Definition(s)
Safety Sub
Used in tubing conveyed perforating gun strings, the safety sub is the very top section that does not contain shaped charge perforators. The purpose is to place the perforator loaded guns below the rig floor when the firing head is installed to augment rig crew safety.
Source: API RP 67, Recommended Practice for Oilfield Explosives Safety, Upstream Segment, Second Edition, May 2007. Global Standards