Nitty gritty of compliance

One might think that the concrete T-beam and block infill arrangement would easily meet 60min REI fire resistance. The photo shows part of the ground floor of an existing four-storey office building which we are converting the ground floor to a restaurant. The client wants to leave the underside of the floor exposed and then hang the services for the restaurant from it, including the electrical installation. However, whilst the fire resistance of the floor might seem obvious, I cannot get a test report to confirm such. BC require formal confirmation. As things stand, I may have to underdraw the floor with a 60min MF and plasterboard ceiling. Now, if I do that, where does one put the services? If I put them above the ceiling, they will be above the compartment fire line and, for technical compliance, each penetration would have to be fire stopped. The correct thing to do would be to fit the MF ceiling and hang the services below it but the client only wants the services exposed if the floor slab is left exposed. So, for pedantic compliance, I will need to fit a 60 min REI MF ceiling, hang the services from the floor slab, fire stop the supports and underdraw the 60min ceiling with a decorative one such that the services are below the 60min ceiling but above the decorative one.This situation is a little bit like the RCD issue a recent post where the RCD in the My-Energi Zappi was felt unacceptable as it didn’t meet BSEN61008 so an upstream RCD was felt to be needed. The joys of nitty gritty compliance! 

  • I've never understood why people would want to eat under an exposed "industrial" ceiling. It would be impossible to keep clean, with all sorts of bits falling into your food.

    Well named thread title, nitty GRITTY.

  • Do you know whose beams and blocks they are - as in the make ?

    The makers must be in the habit of backing up the claims in their catalogues for example.

    For example Cemex claim


    What is the fire rating of the beams?

    The 155mm beam is rated as 30mins and the 225mm beam has 60mins fire rating. If required the fire rating of the overall floor can be increased for upper floors with the addition of a fire rated ceiling below the floor."

    Presumably they have test results to show that ?

    Apologies if this is stating the obvious.


  • The problem nowadays is that construction needs to be tested as a composite arrangement. Confirming that the beams are 60min does not imply that the beams and associated infill are 60min even though common sense might suggest same, more espec with a 75mm sand and cement finished floor over. This building is +25 years old pre-dating the focus on fire certification of just about everything structural. I had the same problem in an old office building that we were converting to a hotel recently. I brought a fire engineer in to advise on the fire resistance of the wooden floors. Even with computer simulation using way above average room fire load, suggesting compliance, we were unable to convince BC of the 60min REI rating without  test documentation. We did consider mocking up a section for testing but the £50K test house fee put that off! 
    Like never before, fire safety is front and centre of all projects, evident also in BS7671 and the installation of electrical services. As an aside, the qualifications attendant to electrical installation practice, such as the 2391, seem rather stuck in indirect shock protection, rarely pitching questions on fire safety.

    By the way, a rather good point Olympus Mons, yes, I have seen the dirt and grime that builds up on exposed wiring systems. I think I will book my table well away from such systems in future!

  • Morning Lyle

    I am not sure about NI but here in England your question would be one for the Fire Engineer. Us electrical bods cannot put finger to keyboard until we know what the Fire Strategy is for the building.


  • The issue here isn't the integrity of the beams (that is certified) its the integrity of the floor structure in its entirety, to the passage of smoke. The manufacturers can't guarantee there won't be tiny gaps between them when installed. I appreciate you say there is a 75mm concrete screed above, however, playing devil's advocate, how can you be sure there isn't a large crack in it, this being an older building?
    My suggestion would be to ask a specialist fire stopping company to check, seal any defects and certify it. BC would certainly accept it then. A quick google search will give you the names of suitable candidates.