Design Considerations for a Commonplace Peril
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 (JTG) 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 JTG’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. Does it make sense to have differing criteria for two such similar buildings?”
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. Thus 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.
Discussion about the width of exit stairs – i.e. stairwells – is a notable exception. The current code requirement and longstanding industry norm is a minimum of 1,100 millimetres (mm) or 44 inches. However, respected NFPA (National Fire Protection Association) standards now recommend at least a 56-inch (1,420 mm) 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 mm to even 1,350 mm or to 1,400 or 1,500,” Rubes says.
The CCR instigating the JTG’s contemplations suggests a minimum stair width of 1,400 mm 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 passers-by 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, very congested,” says Philip Rizcallah, Senior Technical Advisor with the Canadian Codes Centre at the National Research Council.
“If designers choose to follow the NFPA standard, that is great because the requirement was based on counter flow issues – i.e. when firefighters are attempting to go up versus the flow of occupants out of the building,” affirms Sean Tracey, the NFPA’s Canadian Regional Director. “Congestion slows down both groups, and delays evacuation and the start of firefighting operations.”
Nevertheless, such occasions should be rare if evacuations are properly coordinated. The vast majority of fires in high-rise 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.
“There is a premise that it’s not necessary to evacuate an entire sprinklered high-rise building,” Rubes says. “The twin towers are, fortunately, a very rare example of the need to completely evacuate.”
Tracey suggests many property managers simply need better training. “We want to make sure they use the two-stage alarm systems. We want to avoid a full general alarm dumping the entire building [into the stairwell] after five minutes. That’s what overloads the exits,” he stresses.
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 and/or regulators will demand in seniors’ projects.
“I have noticed that 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,” observes Michele Farley, President of Fire Consulting Services Ltd. and a member of the CCBFC’s Task Group on Use & Egress. “Certainly, wider is better when you need to evacuate in an emergency.”
Other CCRs under review focus on generally cost-neutral elements of construction in larger Part 3 buildings. “They’re more about some challenges that architects run into. It’s not really a cost implication, but it may affect design choices,” Rubes says.
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 counterclockwise direction for curved stairs to ensure that the outer curve will be on the side where users conventionally walk downward.
“In North America, like we drive on the right, we walk on the right,” Rubes explains. “It’s more important to have wider tread [i.e. the outer curve] going down than going up so, if you’re walking on the right, you’d like that wider tread to be on the right.”
The JTG 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.
“The industry group is saying that the wording itself is a fallacy because you can climb anything,” Rizcallah notes.
Design choices are now limited to smooth vertical pickets, solid glass or plexiglass panels, while critics of the current code are seeking some flexibility for more decorative railings, particularly in the residential sector.
“Again, it’s probably a bigger issue for residential buildings,” Rubes reiterates. “One of the controversies or dilemmas there is should rules that apply to safety be different in a dwelling unit than in a public building?”
CONSULTATION, COMMENT & REVIEW
The JTG 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 & Egress and Housing & Small Buildings, where they may be accepted, rejected and/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, and issues related to assembly occupancies such as theatres and stadiums. “We are looking at removing and revising all the requirements we have in the building code that deal with guards in assembly occupancies. What we have in our code now is 35 to 40 years old,” Rizcallah says.
“There will not be any amendment [to the current 2010 code] arising from any of these items,” he adds. “We are far enough into the code cycle now that if it hasn’t been considered before 2013, it will be incorporated into the next cycle for the 2015 code.”
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.
“That’s why it’s very important for people to comment,” Rubes asserts. “There is a tendency for opponents to comment and supporters to stay quiet, but when that gets communicated back to the standing committee, it sees a bunch of people objecting to it and nobody supporting it.”
For more information, see the Canadian Codes Centre’s web site at www.nationalcodes.nrc.gc.ca.