Which type of oil is deemed safest for quenching oil-hardening parts?

High flashpoint quenching oil is considered the safest option for quenching oil-hardening parts due to its ability to maintain a stable ignition temperature. Quenching involves rapidly cooling a hot metal part, which can create significant heat and flammable vapors. The high flashpoint characteristic means that this type of oil will not ignite easily during the quenching process, reducing the risk of fire and explosions in the workshop environment.

Moreover, high flashpoint quenching oils are specifically formulated to provide effective cooling and prevent thermal shock while minimizing potential hazards associated with lower flashpoint oils. This specialized formulation helps ensure that the quenching process does not compromise the integrity of the metal, while also prioritizing safety for the operator and the surrounding area during heat treatment operations.

The other types of oil mentioned may not provide the same level of safety as high flashpoint quenching oils, especially in the context of handling hot metal parts that can generate flammable vapors.