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The aim of this document is to provide designers with correlations that can be used in performance-based fire safety design to represent the reduction of movement speed of building occupants when walking in an environment with low visibility, which also contains irritants. Different correlations are provided for deterministic analysis and probabilistic analysis.

It is recognized that values for visibility and irritant species concentration can be used as performance criteria in performance-based fire safety design. Performance criteria related to visibility and irritant species are not specified in this document. However, it is always necessary to take into account relevant performance criteria when applying this document. For example, an occupant cannot be assumed to continue moving if a performance criterion related to visibility or irritant species concentration is violated in the design calculations.

It is also recognized that fire smoke can have an influence on the cognitive processes of occupants during evacuation. This type of influence on cognition is not covered in this document but can be considered if deemed to have a major impact.

Fire smoke can also influence behaviour (e.g. occupants changing their movement path if moving into worsening smoke conditions). This type of behaviour change is not included in this document but can be considered if deemed to have a major impact.

In some jurisdictions, it is not permitted to include fire smoke in escape routes as part of the fire safety design; this document is not applicable in such situations.