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Cables and reaction to fire

lyledunn
Why do you suppose that the MHCLG did not feel it necessary to mandate levels of performance for cables with respect to their reaction to fire as was their prerogative under CPR?

Clearly the current non-prescriptive approach is either working or there is no significant evidence that cables and wiring systems have unduly contributed to the propagation of a fire or resulted in emissions that made a situation untenable when it would not have otherwise been. 

Further, what does it actually mean in the note in 422.2.1 that cables need to satisfy the requirements of the CPR in terms of their reaction to fire? I can find nothing specific in the CPR other than the need for CE marking and the requirements placed on the manufacturers for technical information.
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    Why do you suppose that the MHCLG did not feel it necessary to mandate levels of performance for cables with respect to their reaction to fire as was their prerogative under CPR?



    Maybe they're just been too busy with UK-EU exit preparations?


    Or maybe they think that the general requirements (EN 50575) plus the requirements of specific standards (BS 7671, BS 6701, BS 5839 etc) already deal with the matter sufficiently.


      I'm just guessing.


        - Andy.
  • Former Community Member
    0 Former Community Member
    The CPR calls up various classes of cable reaction to fire. BS 7671 places the responsibility on the designer to select the correct classification based on risk assessment (for power cables) and compliance with other standards for "IT" cabling.


    As you can probably guess, most designers are now specifying a pretty high classification for cables (rather than do the Risk Assessment)


    In various parts of the EU, national codes mandate a particular class based on the premises type (so Healthcare would be Cca, as an example)


    Regards


    OMS


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    Not sure what you mean by 7671 requiring risk assessment OMS, but I do understand the imperatives for designers selecting cables with better performance in fire. However, imperatives should be evidence-based and I can find nothing in the way of forensic reports detailing the contribution cabling made in real fire situations. For example, it would seem reasonable that cables with improved fire performance are installed say in a hotel situation but, equally, not unreasonable that they are not. Some designers, on the other hand, will  opt for the former under the pressure of perceived imperatives. In other words, if the designer specifies LSF cable for the bedrooms, for example, they might assume that risk has been reduced from what it otherwise would have been had standard twin and earth cables been used. Since bunching would be unlikely in the voids above bedrooms, fire safety may not have been improved one jot but it just seems that by specifying LSF the right thing has been done irrespective of cost to the client. 

    Dont get me wrong, I am an advocate of  meticulous consideration of fire safety measures for buildings but I just get the impression that we are responding in an almost knee-jerk fashion due to rightful focus on recent tragic fires.

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    In the days of Torness and Heysham B Power station design the CEGB had prepared extensive documents about the contribution of cable to fire and specified a maximum weight of cable per metre of ladder rack (so it wouldn't fall down) and also a maximum weight of combustible material per meter of ladder rack so that it wouldn't propagate a fire.

    It seems quite unreasonable to expect any designer to be able to adequately assess the fire risk of a bunch of cables without detailed design criteria to use and any requirement to do so is just trying to pass the buck to some mug who is less qualified to do the design but is so unqualified that he doesn't realise it.

    PS Who or what is MHCLG
  • Former Community Member
    0 Former Community Member
    "PS Who or what is MHCLG"


    Ministry of Housing, Communities and Local Government.


    Rob
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    lyledunn:

    ... if the designer specifies LSF cable for the bedrooms, for example, they might assume that risk has been reduced from what it otherwise would have been had standard twin and earth cables been used. .... but I just get the impression that we are responding in an almost knee-jerk fashion due to rightful focus on recent tragic fires.




    Couldn't agree more. If you change the cable but do nothing about all the wooden furniture, etc. that hotels insist on putting in the rooms then the improvement in the event of a fire is minimal when you take into consideration the amount of cabling you are looking at. Specifying LSF cables is only part of the solution.

    I may of course be slightly biased from working in the marine field where fire precautions are pretty robust already - on a ship you can't just evacuate everybody and wait for the fire brigade.

    Alasdair

     

  • Former Community Member
    0 Former Community Member

    lyledunn:


    Not sure what you mean by 7671 requiring risk assessment OMS, but I do understand the imperatives for designers selecting cables with better performance in fire.

    BS 7671 leaves this selection to the designer - so it is risk based.


    However, imperatives should be evidence-based and I can find nothing in the way of forensic reports detailing the contribution cabling made in real fire situations.

    Agreed - but there is a certain amount of evidence behind this - if only to say that xxkg/m of PVC cable in an escape route could produce yy/kg of smoke - but if OHLS was used it would be a lower quantity of smoke.


    For example, it would seem reasonable that cables with improved fire performance are installed say in a hotel situation but, equally, not unreasonable that they are not. Some designers, on the other hand, will  opt for the former under the pressure of perceived imperatives.

    Or under their common law duty of care to their client?


    In other words, if the designer specifies LSF cable for the bedrooms, for example, they might assume that risk has been reduced from what it otherwise would have been had standard twin and earth cables been used. Since bunching would be unlikely in the voids above bedrooms, fire safety may not have been improved one jot but it just seems that by specifying LSF the right thing has been done irrespective of cost to the client. 

    Sure - but bunching in corridors would be a different matter  - it could easily be shown that say OHLS cabling on metallic containment was readily observable as a safer solution (in fire conditions for MoE


    Dont get me wrong, I am an advocate of  meticulous consideration of fire safety measures for buildings but I just get the impression that we are responding in an almost knee-jerk fashion due to rightful focus on recent tragic fires.

    Maybe - but it is a scenario worthy of consideration by any competent designer - and in some sectors has been for many years. As a designer I'm happy to work with a client and other designers to achieve coordinated fire safety solutions for buildings that use of the tools available to enhance safety for both users of buildings and for FRS should they be called on to get people out "under smoke"

     




     

    Regards


    OMS
  • Former Community Member
    0 Former Community Member

    Alasdair Anderson:




    Couldn't agree more. If you change the cable but do nothing about all the wooden furniture, etc. that hotels insist on putting in the rooms then the improvement in the event of a fire is minimal when you take into consideration the amount of cabling you are looking at. Specifying LSF cables is only part of the solution.


    Sure - but we all have a part to play - and most items in an hotel room will have classifications for ignitability and surface spread of flame - plus detection and alarm that should ensure the limited number of occupants are roused and can evacuate to a place of relative safety (ie the corridor) - and the door to the room plays an important part in containing the fire. Selecting the correct cabling plays an important part in protecting that corridor for other occupants should that room compartment be breached.



     




     



    Regards


    OMS 
     

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    OMS:

     Selecting the correct cabling plays an important part in protecting that corridor for other occupants should that room compartment be breached.




    It certainly does. I wasn't trying to say the cable shouldn't be flame retardant. I was just trying to make the point that a holistic view is important. The biggest problem is generally not with the cables as it is easy to source flame retardant cables nowadays. A much greater problem is with other materials which claim to be 'low fire spread' but when tested are not (which rather brings back memories of the cladding on Grenfell Tower....). Of course the cables could be in that situation also but the other material is generally more of a hazard if it is not as claimed.

    My problem is with 'knee-jerk reactions' as mentioned by lyledunn; a need to be seen to be doing something and implementing a change, which is then assumed to have fixed the problem. I have no problem with this change being implemented (and am in favour of it - there is no reason why you should install cables which are flammable anywhere, and certainly not in occupied buildings - but we shouldn't think that just because we have installed flame retardant cables that we have solved all the problems.

    Alasdair

    ps On the whole I agree with all that you said, though having been in hotels where the fire alarm has gone off I generally find myself wondering, as I wander towards the assembly point, whether everyone else in the building is happy to be burned alive - you can only do so much to protect the other occupants.

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    Alasdair Anderson:



    ps On the whole I agree with all that you said, though having been in hotels where the fire alarm has gone off I generally find myself wondering, as I wander towards the assembly point, whether everyone else in the building is happy to be burned alive - you can only do so much to protect the other occupants.


    Very true Alasdair...


    Working for a previous employer and a workman while cutting off bolts in the warehouse floor inadvertently set fire to a stack of boxes (sparks flying everywhere caused a slow smoulder that then escalated rapidly). Alarm activated and everyone evacuated. During the roll call a colleague was found to be missing. Fire Brigade turn up and on entering the building find said colleague sitting in the canteen eating his sandwiches.... ?


    I believe a formal warning was issued.

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