2019 CSCE Annual Conference - Laval (Greater Montreal)

2019 CSCE Annual Conference - Laval (Greater Montreal) Conference

Evacuation Modelling Procedures for Improving Timber Fire Design

Ms. Bronwyn Chorlton, York University (Presenter)
Dr. John Gales, York University

Timber structures are undergoing a renaissance in Canada. Architects desire that the structures be left exposed, without encapsulation so as to exploit our natural psychological biophilia tendencies. This demand of leaving the timber members exposed and unencapsulated brings substantial challenges for the engineer to ensure fire safe design. International practice for unencapsulated timber structures has subsequently moved to consider an increase in the prescriptive fire rating required for this type of building to compensate for the calculated increase in subsequent fire load (a transient fuel load calculated on the basis of charring rates). This procedure, with limitation, negates the effects of ventilation and oxygen supply which will influence the timber’s actual contribution to the fire. Fire Dynamics aside for now, further the argument is made that the required fire rating is increased on the premise of allowing for safe evacuation owing to the additional fire load present. Herein, the authors consider the basis of evacuation modelling that can be tailored specific to the occupancy type as well as a quantifiable study of the fire risk of exposed timber. When these are considered, evacuation times can actually be lowered and therefore when assessed in parallel to the timber’s increased fuel load, the increased fuel load is not a hindrance with respect to egress situations to ensure safety. An accurate demonstration of an alternative design solution then becomes achievable. Within the proposed manuscript, the authors provide a hypothetical tall timber structural and architectural Canadian design which takes into account the increased needs for accessibility of its occupants for emergency egress. This evacuation analysis, which is based upon realistic protective action decision making methodologies developed by the authors to speed pre evacuation, demonstrates that egress speeds faster than the prescriptive requirement are observed when accessibility needs are thoroughly addressed, increasing safety without compromising the exposed timber spaces. The paper will provide a comparison between typical European and Canadian design guidance for tall timber fire safety (evacuation and coupled fire dynamics in a timber structure), as well as establish a framework of research in order to promote design solutions for tall timber construction in Canada.