upgrade existing concrete hollow beam floor to 4 hours fire resistance

[kurnal]

I have been looking at a redevelopment of an existing building in which the developer wishes to install an oil filled substation in part of the ground floor  underneath what will be a hotel. The existing hollow beam concrete floor with screed is rated at 1 hour, elements of structure under ADB  may require 60 or  90 minutes depending on interpretation.

But the client wishs to follow LPC design guide and enclose the substation in 4 hours FR. Clearly the walls are easy- blockwork- but I am struggling to come up with a solution for upgrading the underside of the existing floor without thick additional concrete.

I am uneasy with the architects  ad hoc solution of adding a  two hour and one hour board based solution from the white book because the composite will not have been tested.

Is anybody aware of any method by which this may be done please?

(Since placing the original post I have found a possible durasteel solution but would still be grateful to hear  any other views).

[Fishy]

Ceramic fibre board might do it - Isofrax is one type.  Meant for the offshore industry (e.g. H120 - withstands 1100 degrees C for nearly two hours).  IMHO H120 would give equivalent 'real' protection compared to 240 mins to BS 476 (or whatever it's called these days).

More or less nobody tests their products to four hours anymore, since it got dumped from the E&W ADB.

[Peter R]

You might look at steel faced, mineral wool core composite panels. Could be easier to handle and certainly less weight. Thickness in range 150mm to 200mm. Manufacturers have tested these to 4 hours insulation and integrity using BS476 Part 22. You would need advice on fixings which would be critical. Call Eurobond in UK or Paroc from Finland.

[wee brian]

You can tie youself up in knots with this kind of thing. You are, of course, right that sticking a series of different boards to a floor wont necessarily give a cumulative period of fire resistance.

You could get a fire resistance assessment from a suitably qualified person (most of the test houses offer this service). Or you could just accept that sticking lots of insulation on the floor will probably be better than nothing.