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Making the case for wood


April 24, 2014
By Len Garis and Joseph Clare

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New research comparing the outcomes of fires in residential buildings with wood, steel and concrete framing appears to bolster the case for taller wood-frame buildings.

New research comparing the outcomes of fires in residential buildings with wood, steel and concrete framing appears to bolster the case for taller wood-frame buildings.

under-construction wood-frame building  
A fire in an under-construction wood-frame building in Kingston, Ont., in December raised concerns about fire safety during construction, but a study of fire injuries and deaths in British Columbia shows that building materials are not a factor in completed structures that have sprinklers and other fire-safety measures. Photo courtesy Kingston Fire & Rescue


 

Proposed and adopted building-code changes in some provinces to permit taller wood-frame buildings, along with pending changes to the National Building Code of Canada, have sparked discussion in the fire community and among producers of building materials about the safety of wood-frame buildings.

The report – Fire Outcomes in Residential Fires by General Construction Type – which was released in February by the University of the Fraser Valley in British Columbia, challenges the perception that completed buildings constructed predominantly with steel or concrete are safer in fires than those built predominantly with wood.

While a Dec. 17 fire in a half-finished wood-frame building in Kingston, Ont., drew attention to the greater fire risk and lack of fire safety regulations related to buildings under construction, the report data indicates that completed buildings do not share this risk. 

“ . . . there appears to be little difference with respect to fire spread, death and injury rates as a function of building general construction type, provided these buildings have functioning smoke alarms and complete sprinkler protection,” the report says.

“With these findings in mind, and in parallel with other research findings from the authors, it should be considered that more emphasis is placed on ensuring all buildings have operating, current and optimal fire safety systems.”

The report reviewed 11,875 fires in residential buildings that could be grouped within five broad general construction types. These fires were a subset of a total of 34,708 fires reported to the BC Office of the Fire Commissioner between October 2008 and October 2013. The 11,875 fires, which caused 772 injuries and 107 deaths, were divided into five construction-type categories for comparison purposes. Described simply, they are:

  • Unprotected wood construction – exposed wood joists and
  • trusses (in buildings under construction)
  • Protected wood construction – wood joists and trusses protected by plaster or gyproc (after construction is completed)
  • Heavy timber construction
  • Unprotected steel construction – exposed steel joists and trusses (in buildings under construction)
  • Protected steel or concrete construction (after construction is completed)

Overall, the report shows that the fire safety of buildings has more to do with effective fire-safety systems, such as working smoke alarms and sprinkler protection, than with the construction materials.

When effective fire safety systems were not factored into the analysis, this dataset showed that fires were more often contained to the point of origin in steel and concrete buildings than in wood-frame buildings. However, in buildings with complete sprinkler systems, there was little difference in the spread of fire among the different building types.

The same was true when injuries and deaths were considered: in these particular fires, steel and concrete buildings had lower death and injury rates per fire when effective fire-safety systems were not factored in, but buildings of all construction types had similar death and injury rates when these systems were present. In fact, when working smoke alarms and complete sprinkler systems were in place, there were no reported fatalities from the fires – regardless of the type of building construction.

When looking at this particular set of 11,875 fires – including both sprinklered and non-sprinklered buildings – the data shows:

  • 66 per cent of the fires, 75 per cent of injuries (7.4 injuries per 100 fires) and 62 per cent of deaths (.85 deaths per 100 fires) occurred in buildings with protected wood construction.
  • 19 per cent of fires, 14 per cent of injuries (5.0 injuries per 100 fires) and 30 per cent of deaths (1.4 deaths per 100 fires) occurred in buildings with unprotected wood construction.
  • Nine per cent of fires, six per cent of injuries (4.5 injuries per 100 fires) and six per cent of deaths (.57 deaths per 100 fires) occurred in protected steel or concrete construction.
  • Four per cent of fires, three per cent of injuries (4.3 injuries per 100 fires) and one per cent of deaths (.20 deaths per 100 fires) occurred in unprotected steel construction.
  • Two per cent of fires, one per cent of injuries (4.4 injuries per 100 fires) and two per cent of deaths (.88 deaths per 100 fires) occurred in heavy timber construction.

When the effect of sprinkler protection was ignored, fires were confined to at least the room of origin 92 per cent of the time in protected steel or concrete construction, 76 per cent of the time in unprotected steel construction, 71 per cent of the time in protected wood construction, 51 per cent of the time in unprotected wood construction and 47 per cent of the time in heavy timber construction.

However, when sprinkler and smoke-alarm protection was factored in, the spread of fire (i.e., fire confined to the room of origin) was similar across building types: 94 per cent in protected steel or concrete construction, 84 per cent in unprotected steel construction, 88 per cent in protected wood construction, 91 per cent in unprotected wood construction and 80 per cent in heavy timber construction.

When the effect of sprinkler protection was ignored, the data for this group of fires showed that most of the fires, and therefore most of the deaths and injuries, occurred in buildings with wood construction. Buildings with protected wood construction accounted for 75 per cent of injuries and 62 per cent of deaths, unprotected wood construction accounted for 14 per cent of injuries and 30 per cent of deaths, protected steel and concrete construction for six per cent of injuries and six per cent of deaths, unprotected steel construction for three per cent of injuries and one per cent of deaths, and heavy timber for one per cent of injuries and two per cent of deaths.

The picture changes when the effect of working smoke alarms and complete sprinkler systems is considered. The presence of a working smoke alarm reduces the death rate for all construction types, while the presence of a sprinkler system brings the death rate to zero for all types.

The data also shows a reduction in the rate of injuries across the board for all construction types with sprinkler systems, but an increase – except for heavy timber construction – when smoke alarms are the only fire-protection system. This is consistent with previous research, likely because occupants alerted to a fire by their alarms are more likely to be injured while trying to extinguish the fires themselves.

The use of both smoke alarms and sprinklers further levels – or even narrows – the playing field.

The renewed interest in the use of wood as a building material – and the debate about fire safety – is not unique to Canada. South of the border, the NFPA released a report in December through its Fire Protection Research Foundation titled Fire Safety Challenges of Tall Wood Buildings (go to nfpa.org and search the title). Representing the first phase of a planned multi-phase study, the report looks at existing research and identifies gaps that would further the understanding of fire performance of tall wood buildings (those six storeys or higher). The authors cite a number of international case studies of tall wood buildings that have been constructed and research showing the effectiveness of automatic sprinklers in controlling fires and limiting fire damage in wood buildings.

As the debate continues over the fire safety of wood buildings, both the UFV and NFPA reports offer insight and scientific data to decision makers seeking to update and improve building practices in Canada.

To read the full report, go to the reports and publications section at www.ufv.ca/cjsr .


Len Garis is the fire chief for the City of Surrey, B.C. Contact him at LWGaris@surrey.ca.
Dr. Joseph Clare is an adjunct professor at the University of Western Australia and faculty member of the Institute of Canadian Urban Research Studies. Contact him at joe.clare@uwa.edu.au.


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