Evaluating travel distance provisions in the National Building Code of Canada: history, assumptions, current practices, and recommendations for future directions
Bibliographic record
Abstract
Commissioned under the National Research Council of Canada (NRC), this report reviews how the National Building Code of Canada (NBC) 2020 Part 3 travel distance provisions (Sentence 3.4.2.5.(1), maximum allowable distance to an exit in an emergency and related egress rules) are currently applied, what assumptions underlie them, and where clarifications would improve consistent use. The report does not evaluate enforcement or maintenance practices, expand definitions, or propose code text; priority is to clarify existing provisions and identify research needs to help inform potential future technical work by the relevant committees. Canada’s travel distance benchmarks, set in 1941–1965, remain virtually unchanged aside from minor updates. These limits were based on precedent and engineering judgment, not on empirical modelling, and reflect conditions from nearly a century ago (see Section 5). Given today’s larger, more complex buildings and diverse occupants, these prescriptive limits may no longer consistently reflect safety needs. The prescriptive travel-distance limits and related egress provisions are summarized in Section 4 of this report. It includes the objectives and functions; how distance interacts with endpoints, tenability, and vertical travel; and practical dependencies (sprinklers, smoke control/pressurization, emergency lighting, signage, wayfinding). Section 6 translates these themes into reviewable criteria, explicit tenability thresholds (see Table 3), declared system dependencies with degradation checks, visibility/wayfinding under smoke, and clear endpoints, used to demonstrate that Available Safe Egress Time (ASET) exceeds Required Safe Egress Time (RSET) to the declared endpoint. Code users noted (Section 7) that prescriptive distances work in typical buildings but fail in large or complex layouts. Participants asked for a clearer performance pathway tied to explicit tenability benchmarks, RSET inputs that reflect occupant diversity, and declared/tested dependencies. A hybrid model, prescriptive baselines with a structured performance pathway, would improve clarity, consistency, and safety across Canada.
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.069 | 0.135 |
| Meta-epidemiology (narrow) | 0.001 | 0.001 |
| Meta-epidemiology (broad) | 0.002 | 0.001 |
| Bibliometrics | 0.017 | 0.025 |
| Science and technology studies | 0.011 | 0.012 |
| Scholarly communication | 0.022 | 0.010 |
| Open science | 0.011 | 0.004 |
| Research integrity | 0.003 | 0.006 |
| Insufficient payload (model declined to judge) | 0.005 | 0.001 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one source (direct Gemma or distilled Codex), not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".