nerves outside the central nervous system. Peripheral neurotoxins Substances that result in damage to nerves. In the occupational environment, these include metals such as lead, mercury and arsenic; organic solvents such as n-hexane, carbon disulphide and trichloroethylene; pesticides such as organophosphates; and other substances such as acrylamide. Peritoneum The membrane lining the abdominal cavity. It is derived from the same type of embryological tissue as the pleura. Permanent gas A gas that has a critical temperature at or below 0C, where critical temperature is the temperature above which the gas cannot be liquefied by increasing the pressure. Permit A written order giving permission to act, especially for entry into a place. Permit to work (1) Specifies details of the location and type of work to be done, confirms that identified hazards have been evaluated, and specifies the necessary protective measures. (2) See Written authority. Persistence The quality of remaining for a long period of time (such as in the environment or the body). Persistent chemicals (such as DDT and PCBs) are not easily broken down. Persistent organic pollutant (POP) (a) Means a substance listed in Schedule 2A [HSNO Act] and (b) includes a substance containing one or more of those substances; but (c) does not include a substance occurring in quantities as unintentional trace contaminants in products and articles. A person who has been offered, and accepted, work as an employee; and 'intended work' has a corresponding meaning. Person-years The number of years that a person in a study population