as defined by ACGIH, concentration to which it is believed that workers can be exposed continuously for a short period of time without suffering from (1) irritation, (2) chronic or irreversible tissue damage, or (3) narcosis of sufficient degree to increase the likelihood of accidental injury, kahjuliku aine piirkontsentratsioon, mida peetakse teatud lühiajalise mõju korral töötajatele üldiselt ohutuks