Chapter 4 - Spatial considerations

Abstract

The chapter focuses on indoor and outdoor locations, roofed spaces in hazardous areas, nonhazardous spaces above or below hazardous areas, spaces giving access to hazardous areas. In indoor locations, air movements may not be as favorable as in outdoor locations. This is because of the obstructions natural ventilation may encounter. Access openings have no impact on whether the location should be considered as indoors or outdoors. Roofed spaces without a source of hazard normally do not require classification, unless they are located in a hazardous area. Even if they are located in a hazardous area, they can be classified as non-hazardous provided there is sufficient ventilation, and a suitable safeguard. Roofed spaces that have only one or no walls are normally considered sufficiently ventilated by natural ventilation. However, roofed spaces still need safeguards in spite of non hazardous location because ignitable gases or vapors may enter the non hazardous space. The chapter illustrates a tabular representation of roofed spaces in hazardous locations and non hazardous spaces above or below hazardous areas, Natural ventilation is capable of diluting and dispersing any flammable material in roofed spaces, because of the lack of air pockets. A location is considered outdoors when natural ventilation is restricted to not more than 25% of the building enclosure in passing through the location. This means that the location has no corners in which a flammable gas or vapor can accumulate. Usually Under three different conditions a flammable gas or vapor is released from a source of hazard: (1) a continuous release from the open sources of hazard. (2) A frequent release from closed sources of hazard; as a result of frequent repairs and maintenance. (3) An occasional release from the closed sources of hazard; as a result of a failure of the sources of hazard.