Smoke Obscuration Calculator

Calculate smoke obscuration levels and visibility distance for fire alarm design and egress analysis.

Input Parameters

Results

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Obscuration
%/ft
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Obscuration
%/m
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Visibility Distance
ft
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Detector Activation
Note: Smoke detector sensitivity per NFPA 72 ranges from 0.5 to 4.0 %/ft obscuration. UL 268 lists detector sensitivity. For egress, visibility below 10m (33ft) impairs wayfinding. Mass optical density helps correlate to detector response.

Reference

Obscuration (%/m) = (1 - 10^(-OD)) x 100 Obscuration (%/ft) = (1 - 10^(-OD x 0.3048)) x 100 Visibility = 3 / (2.303 x OD) meters (reflective signs) Bouguer-Lambert Law: I/I0 = 10^(-OD x L) NFPA 72 smoke detectors: 0.5-4.0 %/ft obscuration range