Observations and comments on the installed system
4.1 General
Unfortunately the fire-damaged area had been cleared and the wall and ceiling linings replaced. An inspection of the adjoining compartments, which are understood to be of similar design, was made and photographs of the fire-damage area taken by hospital estates staff at the time of the fire were inspected.
4.2 Ceiling design
The basic design of the ceiling system appeared to be broadly similar to the system described in the BRE report CC 205235, i.e. 9mm Asbestolux panels screwed to the underside of a steel grid. In the room next to the corridor, the main runners of the grid were T-sections approximately 38mm x 38mm, which were located at nominal 600mm centres, with cross tees, approximately. 25mm x 25mm, at nominal 600mm centres. The main runners were not suspended directly from the structure above, but secured to galvanised steel I-sections, approximately 75mm deep x 50mm wide, located at approximately 1200mm centres. The I-sections appeared to span from wall to wall, with no hangers to the structure above.
These installed ceilings do vary somewhat from the system described in the BRE report CC 205235, the main difference being that the I-sections that the main runners are secured to, are not supported at regular intervals, but appear to span from wall to wall.
4.3 Ceiling supports
If the I-sections are supported by hangers at maximum 1.5 metres, or fixed to beams at maximum 1.5 metres, we are of the opinion that if the design of the installed ceiling system was tested, without any unsealed service penetrations, etc., we would expect the ceiling system to prevent the collapse of the lattice trusses above for at least 30 minutes, when tested in accordance with BS 476: Part 23:1987. However, if the I-sections are unsupported for spans of more than 1.5 metres, we are of the opinion that there may be excessive sagging of the ceiling system in the event of a fire, which may lead to premature collapse. In this case, we guesstimate that the likely fire performance of the ceiling may be less than 30 minutes.
4.4 Screw fixings
It was noted that the screw fixings were generally located in the correct positions, but that there were locations where the screws were more than 50mm from the corner of the panel. This can lead to the corner of the panel curling away from the grid, and allowing the fire to have direct access to the cavity. In addition, if screws are located within 10mm from the tile edge, or within 25mm of the corner of the tile, the tiles may crack when exposed to fire.
4.5 Light fittings
We understand that light fittings were generally surface mounted. This is normally acceptable, providing the fitting is secured through the ceiling tiles to a grid member that has additional support above the fitting, and any cables penetrating the tiles are kept to a minimum, with any gaps sealed with an intumescent mastic.
4.5.1
It is understood that recessed light-fittings are not used, but if it is found that some have been fitted, a suitable fire-rated light box must be installed above the fitting.
4.6 Gaps and holes
It was noted that there were some circular holes, about 75mm diameter, in the tiles, which had simply been taped and painted over. It is recommend that the tape is removed and that a patch of Supalux, or similar, is screw-fixed over the hole, either over the top or to the underside of the tile. The patch must overlap the main tile by at least 25mm on all sides.
4.6.1
It was noted that there were gaps around the edges of the ceilings. These should be sealed with an intumescent mastic.
4.7 Ductwork and vent grilles
It was noted that there were various steel ventilation grilles mounted in the ceilings, which were connected to a steel ventilation ductwork system above the ceiling. We also understand that there may have been similar vents in the area of the fire. These will permit very rapid fire ingress into the ductwork, and into the ceiling void. It is probable that this will lead to the ceiling grid and the ductwork weakening and deforming, thus creating excessive stresses on the ceiling tiles, and the system collapsing before 30 minutes.
4.7.1
We are also concerned that the ductwork is insulated in places with a plastic foam, probably polystyrene. A material not specified in the original design for encasement of ventilation ductwork. This could lead to large amounts of thick, toxic fumes being emitted in a fire, and also fire spreading rapidly along the outside of the ductwork. Fire may therefore be spread rapidly from one compartment to another either within or outside the ductwork. We therefore recommend that the ventilation of the building is reconsidered with a view to either: -
a) removing the vent grilles altogether, or
b) replacing them with intumescent grilles, or
c) encasing the full run of ductwork with a suitable fire protection system.
d) In cases b) and c) additional hangers are required at the inlet to the ductwork, to ensure that there is no loading on the ceiling system from the ductwork.
4.8 Partitions, cavity barriers, and external walls
The inspection was mainly concerned with the suspended ceilings, but the following points were noted concerning the partitions, cavity barriers, and external walls.
4.8.1
The BRE report 205235 recommended that the studs be extended to the slab above, and that adequate cavity barriers are fitted in the ceiling void above the partitions. As far as could be seen, this has not been done, apart from some cavity barriers being fitted in some areas. However, it was also noted that services appeared to penetrate the cavity barriers that were installed, without adequate protection or additional support, and therefore it is likely that if a fire started in the ceiling void, or gained access to the void via ductwork, or gaps in the ceiling, etc., as discussed above, the fire may still spread to the next compartment.
4.8.2
As the framing of the partitions is only secured to the underside of the ceilings; this may lead to a premature failure of the ceilings and/or the partitions in certain fire situations.
4.8.3
As stated above, the site visit was mainly concerned with the installed ceilings, but similar care should be taken with the internal partitions with regards to the sealing of any areas where the partition lining is breached, for example at service penetrations. The BRE report CC 205235 pointed out various other concerns such as the use of a plastic foam insulation in the external wall cavities. Such foams can lead to excessive amounts of toxic fumes and flaming if fire is allowed to penetrate the wall linings via service penetrations, weaknesses around window or door reveals, etc.
©2004 Oxford Method Royalties Management Group