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54 Walkable ceilings can deteriorate

Report ID: 54

Published: Newsletter No 8 - October 2007

Report Overview

A reporter has written about a complex and potentially far-reaching concern about unseen progressive deterioration in sandwich ceiling panels with mineral wool lamella cores.

Report Content

A reporter has written about a complex and potentially far-reaching concern about unseen progressive deterioration in sandwich ceiling panels with mineral wool lamella cores. They say that since the Sun Valley incident (Hereford UK 1993), in which two firemen lost their lives, mineral wool cores have been generally specified for such ceilings because of their superior performance in fire. There are, they believe, countless square metres of such ceilings in use.

The reporter goes on to say that in a more recent incident, a team of four men working in the roof space above a food processing plant fell through the ceiling when it collapsed under their weight and the weight of the load that they were carrying. One of the men was seriously injured. The ceiling was constructed of 100mm deep metal-faced sandwich panels with a core of mineral wool lamellas. The span of the panels involved was less than 2m, whereas the safe span under BS 6399 loadings should have been almost 6m.

The cause of this has been identified as progressive degradation of the mineral wool lamellas under repeated heel impacts as people walk on the ceiling. Mineral wool lamellas have near-vertical fibres of relatively brittle mineral wool and these tend to fracture as rather rigid but brittle struts locally under heel impact. As feet are never placed in exactly the same place twice, each time someone walks on the ceiling, some more fractures take place. In due course, regions of the upper face of the panel become completely delaminated and the panel loses its strength.

The panels which collapsed were on an access route which was used for routine maintenance of plant in the ceiling void. Such panels are generally classed as being suitable for "occasional access", precisely the circumstances which prevailed in the case in question. They had been in use for approximately 5 years and subsequent investigation showed that adjacent panels on this access route were in a state of incipient delamination as a result of foot traffic.

A European research contract under the acronym "ASP AN" investigated the durability of sandwich panels during the period 2002 to 2004. Panels included a range of core materials including mineral wool lamellas and several different rigid plastic foams. Subjecting the panels to repeated walking gave significant results. The mineral wool had locally lost its adhesion over an area measuring 100mm x 100mm after about 500 heel impacts whereas other core materials were relatively undamaged after up to 2,400 impacts.

There are two aspects to the resulting problem. Protecting new construction is relatively simple using, for example, spreader boards and edge protection. The industry needs to be vigilant in this respect and it is well known that a great deal of damage can be done to ceilings if they are not protected while plant and equipment is installed. The more significant problem concerns the ceilings in service which may be in varying states of degradation which is unseen and progressive. According to the reporter, no non-­destructive test is known whereby the condition of a ceiling can be established.

Comments

Composite proprietary panels are widely used and they can be required to carry live loads. Most will be entirely satisfactory but caution should be exercised. When specifying products, designers should consider the obligation to avoid hazards (so far as is reasonably practicable), before trying to control the resultant risks. Hence, the need to ask if these products should be used in situations where damage during operations could be critical?

Under CDM Regulations, the Operation and Maintenance manuals might be expected to highlight dangers from walking on panels. This might not apply to alteration work where a contractor is involved who, despite the requirements of the regulations, does not have any knowledge of the problems that could exist.

The main issue, as pointed out by the reporter, is the stock of existing buildings that may incorporate degraded panels showing no outward signs of damage but that are used as walkways. CROSS thanks the reporter for bringing this matter to their attention and it will be considered further. Advisors, contractors and facilities managers should be aware of the potential problems. In the situation where there could be latent damage, and in the absence of any other information, panels should be regarded as potentially unsafe for additional loading.


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