▁is ▁always ▁consider ably ▁higher ▁than ▁the ▁operating ▁pressure ▁to ▁give ▁a ▁margin ▁for ▁safety , ▁typically ▁ 1 5 0 % ▁of ▁the ▁operating ▁pressure . ▁ ▁Bur st ▁test ▁ ▁In ▁the ▁burst ▁test , ▁a ▁vessel ▁is ▁filled ▁with ▁a ▁gas ▁and ▁tested ▁for ▁le aks . ▁The ▁test ▁pressure ▁is ▁always ▁consider ably ▁more ▁than ▁the ▁operating ▁pressure ▁to ▁give ▁a ▁margin ▁for ▁safety , ▁typically ▁ 2 0 0 % ▁or ▁more ▁of ▁the ▁operating ▁pressure . ▁ ▁Hel ium ▁leak ▁test ▁ ▁The ▁hel ium ▁leak ▁test ▁uses ▁hel ium ▁( the ▁light est ▁in ert ▁gas ) ▁as ▁a ▁trac er ▁gas ▁and ▁detect s ▁it ▁in ▁concentr ations ▁as ▁small ▁as ▁one ▁part ▁in ▁ 1 0 ▁million . ▁The ▁hel ium ▁is ▁selected ▁primarily ▁because ▁it ▁pen etr ates ▁small ▁le aks ▁readily , ▁is ▁in ert ▁and ▁will ▁not ▁react ▁with ▁the ▁test ▁piece ▁while ▁having ▁a ▁naturally ▁low ▁quantity ▁in ▁air ▁making ▁detection ▁less ▁complicated . ▁It ▁is ▁possible ▁to ▁detect ▁le aks ▁as ▁small ▁as ▁ 5 . 1 0 − 1 0 ▁Pa · m 3 / s ▁in ▁vac u um ▁mode ▁and ▁modern ▁digital ▁machines ▁can ▁detect ▁ 5 . 1 0 − 1 0 ▁Pa · m 3 / s ▁in ▁sn iff ing ▁mode . ▁ ▁V acu um ▁test ▁ ▁Usually ▁a ▁vac u um ▁inside ▁the ▁object ▁is ▁created ▁with ▁an ▁external ▁p ump ▁connected ▁to ▁the ▁instrument . ▁Alternatively ▁hel ium ▁can ▁be