▁different ▁discipl ines . ▁ ▁This ▁is ▁a ▁time ▁based ▁model ▁that ▁describes ▁the ▁probability ▁of ▁a ▁system ▁operator ’ s ▁failure ▁as ▁a ▁multip lic ative ▁function ▁of ▁ 5 ▁main ▁factors . ▁These ▁factors ▁are ▁as ▁follows : ▁▁ ▁K 1 : ▁The ▁type ▁of ▁task ▁to ▁be ▁executed ▁ ▁K 2 : ▁The ▁time ▁available ▁to ▁the ▁operator ▁to ▁complete ▁the ▁task ▁ ▁K 3 : ▁The ▁operator ’ s ▁level ▁of ▁experience / character istics ▁ ▁K 4 : ▁The ▁operator ’ s ▁state ▁of ▁mind ▁ ▁K 5 : ▁The ▁environmental ▁and ▁erg onom ic ▁conditions ▁pre val ent ▁ ▁Using ▁these ▁figures , ▁an ▁overall ▁Human ▁Error ▁Pro b ability ▁( HE P ) ▁can ▁be ▁calculated ▁with ▁the ▁form ulation ▁provided ▁below : ▁ ▁K 1 ▁x ▁K 2 ▁x ▁K 3 ▁x ▁K 4 ▁x ▁K 5 ▁ ▁The ▁specific ▁value ▁of ▁each ▁of ▁the ▁above ▁functions ▁can ▁be ▁obtained ▁by ▁consult ing ▁standard ▁tables ▁that ▁take ▁account ▁of ▁the ▁method ▁in ▁which ▁the ▁H EP ▁is ▁derived . ▁ ▁Background ▁Develop ed ▁in ▁ 1 9 8 0 ▁by ▁B ello ▁and ▁Colomb ari , ▁TE SE O ▁created ▁with ▁the ▁intention ▁of ▁using ▁it ▁for ▁the ▁purpose ▁of ▁conduct ing ▁H RA ▁of ▁process ▁indust ries . ▁The ▁method ology ▁is ▁relatively ▁straightforward ▁and ▁is ▁easy ▁to ▁use ▁but ▁is ▁also ▁limited ; ▁it ▁is ▁useful ▁for ▁quick ▁over view ▁H RA ▁assess ments , ▁as ▁opposed ▁to ▁highly ▁detailed ▁and ▁in -