safety valve
    n 1: a valve in a container in which pressure can build up (as a
         steam boiler); it opens automatically when the pressure
         reaches a dangerous level [syn: safety valve, relief
         valve, escape valve, escape cock, escape]

Safety chain \Safety chain\
   (a) (Railroads) A normally slack chain for preventing
       excessive movement between a truck and a car body in
       sluing.
   (b) An auxiliary watch chain, secured to the clothes, usually
       out of sight, to prevent stealing of the watch.
   (c) A chain of sheet metal links with an elongated hole
       through each broad end, made up by doubling the first
       link on itself, slipping the next link through and
       doubling, and so on.
       [Webster 1913 Suppl.]

   Safety arch (Arch.), a discharging arch. See under
      Discharge, v. t.

   Safety belt, a belt made of some buoyant material, or which
      is capable of being inflated, so as to enable a person to
      float in water; a life preserver.

   Safety buoy, a buoy to enable a person to float in water; a
      safety belt.

   Safety cage (Mach.), a cage for an elevator or mine lift,
      having appliances to prevent it from dropping if the
      lifting rope should break.

   Safety lamp. (Mining) See under Lamp.

   Safety match, a match which can be ignited only on a
      surface specially prepared for the purpose.

   Safety pin, a pin made in the form of a clasp, with a guard
      covering its point so that it will not prick the wearer.
      

   Safety plug. See Fusible plug, under Fusible.

   Safety switch. See Switch.

   Safety touchdown (Football), the act or result of a
      player's touching to the ground behind his own goal line a
      ball which received its last impulse from a man on his own
      side; -- distinguished from touchback. See Touchdown.
      Same as safety

   Safety tube (Chem.), a tube to prevent explosion, or to
      control delivery of gases by an automatic valvular
      connection with the outer air; especially, a bent funnel
      tube with bulbs for adding those reagents which produce
      unpleasant fumes or violent effervescence.

   Safety valve, a valve which is held shut by a spring or
      weight and opens automatically to permit the escape of
      steam, or confined gas, water, etc., from a boiler, or
      other vessel, when the pressure becomes too great for
      safety; also, sometimes, a similar valve opening inward to
      admit air to a vessel in which the pressure is less than
      that of the atmosphere, to prevent collapse.
      [1913 Webster]