ABC of Safety in the Biological Sciences



Chemical Safety Information - Glossary

  • An acute hazard is one to which a single exposure may cause harm, but which is unlikely to lead to permanent damage.
  • Allergic contact dermatitis is a type of skin hypersensitivity. Its onset may be delayed by several days to as much as several years, for weaker sensitizers. Once sensitized, fresh exposure to the sensitizing material can trigger itching and dermatitis within a few hours.
  • The Ames Test is used to assess whether a chemical might be a carcinogen. It assumes that carcinogens possess mutagenic activity, and uses bacteria and mammalian microsomes to determine whether a chemical is a mutagen. Approximately 85% of known carcinogens are mutagens. The Ames test, therefore, is a helpful but not perfect predictor of carcinogenic potential.
  • Argyria or argyrism is an irreversible blueish-black discolouration of the skin, mucous membranes or internal organs caused by ingestion of, or contact with, various silver compounds.
  • The auto-ignition temperature of a chemical is the lowest temperature at which the material will ignite without an external source of ignition.
  • The breakthrough time is the time taken in standard tests for permeation of a chemical through a protective barrier (such as a rubber glove) to be detected.
  • A carcinogen is a chemical known or believed to cause cancer in humans. The number of known carcinogens is comparatively small, but many more chemicals are suspected to be carcinogenic. A partial list of known and suspected carcinogens is held at
  • The CAS Registry number is a unique number assigned to a chemical; by the Chemical Abstracts Service.
  • A chronic hazard is a chemical which has the potential to cause long-term damage to health, often as a consequence of repeated or prolonged exposure to it.
  • Chrysiasis is the development of a blue-grey pigmentation in skin and mucous membranes. May be caused by exposure to gold compounds.
  • 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.
  • A cutaneous hazard is a chemical which may cause harm to the skin, such as defatting, irritation, skin rashes or dermatitis.
  • ED50: (Effective Dose 50) is the amount of material required to produce a specified effect in 50% of an animal population. (See qualification in the definition of LD50).
  • Embryotoxins retard the growth or affect the development of the unborn child. In serious cases they can cause deformities or death. Mercury compounds and certain heavy metals, aflatoxin, formamide and radiation are known embryotoxins.
  • Etiologic agents: microscopic organisms such as bacteria or viruses, which can cause disease.
  • The flash point of a chemical is the lowest temperature at which a flame will propagate through the vapour of a combustible material to the liquid surface. It should be noted that the source of ignition need not be an open flame, but could equally be, for example, the surface of a hot plate, or a steam pipe.
  • Hazard codes - see UN hazard codes.
  • A hematopoietic agent is a chemical which interfers with the blood system by decreasing the oxygen-carrying ability of haemoglobin. This can lead to cyanosis and unconsiousness. Carbon monoxide is one such agent, familiar to smokers.
  • A hepatotoxin is a chemical capable of causing liver damage.
  • HSE The Health and Safety Executive. The HSE web site can be reached through The HSE is responsible for proposing and enforcing safety regulations throughout UK industry and academia. Publications are available on a wide variety of safety-related issues.
  • Hypoxia is a condition defined by a low supply of oxygen.
  • IARC International Agency for Research in Cancer. The IARC home page is at
  • IOSH Institute for Occupational Safety and Health. IOSH has its home page at
  • An Irritant is a chemical which may cause reversible inflammation on contact.
  • LC50: (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 LD50 is the measure generally used when exposure is by swallowing, through skin contact, or by injection. (See also LD50).
  • LD50: (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, LD50, LC50, ED50 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 LC50).
  • LDLO Lethal Dose Low.
  • Median Lethal Dose (MDL): see LD50.
  • The MEL (Maximum Exposure Limit) is the maximum permitted concentration of a chemical to which a worker may be exposed over an extended period of time. Typically, MELs are quoted in ppm for an 8-hour reference period, though shorter periods may be quoted for some materials. MELs are, in many countries, enforceable by law. A list of chemicals for which MELs are defined in the UK is held at
  • A mutagen is an agent that changes the hereditary genetic material which is a part of every living cell. Such a mutation is probably an early step in the sequence of events that ultimately leads to the development of cancer.
  • NIOSH National Institute for Occupational Safety and Health. The NIOSH home page is at
  • A Nephrotoxin is a chemical which may cause kidney damage. Common examples include antimony compounds, dimethyl sulphoxide, dimethylformamide and tetrahydrofuran.
  • A Neurotoxin is a chemical whose primary action is on the CNS (Central Nervous System). Many neurotoxins, such as some mercury compounds, are highly toxic, and must only be used unbder carefully-controlled conditions.
  • OEL (Occupational Exposure Limit) A (generally legally-enforcable) limit on the amount or concentration of a chemical to which workers may be exposed.
  • PEL: Permissible Exposure Limit.
  • Peroxidizable materials can form peroxides in storage, generally when in contact with the air. These peroxides present their most serious risk when the peroxide-contaminated material is heated or distilled, but they may also be sensitive to mechanical shock. The quantity of peroxides in a sample may be determined using a simple peroxide test strip.
  • Photoallergic contact dermatitis is a skin condition brought on by exposure to light following skin contact with certain types of chemicals, such as sulphonamides.
  • PPM parts per million.
  • Pyrophoric materials ignite spontaneously in air. Since a wide variety of chemicals will burn if heated sufficiently, it is usual to define a pyrophoric material as one which will ignite spontaneously at temperatures below about 45 C.
  • A reproductive toxin, such as vinyl chloride or PCBs, is a chemical which may cause birth defects or sterility.
  • Risk phrases, coded in the form R34, R61 etc are now included in MSDS sheets for chemicals purchased in the UK. A list of the meaning of these codes is available at
  • A substance's RTECS number is an identification number set by the US Registry of Toxic Effects of Chemical Substances. For further information, connect to the RTECS home page at
  • A Sensitizer is a chemical which may lead to the development of allergic reactions after repeated exposure.
  • STEL (Short Term Exposure Limit) is the maximum permissible concentration of a material, generally expressed in ppm in air, for a defined short period of time (typically 5 minutes). These values, which may differ from country to country, are often backed up by regulation and therefore may be legally enforceable.
  • Systemic poisons have an effect which is remote from the site of entry into the body.
  • A teratogen is a chemical which may cause genetic mutations or malformations in the developing foetus.
  • 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.
  • TSCA Acronym for Toxic Substances Control Act.
  • 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.
  • UN Hazard codes
    • Class 1 Explosive
    • Class 2 Gases
    • Class 3.1 Flammable liquids, flash point below -18C
    • Class 3.2 Flammable liquids, flash point between -18C and 23C
    • Class 3.3 Flammable liquids, flash point between 23C and 61C
    • Class 4.1 Flammable solids
    • Class 5.1 Oxidizing agents
    • Class 5.2 Organic peroxides
    • Class 6.1 Poisonous substances
    • Class 7 Radioactive substances
    • Class 8 Corrosive substances
    • Class 9 Miscellaneous dangerous substances
    • NR Non-regulated
  • A vesicant is a chemical which, if it can escape from the vein, causes extensive tissue damage, with vesicle formation or blistering.
  • VOCs Volatile Organic Compounds.



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