stairwell

Caution afoot

Design considerations for a commonplace peril
Tuesday, October 30, 2012
By Barbara Carss

As an open passage to a vertical drop, stairs are one of the most prominent hazards in a building, yet also the route to safety in an emergency evacuation. Configuration, handrails, step dimensions and surface tread all play a role in how sure-footedly users can descend or ascend.

Space between risers or guardrails poses additional risk for tripping, catching or tempting transgressors to drop items through the gaps. Meanwhile, an aging population and the trend to a larger body mass index are challenging traditional assumptions about the clearance required for upward and downward traffic to pass side by side.

Engineering and life safety specialists advising the Canadian Commission on Building and Fire Codes (CCBFC) are currently examining all of these concerns in preparation for possible new or revised rules that would be introduced in the next edition of the National Building Code in 2015. The joint task group on stairs, ramps, handrails and guards has tackled an accumulation of submissions requesting changes to the building code – commonly known by the acronym CCRs for code change requests – related to both larger buildings covered in Part 3 of the code and small buildings covered in Part 9.

“We were mandated to look at a lot of outstanding CCRs, some from nearly 20 years ago, and also to look at the inconsistencies between Part 3 and Part 9,” says Jonathan Rubes, the joint task group’s co-chair and principal of the engineering firm, Rubes Code Consultants. “For example, a 600-square-metre, three-storey public building falls under Part 9, while a 700-square-metre building is governed by Part 3.”

Harmonization of those criteria would be less pertinent for developers or designers of larger commercial, institutional and multi-residential buildings since Part 3 requirements already represent the more stringent level of safety in almost every case. So far, most of the potentially contentious measures under consideration would affect stairs in residential dwellings. Impacts in larger buildings would more likely take the form of new restrictions on design choices rather than increased capital costs.

Evacuation logistics
Discussion about the width of exit stairs (stairwells) is a notable exception. The current code requirement and long-standing industry norm is a minimum of 1,100 millimetres or 44 inches. However, respected NFPA (National Fire Protection Association) standards now recommend at least a 56-inch (1,420 millimitre) stair width in buildings where the stairs would potentially carry an occupancy load of 2,000 or more people.

“There are cost implications if you increase a stair from 1,100 millimetres to 1,350 millimetres, 1,400 millimetres or (even) 1,500 millimetres,” says Rubes.

The CCR instigating the joint task group’s contemplations suggests a minimum stair width of 1,400 millimetres in Part 3 buildings to respond to the increase in body mass index across the overall population. Narrower widths can also be more problematic if parallel lines of passersby cross into and obstruct each other’s path.

“If there are a large number of people coming down the stairs and you’ve got the fire department coming up, it can become very congested,” says Philip Rizcallah, a senior technical advisor with the Canadian Codes Centre at the National Research Council.

“Congestion slows down both groups, and delays evacuation and the start of firefighting operations,” says Sean Tracey, the NFPA’s Canadian regional director.

Nevertheless, such occasions should be rare if evacuations are properly coordinated. The vast majority of fires in highrise buildings are contained to one floor and two-stage fire alarms provide a tool for orderly phased evacuations. Knowledgeable observers aren’t predicting any imminent move to change the code, in large part because, with one indelible exception, there are few precedents for the concern.

Tracey suggests many building managers simply need better training.

“We want to make sure they use the two-stage alarm systems,” he says. “We want to avoid a full general alarm dumping the entire building (into the stairwell) after five minutes. That’s what overloads the exits.”

Even if wider stairwells weren’t universally required, the building code can and does mandate enhanced safety measures for certain types of occupancies, while developers can always voluntarily opt to build wider stairwells. That’s likely antithetical to the current condominium market economics, in which neither developers nor prospective buyers would choose to forego dwelling unit space to the stairwell, but it could be a feature the market or regulators will demand in seniors’ projects.

“I have noticed there are considerably wider stairwells in some of the newer retirement lifestyle buildings and that would obviously be a benefit if emergency services needs to bring someone down the stairwell in a gurney chair,” says Michele Farley, president of Fire Consulting Services Ltd. and a member of the CCBFC’s task group on use and egress.

Low capital safeguards
Other CCRs under review focus on generally cost-neutral elements of construction in larger Part 3 buildings.

These include consideration of handrail shape, current inconsistent handrail height requirements between the stairs and the landing, the configuration of mixed run stairs that include both straight and curved sections, and whether the code should specify a counter-clockwise direction for curved stairs to ensure the outer curve is on the side where users conventionally walk downward.

The joint task group is also taking a second look at the protective barrier guarding the open edge of the stairs – commonly known as the guard – following a failed attempt to introduce a code amendment in this current code cycle. Proponents for the Canadian railing manufacturing industry have called for a relaxation of the current prohibition on climbable guards.

Design choices are now limited to smooth vertical pickets, solid glass or Plexiglas panels, while critics of the current code are seeking some flexibility for more decorative railings, particularly in the residential sector.

Consultation, comment and review
The joint task group is managing its work through four sub-task groups to specifically address fall protection, structural loads, width and height, and dimension and configuration. Final recommendations will be forwarded to two CCBFC standing committees – for use and egress, and housing and small buildings – where they may be accepted, rejected or revised, or the standing committees may add recommendations of their own.

Other separate task groups are also studying accessibility in relation to stairs, ramps and handrails as well as issues related to assembly occupancies such as theatres and stadiums.

All changes recommended for the 2015 code will be released for public review and comment. Applicable standing committees will then review the responses before issuing final recommendations.

Barbara Carss is editor-in-chief of Canadian Property Management magazine.

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