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ADAAG Manual

Note: This document, portion of document or referenced document was published prior to the 2010 ADA Standards, and all or part of this information may only apply to Safe Harbored elements.

Pulse Duration and Flash Rate

Visual alarm strobes produce a repetitive burst of high-intensity light. The repetition of this pulse at a regular interval is the flash rate. Pulse duration is the interval of the flash between signal build-up and decay and is limited as specified so that the signal is not temporarily blinding. A flash rate cycle between one to three Hz (flashes per second) is required based on research results.

Recommendation: Flash synchronization is an important consideration. Multiple strobes within a space, if not synchronized, can produce a composite flash rate in excess of 3 Hz. For example, two strobes set at 3 Hz in a room could generate a combined flash rate of 6 Hz. Flash rates above 5 Hz may trigger seizures in people with certain forms of epilepsy. This is a particular concern in schools, since children frequently are more affected by photosensitivity than are adults. In spaces with multiple strobes, composite flash rates above 5 Hz should be avoided by synchronizing or decreasing the flash rate. It may also be possible to decrease the number of strobes or increase the spacing between them by increasing their intensity.

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