A limited access structure is, “a structure or portion of a structure lacking emergency access openings”. To qualify as an emergency access opening the window, panel, or similar opening must meet the following criteria:
- minimum dimensions of 560mm width x 610mm high
- bottom of opening less than 1120mm AFF
- unobstructed, identifiable, and accessible from both the interior and the exterior
It is important to clearly define whether the space is considered an underground or limited access structure. Each of these have their own, and overlapping, fire protection and life safety requirements. Both structure types must meet all of the following requirements:
- Fire sprinkler system is required (with some exceptions, noted in 101:11.7.3.4)
- Sprinklers may be omitted if the following applies:
- Occupant load is 50 or fewer for new structures, 100 or less for existing
- If the structure is permitted to have a single exit (per occupancy use), and the common path of travel does not exceed 15m.
- Emergency lighting is required, throughout
In addition to these requirements, structures that expressly meet the definition of underground structure must comply with these additional requirements.
- Automatic smoke venting systems (required, if following applies):
- Occupant load is greater than 100 persons
- Occupiable floors are greater than 9.1m below exit discharge
- Space contains combustible contents, interior finishes, or construction
- Exit stair enclosures are required to have code compliant signage that points to the direction of exit discharge
This is only an encapsulation of the fire protection requirements as outlined in the Life Safety Code. There are many other factors to be considered for safe underground dwelling. Aside from the building code, loads, and material requirements, there are very real emergency response issues. These challenges include ventilation, communication, orientation, access and egress, and patient removal. In areas of occupied subterranean environments departments should be aware of their existence and have robust plans for the maintenance and enforcement of codes and standards, and emergency response.