The following points need to be taken into account.

Taken from:

Building Regulations 2000 Manual Approved Document B:
 Fire Safety - page 66  (download whole pdf (10MB))

LOADBEARING ELEMENTS OF STRUCTURE

Raised Storage Areas (Page 66)

8.8   Raised free standing floors (sometimes supported by racking) are frequently erected in single-storey industrial buildings. Whether the structure is considered as a gallery, or is of sufficient size that it is considered as a floor forming an additional storey, the normal provisions for fire resistance of elements of structure may be onerous if applied to the raised storage area.

8.9   A structure which does not have the appropriate fire resistance given in Appendix A, Table A1 is acceptable provided the following conditions are satisfied:

• the structure has only one tier and is used for storage purposes only;
• the number of persons likely to be on the floor at any one time is low and does not include members of the public;
• the floor is not more than 10.0 in either width or length and does not exceed one half of the floor area of the space in which it is situated;
• the floor is open above and below to the room or space in which it is situated; and
• the means of escape from the floor meets the relevant provisions in Section 4, 5 and 6.

Notes:

1. Where the lower level is provided with an automatic detection and alarm system meeting the relevant recommendations of BS 5839: Part 1 Fire detection and alarm systems for buildings. Code of practice for system design, installation and servicing, then the floor size may be increased to no more than 20m in either width or length.

2. Where the building is fitted throughout with an automatic sprinkler system meeting the relevant recommendations of BS 5306-2 Fire extinguishing installations and equipment on premises. Specification for sprinkler systems, i.e. the relevant occupancy rating together with the additional requirements for life safety, there is no limits on the size of the floor.

See also:

Building Regulations 2000 Manual Approved Document K:
 Protection form falling, collision & impact  (download pdf (1.5MB))

Building Regulations 2000 Manual Approved Document M:
 Access to and use of buildings  (download pdf (2.2MB))