safety valve

safety valve (plural safety valves)

1. A relief valve set to open at a pressure below that at which a container (such as a boiler) would burst.
   • 1941 April, “British Locomotive Developments”, in Railway Magazine, page 173:

     Spun glass mattresses are used for lagging the boiler, which has three Ross pop safety valves on the front ring.

   • 1959 April, Cecil J. Allen, “Locomotive Running Past and Present”, in Trains Illustrated, page 185:

     [...] and to show that there was no shortage of steam, Royal Scot, directly we stopped, blew off vigorously from its safety-valves steam that well might have been used in the cylinders in the interest of timekeeping.

2. (figurative) Any mechanism offering relief from pressure or tension, e.g. emotionally.

   Synonyms: outlet, release

   1. (US, law) A United States law, codified at 18 USC §3553(f), authorizing a judge to disregard mandatory minimum sentences for some criminals with few or no prior offenses.
      • 2020 June 30, David Jeremiah Barron writing for the First Circuit Court of Appeals in case 19-1123:

        Hernández additionally requested that he be given a two-level safety-valve reduction pursuant to U.S.S.G. § 5C1.2, which mitigates the harsh effect of mandatory minimum sentences on certain first-time offenders who played only supporting roles in drug-trafficking schemes and who provided testimony about their involvement in the criminal activity.