Concealed spaces

Fire risk assessment is made in order to determine the overall value of decreasing fire hazard in a particular scenario. The level of fire risk that is acceptable for a situation is, normally, a societal, and not a technical, decision. Therefore, fire hazard assessments are generally more common than fire risk assessments. The NFPA Research Foundation has undertaken a project to develop a methodology for fire risk assessment. It has done this by studying four cases in detail upholstered furniture in residential environments, wire and cable in concealed spaces in hotels and motels, floor coverings in offices and wall coverings in restaurants. 

In office buildings it is very common to have plenums, i.e. spaces above rooms where the air handling system is located, together with electrical wires and cables, as well as abundant wood and other construction materials. These concealed spaces are usually ca. 1 m (3 ft) high and are invisible from the room below. 

In the 1980 s years there has been some controversy about the effect of fires involving combustible products contained in such concealed spaces. This addresses the room-plenum scenario both when a fire starts in the room and when a fire starts in the plenum and investigates its spread into the room below. 

As discussed earlier, NFPA 13011 is another important document, because it is used for the regulation of train and underground system, by authorities having jurisdiction over local rail systems in some U.S. systems, some Canadian ones, and some Asian ones. Table 21.6 shows the reaction-to-fire requirements for rail cars. NFPA 130 also includes requirements for stations and trainways as well as rail vehicles. The key issues to be considered in stations are the same as in other assembly occupancies, namely electrical, interior finish, upholstered furniture, decorations, and trash disposal. With regard to trainways, the standard looks at the effect of areas that are potentially concealed spaces and considers that factor. 

Wall or floor openings within a 35-foot (10.7-m) radius expose combustible materials in adjacent areas, including concealed spaces in walls or floors. 

Cavity barrier is the arrangement provided in a cavity, such as a loft space, or a concealed space to prevent the penetration or movement of smoke or flame within such a space. 

Automatic sprinkler protection shall be designed and installed in the plenum and interstitial space above cleanrooms in accordance with NFPA 13, (NFPA 318 2-1.2.5). NFPA 13 does have some exceptions for concealed spaces, however. 

The building shall be designed and constructed so that the unseen spread of fire and smoke within concealed spaces in its structure and fabric is inhibited. 

Concealed spaces in buildings provide easy routes for fire to escape both horizontally and vertically. Fire... 

Concealed spaces are found in numerous locations in a building including ... 

Roofs. Roofs shall be without concealed spaces and wood roof decks shall be sawn or glued laminated, splined or tongue-and-groove plank, not less than 2 inches (51 nun) nominal in thickness,... 

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