Foam board in cold air return?

[Bryan]

This is a cold air return with foam insulation board used to block electrical wires in the stud cavity of a 3 year old home. Logic tells me this is not correct and the only code reference I can find is: M1601.2.1 Duct insulation materials.

Duct insulation materials shall conform to the following requirements:

1. Duct coverings and linings shall have a flame-spread index not greater than 25, and a smoke-developed index not greater than 50 when tested in accordance with ASTM E 84. Specimens tested in accordance with ASTM E 84 shall be representative of the final composite material.

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Does this apply or is there a better code reference?

Bryan

[genduct]

A joist or stud space (with wooden studs) can be used as return duct and you think this standard building material is worse? If that is true it certainly sounds like an inconsistency.

[Marc]

I think that foam board is approved for use as sheathing but not as duct liner. Perhaps the markings on it will tell whether it has passed that standard (ASTM E 84) or not.

Marc