Building Design and Construction Handbook - Merritt - Ventech!

16.2 SECTION SIXTEEN
Class I systems may be divided into two subclasses, A and B. Class IA systems
can be used by people both under normal and emergency conditions as a means of
egress. This class includes ramps, stairs, and escalators (powered stairs) that meet
requirements for means of egress specified in building codes or the National Fire
Protection Association ‘‘Life Safety Code’’ (see Art. 3.5.10). Systems not acceptable
as an emergency means of egress comprise Class IB. (Such systems nevertheless
may be used for emergency evacuation of a building, but the capacity of Class IA
systems alone must be sufficient for rapid, safe evacuation of the maximum probable
building population.)
16.2 RAMPS
When space permits, a sloping surface, or ramp, can be used to connect different
levels or floors (Fig. 16.1). As a means of saving space in some garages, every
floor serves as a ramp. Each floor is split longitudinally, each section sloping gradually
in opposite directions to meet the next level above and below.
Ramps are especially useful when large numbers of people or vehicles have to
be moved from floor to floor. So they are frequently adopted for public buildings,
such as railroad stations, stadiums, and exhibition halls. And they are either legally
required or highly desirable for all buildings, especially to accommodate persons
in wheelchairs. In all cases, ramps should be constructed with a nonslip surface.
Ramps have been built with slopes up to 15% (15 ft in 100 ft), but 8% is a
preferred maximum. Some idea of the space required for a ramp may be obtained
from the following: With the 8% maximum slope and a story height of, say, 8 ft,
a ramp connecting two floors is 100 ft long (Fig. 16.1a). The ramp need not be
straight for the whole distance, however. It can be curved, zigzagged (Fig. 16.1b),
or spiraled. Level landings, with a length of at least 44 in in the direction of travel,
should be provided at door openings and where ramps change slope or direction
abruptly. Ramps and landings should be designed for a live load of at least 100 lb/
FIGURE 16.1 Types of ramps: (a) straight ramp; (b) zigzag ramp.