By Avinash Gupta, P.Eng., Mohamed S. Mohamed, P.Eng., and Dominic Esposito, P.Eng.
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Codes leave gaps on the path to safety after terminating a building’s exits.
Whenever there is a fire emergency in a building, the most immediate response is to evacuate occupants before the environment becomes unsafe. Every area of occupancy must provide an adequate number of exits. Considerations for the effective design, protection and maintenance of these means of egress, as well as fire protection of exits, obstruction-free means of egress, exit signs and emergency lighting, are critical features.
As per the definition in Canada’s National Building Code (NBC) and National Fire Code (NFC), exits include doors or doorways leading directly to an exit stair or outside. An exit from a building does not stop at the exterior door, but must continue to provide access to (a) a public thoroughfare or (b) an exterior open space protected from fire exposure from the building and with access to a public thoroughfare. That said, the scope of NBC and NFC ceases at the termination of the means of egress.
A continuous, unobstructed path of travel from any point in a building to a public thoroughfare comprises three separate, distinct parts: access to an exit; exit; and exit discharge. It is important to address the challenges of exterior discharge and public thoroughfare.
Exterior exit discharge
The terminology of exterior discharges was introduced in the 2015 edition of NBC, but not defined. Exit discharge is a path of travel from the termination of an exit to a public thoroughfare, but the path could be inside or outside a building, such as where an exit opens onto an alley, enclosed space (court) or small, uncultivated or unpaved area (yard).
Horizontal exits are helpful in facilities like detention, treatment and care centres. In detention occupancies, where security is critical, horizontal exits provide relocation for residents, instead of allowing them to be evacuated outside. In treatment or care homes, horizontal paths help move non-ambulatory occupants from one fire compartment to an adjoining, temporary, safe fire compartment, rather than moving them downstairs.
Path of travel from exit
NBC requirements cease to apply at the termination of an exterior exit door, but as occupants will continue to move away from a burning building until they reach a safe area, further components should be implemented to make evacuation safer, such as illuminating the means of egress outside the building, emergency lighting, handrails and maintaining an obstruction-free environment of sufficient width.
Currently, NBC and NFC do not prescribe any of these components. Illumination and maintenance of public thoroughfares, alleys or unpaved or uncultivated lands or streets are not enforceable by municipal building departments, but instead are supported by wings of the provincial or federal government. Current model codes are applicable within a building, but generally not enforceable beyond the building’s perimeter.
It is important to address exterior discharge and public thoroughfare.
Exterior exit door location
A minimum distance between exterior discharges, applicable to exit doors and stairwells, was introduced in the 2015 edition of NBC to mitigate the risk of such exits being simultaneously blocked by an exterior incident (e.g. bomb threat). The provision, which does not cover all types of buildings, could be revisited.
Width and location of exterior path
NBC and NFC do not regulate the width of an exterior exit discharge or its distance from the outer surface of an exposing building face.
Designers should ensure adequate exterior walkways for high-occupancy buildings will facilitate the continuous flow of movement and prevent overcrowding and blocking of exits. Exterior unpaved walkways, grass or similar surfaces are acceptable.
Where exits discharge to an unoccupied and open yard, court or similar area, the discharge path should accommodate all occupants and provide safe access to the public thoroughfare. Based on the expected occupant load, a designer can calculate the width of the exterior path, using the concepts already provided in NBC.
Where an exit discharges to the roof of another section of the building or an adjoining building, the roof or ceiling assembly must provide fire resistance equal to or greater than that required for an exit enclosure. In addition, a continuous and safe means of egress leading to public thoroughfare must be available.
Often, the exterior exit door terminates at an open space surrounded by exterior walls, such as a parking garage. Such an enclosed court should offer adequate exits to the public thoroughfare. Once an occupant leaves a building’s protected means of egress, after all, the level of protection provided by an exit cannot be reduced.
Current model codes are applicable within a building, but generally not enforceable beyond the perimeter.
The determination of a ‘safe place,’ which is not defined by NBC or NFC, could be based on a fire radiation analysis. Use of a holding space as a safe place could also be considered based on a risk analysis of credible worst-case scenarios.
Generally, a 3-m distance from an exterior path of travel to a building is used to address fire exposure. There are discrepancies, however, in how the distance is measured (i.e. along horizontal and/or vertical planes) and situations where it is not feasible to provide a 3-m distance. In some jurisdictions, the length of the exterior path of travel to the public thoroughfare is based on NBC provisions for a single direction of egress travel within buildings.
The design of the exterior path could be based on the radiation intensity (heat flux) from a fire in the building relative to a scenario-based analysis, but current prescriptive requirements leave such interpretation to the designers and authorities having jurisdiction (AHJs), causing a massive gap. Further investigation could update NBC and NFC accordingly.
NFC requires exterior passageways and stairs to be kept free of snow and ice accumulation, but does not address the maintenance of other elements of the exterior path of travel. One of the significant issues of safe evacuation is maintaining exterior means of egress. Within the walls or perceived boundaries of a building, the owner could be held responsible for such maintenance if the local authority promulgates it in zoning bylaws.
Yet to be addressed
Thus, several elements of exterior paths of travel are not currently addressed by NBC or NFC, including design (e.g. width and surface type), exit signs, illumination and maintenance. While many safety measures are feasible within a building, exterior means of egress need co-ordination with municipal governments for their efficacious enforcement.
For now, an exterior discharge from a building is not in NBC’s territory. This leaves a massive gap between the code and what is essential for an occupant’s safe evacuation—an unconventional problem that probably needs an unconventional solution.
Avinash Gupta, P.Eng., is chief code compliance engineer and assistant fire marshal for the government of the Northwest Territories. Mohamed S. Mohamed, P.Eng., is East Canada manager for Jensen Hughes. Dominic Esposito, P.Eng., is a senior project consultant for Jensen Hughes. For more information, contact Gupta at email@example.com.
This article originally appeared in the May/June 2023 issue of Canadian Consulting Enginer.