GB2097046A

GB2097046A - Fire-resistant grilles

Info

Publication number: GB2097046A
Application number: GB8112123A
Authority: GB
Original assignee: MANN MCGOWAN FABRICATIONS Ltd
Current assignee: MANN MCGOWAN FABRICATIONS Ltd
Priority date: 1981-04-16
Filing date: 1981-04-16
Publication date: 1982-10-27
Also published as: GB2097046B

Abstract

A fire-resistant grille 10 comprises an assembly of slats 11 formed of intumescent strips 13 each contained in a PVC sheath 12. The slats 11 are spaced by PVC blocks 18 through which pass tie rods 20 which are clamped at their ends to steel strips 16 by nuts 22. The outer surface of each strip 16 is covered by a PVC- sheathed intumescent strip 16. <IMAGE>

Description

SPECIFICATION Fire-resistant grilles This invention relates to fire-resistant grilles for location in ductwork in a building or in an aperture in, for example, a wall or door of a building.

In the construction of buildings it is usually necessary to provide ducts for the passage of air or services and, particularly in those in which inflammable materials are handled, it is often also necessary to provide apertures through parts of the structure such as walls, partitions and doors so as to afford ventillation under normal circumstances. However, to prevent the spread of flames, hot gases and smoke through the duct or from one side of the aperture to the other it is essential that the duct or aperture should be closed on the outbreak of fire. A known method of doing this is to locate in the aperture a grille formed of slats of intumescent strip material.

Such a material is usually based on a metal silicate such as hydrated sodium silicate, and lack water-resistance and mechanical strength. As other intumescent materials, even though waterresistant, lack mechanical strength it is customary to enclose any intumescent material in a thermoplastics sleeve, typically of PVC, which provides protection against chemical attack as well as adding mechanical strength. The slats formed of such intumescent strip material are spaced by PVC spacing blocks which are apertured, as are the slates, to allow the passage of supporting rods which have nuts at each end so that the grille assembly is held in compression and forms a strong and stable structure under normal conditions.The separation between the slats of the grille is a compromise between the proximity desirable to ensure speed of closure on the outbreak of fire and the separation necessary to reduce resistance to ventilating air flow under normal conditions: a distance of 8mm is the normal compromise. When the intumescent strip material forming the grille is exposed to heat the sheathed intumescent material expands and stretches the softened PVC casing. The spaces between the slats thus become filled and the aperture in which the grill is located is closed.

Continued exposure of the grille to heat causes the PVC to pyrolise and degrade so that the aperture is finally closed by what is effectively a continuous self-supporting slab of hard expanded foam.

The above-described grille is effective up to a size of about 400 by 400mm. However when the same construction is used for larger sizes sagging or buckling of the slats occurs during the initial stages of fire when both the PVC and intumescent material soften and flow. This sagging can cause gaps or weak points near the top of the grille or between the top of the grille and the upper edge of the aperture in which the grille is located, thus allowing the fire to break through.

According to the present invention this undesirable effect of sagging or buckling is overcome or alleviated by the provision of a fireresistant grille comprising a set of slats formed of intumescent material, means to maintain the slats in spaced relationship, at least one of the outer slats being reinforced by a support of rigid, noncombustible material, the exposed, outer surface of which is covered by a layer of non-combustible insulating material.

The slats are preferably formed of strips of intumescent material contained within a thermoplastics sheat and the means to maintain the slats in spaced relationship comprise spacer blocks interposed between adjacent slats, the slats and blocks being apertured to receive tie rods which terminate at each end in securing means which cooperate with the outer slats to hold the assembly in compression.

The reinforcing support which remains rigid at elevated temperatures when the slats are tending to sag and buckle is preferably secured, when the grille is located in an aperture, to the upper edge of the aperture so that the grill is suspended rather in the manner of a curtain from a rail. If the other outer slat is similarly reinforced by a rigid support the whole grille structure becomes selfsupporting under both normal and fire conditions.

A further advantage of having both outer slats reinforced is that the tie rods may be secured to one of the supports at each end which will clearly result in a more rigid grille than if the tie rods are so secured at only one end. Where the grille is mounted with the slats running vertically it is virtually essential to have both the outer slats reinforced.

The reinforcing support is preferably of steel, and of strip or plate form, and it is because such a material is a good thermal conductor that it is necessary for the surface of the support which is not juxtaposed with the slat to be shielded by a layer of non-combustible insulating material to help to keep the reinforcing support cool.

Although the insulating material may be a nonintumescent material such as mineral fibre, rock wall or foamed asbestos it is preferably an intumescent material which not only expands under heat to seal any gap between the grille and the edge of the aperture but also emits water during such expansion which has a cooling effect; conveniently the intumescent material may be in the same form as in the slats, that is sheathed in a PVC casing so that the reinforcing support is sandwiched between the outer slat and a further length of PVC-sheathed intumescent strip material.

In an alternative embodiment the support is sandwiched between two layers of intumescent material both contained within a thermoplastics sheath.

The longitudinal edges of the reinforcing support should be inset from the edges of the outer slat so that when the intumescent material expands it shields the edge of the support from the exposure to the fire and thus reduces heat transmission from the exposed to the unexposed side of the grille. The reduction in lateral heat transmission is enhanced if the support is formed by two strips arranged side-by-side in the same plane with a medial gap therebetween. The same effect of reducing lateral heat transmission may be achieved to a lesser extent by removing areas of the support. As with the use of two separate strips the thermal capacity of the reinforcement is reduced which is beneficial: another method of reducing thermal capacity is to employ a thin strip which is longitudinally corrugated or ribbed to increase its stiffness.

Where the reinforcing support is a material having a large coefficient of thermal expansion it is preferably shorter than the outer slat in order to allow for thermal expansion which otherwise might cause exposure of the ends and buckling.

Where a large aperture has to be fitted with a grille it is often preferable to modify the abovedescribed structure by combining two or more grilles in which both the outer slats are reinforced.

Because of the intermediate reinforcing supports such a combined grille is structurally stronger and also easier to produce and instal.

Although the present invention may be carried out in a variety of ways one particular embodiment thereof will now be described, by way of example only, with reference to the accompanying diagrammatic drawings in which Figure 1 is an isometric view of a portion of an intumescent fire-resistant grille according to the present invention; Figure 2 is a broken-away part section on the line A-A' of Fig. 1; and, Figure 3 is a similar section through a modification of the construction of Fig. 1.

As shown in Figs. 1 and 2 an intumescent fireresistant ventilator grille and damper 10 1500mm high and 800mm wide consists mainly of a series of slats 11 formed of an intumescent strip material comprising a hollow oblong section PVC sheath 12 containing an intumescent material 13 known as "Palusol". The top slat 11 a and the bottom slat (not shown) are each juxtaposed with a reinforcing 18 gauge steel strip 14, the longitudinal and end edges of each strip 14 being inset from the corresponding edges of the juxtaposed slat 11. Each steel strip 14 is in turn covered by a further "Palusol" covering strip 16 and is adhesively secured to the two layers of identical "Palusol" strip between which it is thus sandwiched.

The assembly of slats 12 is maintained in spaced parallel relationship by columns of PVC spacing blocks 18, the blocks and slats being apertured to receive tie rods 20 which are terminally threaded to receive nuts 22 which engage a respective one of the strips 14 and are shrouded in the strips 16: the whole assembly is thus maintained in compression and forms a rigid structure under normal conditions. If the tie rods 20 of the end columns of spacing blocks 18 are inset by 20mm and the tie rods 20 of the intermediate columns positioned at intervals of not more than 200mm, sagging of the slats 12 is minimised during the onset of fire and during the period in which both the PVC and intumescent material have softened and the latter has not yet formed a hard foam slab.

The framework of the grille 10 is completed by two transverse frame members 24 which are secured to the end faces of the slats 11 and strips 16 by PVC cement.

The grille 10 is secured in an aperture by means of nails, screws or bolts (not shown) passing through the upper steel strip 14 and preferably along a line near each edge thereof, the apertures in each line being at 300mm centres with those on one side being staggered with respect to those on the other side. The advantage of the double row of fixings is, of course, that even if the row of fixings on the side exposed to fire gives way the grille 10 will still be held by the row on the other, unexposed side.

In an alternative embodiment the grille may be secured in the aperture by beading.

It is essential that the grille 10 should be secured at its upper edge so that the steel strip 14 may perform its role of supporting the grille 10, rather in the manner of a curtain rail, while the slats 11 are being softened by fire; and also so that the "Palusol" covering strip 16 is mounted in close proximity to the upper edge of the aperture to ensure that no gap forms between the aperture and the strip 14.

When a grille 10 of the above-described construction proves difficult to produce in one piece it may be made in two or more sections, the sections being bolted together by bolts engaging the steel strip at the lower edge of the upper section and the steel strip 14 at the upper edge of the lower section. The interposed covering strips 16 are thus clamped between the two steel strips.

The bolts are disposed between the tie rods 20 and the sides of the sections and between each neighbouring pair of tie rods 20; the bolts may be set along the centre line of the strips 14 or set near the edges in a staggered formation.

In Fig. 3 is shown an alternative arrangement of securing together an upper grille section 30a and a lower grille section 30b. The grille section 30a has a construction similar to that of the grille 10 and the section 30b is also similar except in that the upper covering strip 16 is omitted so that only a single "Palusol" strip 16 is clamped between the steel strips 1 4b, 14a by means of the bolts 32. The heads and nuts of the bolts 32 may be recessed into the slats 11 b, 1 1 a respectively.

Claims

1. A fire-resistant grille comprising a set of slats formed of intumescent material, and spacing means to maintain the slats in spaced relationship, at least one of the outer slats being reinforced by a support of rigid, non-combustible material, the exposed, outer surface which is covered by a layer of non-combustible insulating material.

2. A grille as claimed in Claim 1, in which the slats are each formed of a strip of intumescent material contained within a sheath of thermoplastics material.

3. A grill as claimed in Claim 1 or 2, in which the or each support is formed of steel.

4. A grille as claimed in Claim 1,2 or 3, in which said means comprise spacer blocks interposed between adjacent slats, the slats and blocks being apertured to receive tie rods which terminate at each end in securing means which cooperate with the outer slats to hold the assembly in compression.

5. A grille as claimed in any preceding claim, in which both outer slats are reinforced with a support.

6. A grill as claimed in Claim 5 as appendant to Claim 3 or 4, in which each tie rod is secured at each end to a respective one of the supports.

7. A grille as claimed in any preceding claim, in which said non-combustible insulating material is intumescent material.

8. A grill as claimed in Claim 7, in which the intumescent material is sheathed in thermoplastics material.

9. A grille as claimed in any preceding claim, in which each longitudinal edge of the or each support is inset from the corresponding edge of the adjacent outer slat.

10. A grille as claimed in any preceding claim, in which the or each support comprises two laterally spaced, co-planar strips.

11. A grille as claimed in any preceding claim, in which the or each supports is longitudinally ribbed or corrugated.

12. A grille as claimed in any preceding claim, in which the or each support is shorter than the adjacent outer slat.

13. A grille as claimed in any preceding claim and additionally comprising two transverse frame members.

14. A grille as claimed in Claim 1 and substantially as herein described.

1 5. A fire-resistant grille substantially as hereinbefore described with reference to Figs. 1 and 2 of the accompanying drawings.

16. An assembly of grilles as claimed in any preceding claim.

17. An assembly as claimed in Claim 16, in which the adjacent supports of neighbouring grilles are secured together with the interposition of a single layer of intumescent material.

18. A grille assembly substantially as herein described with reference to Fig. 3 of the accompanying drawings.

19. A grille as claimed in any one of Claims 1 to 15 or a grille assembly as claimed in any one of Claims 16 to 18 when secured in an aperture by securing means passing through at least the upper support near each longitudinal edge thereof.

20. The features as herein disclosed, or their equivalents, in any novel selection.