8 hours.

1. OSHA is the (USA) Occupational Safety and Health Administration, which adopts and enforces health and safety standards.

2. The CAS Registry number is a unique number assigned to a chemical by the Chemical Abstracts Service

3. The ACGIH is the American Conference of Governmental Industrial Hygienists. One of its principal tasks is to recommend TLVs for workplace exposure to chemicals.

4. COSHH (the Control of Substances Hazardous to Health). The COSHH regulations impose a number of obligations on employers; the object of the regulations is to promote safe working with potentially hazardous chemicals.

5. A Carcinogen is a chemical known or believed to cause cancer in humans. The number of proven carcinogens is comparatively small, but many more chemicals are suspected to be carcinogenic. A partial list of known and suspected carcinogens is held at: -

http://physchem.ox.ac.uk/MSDS/carcinogens.html