Determining Fire Resistance of Cement Asbestos

[Messy]

I have been asked to post this question and would be grateful if anyone could help

The scenario:

Residential multiple floor building, penetrated between floors by a ventilation system, consisting of asbestos cement ducting.
Investigations have determined that the ducting is 7mm thick.

How can I determine (or reliably estimate) the fire resistance in terms of minutes of this material?

I've heard plenty of anecdotal descriptions of asbestos pipework being the only thing left after serious fires, but ultimately that sort of thing isn't much help in making any definitive statements...

For reference, my best source so far has been this: http://www.fireriskheritage.net/wp-cont ... atings.pdf However the suggestion of just 10 minutes' resistence for ~5mm, and 45 minutes for ~19mm seems far too low for common sense.

[AnthonyB]

The (recently archived) BR128 "Guidelines for the construction of fire-resisting structural elements" does reference asbestos and says that to get 30 minutes fire resistance you need 9 - 12mm of asbestos boarding dependant on the type of partition and method of fixing.

It's fire resistance data for concrete doesn't give asbestos cement a separate listing and uses the type of concrete application and whether its dense or lightweight to form it's tables, but might give you some idea 

[Fishy]

Don't forget - when referring to 'fire resistance' in most cases it's integrity and insulation that guidance recommends (a common exception being doorsets).  Whilst a relatively thin sheet of asbestos might sit there maintaining integrity for > 10 mins, it's highly likely that it would fail insulation around that time.

[Goodsparks]

https://shop.bsigroup.com/ProductDetail/?pid=000000000000097167

This document is probably worth a shot, the markings on the jointing sleeves should confirm whether it?s the light or heavy duty version that?s installed.