I agree with Chris. Have you considered having all your lap tops and PC's linked to a main server and having this server located in a fire and heat proof enclosure? There are companies that make these and they protect your server as well as the data. The idea being that if there is need to evacuate the building, all data is streamed down to the server. Try
http://www.securesafe.co.uk they stock Lampertz server safes but there are others such as Rosengrens.
As I recall, these units come complete with air conditioning and there own fire extinguishing and smoke detection system. I believe they cost more than a few hundred pounds..... but you have to way this up along with the risk associated with having your staff hang around to remove lap tops.
Can you advise us whether your fire alarm system in manual only or does it have full smoke detection? This should influence your decision about delays in evacuation. If there is no smoke detection and the alarm is activated once someone 'finds' a fire, then time is of the essence and your staff should leave immediately. Also, is your admin. building attached to a warehouse or factory and if it is what is being stored or made? This would have an effect as well on fire size and smoke propagation, etc.
Another solution is to look at your fire alarm system. You give no indication as to the size of your building, but would your fire alarm system enable you to give a staged evacuation. What this does is operate the sounders in the fire effected zone on a constant tone indicating to anyone within that area to 'get out now.' In other areas the sounders operate on an intermittent basis indicating to staff in these areas to 'standby to get out.' At this time your staff could unplug, pack up and make ready to leave the building. There is more to this type of system than this but in essence that's the concept.
It's all down to the age old equation 'life verses cost verses business interruption'