Glossary of Firefighting - O

O

• Occupancy: Zoning and safety code term used to determine how a structure is permitted to be used and occupied, which in turn dictates the necessary safety structures and procedures.
• Occupancy class: General categories of structures for purpose of safety planning, such as for hospital, assembly, industrial, single-family dwelling, apartment building, commercial, etc. Further broken down by types of hazards associated with particular occupancies, such as gas stations.
• Occupant use hose: Light-weight 1½" diameter firehose pre-coupled to standpipe for emergency use by building occupants prior to arrival of firefighters. Often accessible by breaking glass to unlock a secure enclosure.
• Offensive attack: Method of firefighting in which water or other extinguishing agent is taken by firefighters, directly to the seat of the fire, as opposed to being pumped in that general direction from a safe distance. Typified by taking hoselines to the interior of a building as opposed to remaining on the outside, aka "surround and drown."
• On-call: Personnel who can be summoned (and paid) when necessary to respond to an incident; a type of "volunteer" fire department.
• OSHA: U.S. government agency concerned with regulating employee safety, particularly in hazardous occupations such as firefighting.
• Outside fire: Urban fire not inside a building or vehicle, often found to be burning trash which could extend to nearby structures or vehicles if not dealt with properly. A suburban, interface, or rural outside fire could also be a wildland fire.
• Overhauling: Late stage in fire-suppression process during which the burned area is carefully examined for remaining sources of heat that may re-kindle the fire. Often coincides with salvage operations to prevent further loss to structure or its contents, as well as fire-cause determination and preservation of evidence.
• Oxidizer: A hazardous material containing oxygen that can combine with adjacent fuel to start or feed a fire.