Table 5.1 – Limited Access Spaces and Machinery Spaces
Current Guidelines:  4.1.1  Application.  . . .

(5)  General Exceptions. . . .
 
(b)  Accessibility is not required to or in: . . .

(ii)  non-occupiable spaces accessed only by ladders, catwalks, crawl spaces, very narrow passageways, tunnels, or freight (non-passenger) elevators, and frequented only by service personnel for maintenance, repair, or occasional monitoring of equipment; such spaces may include, but are not limited to, elevator pits, elevator penthouses, piping or equipment catwalks, water or sewage treatment pump rooms and stations, electric substations and transformer vaults, and highway and tunnel facilities; . . .
Final Revised Guidelines:  203.4 Limited Access Spaces.  Spaces accessed only by ladders, catwalks, crawl spaces, or very narrow passageways shall not be required to comply with these requirements or to be on an accessible route.

203.5  Machinery Spaces.  Spaces frequented only by service personnel for maintenance, repair, or occasional monitoring of equipment shall not be required to comply with these requirements or to be on an accessible route.  Machinery spaces include, but are not limited to, elevator pits or elevator pent-houses; mechanical, electrical, or communications equipment rooms; piping or equipment catwalks; water or sewage treatment pump rooms and stations; electrical substations and transformer vaults; and highway and traffic tunnel facilities.
Model Codes & Standards
IBC 2000:  Sections 1103.2.8 and 1103.2.9 have similar exceptions for limited access spaces and machinery spaces.

IBC 2003:  Sections 1103.2.8 and 1103.2.9 have similar exceptions for limited access spaces and machinery spaces.