Timber frame construction sites should not be any more prone to serious fires than projects using ‘conventional’ materials, say Peter Jackman and Chris Houchen. Following investigations into the Beaufort Park fire in Colindale, they describe a new scheme to reduce such a fire happening again.
Construction has never been risk-free, either in terms of health and safety nor in respect of things going wrong with the building process itself. The most common reason for failure during construction is premature collapses, caused by the uncured material not achieving full strength, or due to collapse of any temporary shuttering or scaffolding.
Fire, however, should not be forgotten. There have been some high profile fires during construction, not least at Broadgate and Minster Court, both in the City of London and the latter being the intended home of the insurance industry! Both of these fires were constructed in conventional materials and resulted in massive financial losses, demonstrating just how vulnerable buildings are until compartmentation has been fully completed and the protected routes put in place.
The Colindale fire last year – which resulted in the loss of three six-storey timber apartment blocks – once more reinforced the message that uncompleted buildings can be vulnerable to fire. Nobody would deny that a large unclad timber frame is in the ‘more vulnerable’ category, along with composite panel buildings, but there are hundreds of timber framed buildings and large insulated sheds built every year without experiencing fire during construction. It is not the combustibility of the basic material that is the cause of fire, it is the processes that go on during construction that produce the hazards. With a construction form where the basic structure is timber, the likelihood of the damage being disproportionate is high, but the likelihood of a fire occurring is no different than that for almost any other site.
A review of the most likely causes of fire on a construction site would identify arson, hot working, smoking or heating appliances. A match or even a lighter will rarely, if ever, have sufficient energy to ignite the timber structure or any of the wood based linings. These will normally only get involved if, for example, the petrol for the dumper truck is liberally spread around before hand. Again, sparks and hot grinding wheels will fail to ignite structural timber, but they can ignite polymeric insulation, paper or packaging which is normally to be found on any site. As a consequence, the main cause of fire during construction must, at the end of the day, come down to complacency: “we have not had a fire before, why should we have one now? Remove complacency and over confidence and most fires can be eliminated. The need to eliminate complacency grows as the vulnerability of the construction to disproportionate damage increases. Such is the case with timber frame.
Aftermath
In the aftermath of the Colindale fire, IFC Certification Ltd was contacted by the design consultants of a major timber frame company, together with a leading developer, to produce a scheme designed to eliminate fire incidents during the construction of timber frame buildings. The construction process embraces a number of ignition risks, from plumbing through to grinding, welding and temporary heating. Of course, an unfinished house presents an ideal target for those wishing to carry out malicious arson, as there are normally sufficient materials lying around on any building site to start a serious fire. IFC Certification’s response was to investigate how a quality system operating on a building site could reduce the risk of accidental, or deliberately initiated ignitions.
Framework
With timber frame construction, there are obviously a number of factors that can lead to such disproportionate damage. For quite lengthy periods the frame is left unprotected while other trades are installing, for example, wiring, pipework and insulation. Processes that create heat during this phase need to be controlled and monitored and while everybody is generally aware of the principle of hot work certificates, on a construction site sometimes this is overlooked in the ‘heat’ of the moment.
Partially completed buildings almost invite arson. There is also, inevitably, a storage problem which needs to be managed, both for new materials being delivered to site and the rubbish and waste that needs to be removed from it. Both provide the arsonist with fuel. Sadly, the likelihood of arson is often related to socio-economic factors and the construction team need to be aware of this right from at the onset of the build process. Good security and surveillance are the most important way of controlling malicious arson.
The new scheme takes a holistic view of the construction process which, if implemented properly, should make the risk of a serious fire on a timber frame site no worse than that on a site using more traditional construction, and hopefully better. From the outset it was recognised that it was probably impractical to produce a site free from any fire risk, without the measures being introduced to control complacency becoming a real impediment to the efficiency of the construction process. This was the challenge faced by IFCC.
The quality scheme generated had two objectives:
– to reduce the likelihood of ignition by ongoing risk assessment against good practice guidance, and
– to limit the magnitude of any fire damage that could occur, as measured in terms of size, or monetary value.
The first of these objectives identifies that malicious arson from outside, or even from internal sources, can be a major cause of ignition. All projects start off by an analysis of local crime statistics and a review of the press to establish whether there has been any underlying resistance to the development. The outcome of this process will identify whether the potential for arson is high, medium or low, and this sets the base level for a number of subsequent factors.
The effectiveness of any site fencing, both in respect of its ability to prevent entry and/or to restrict vision, can be rated as low, medium or high, and this interacts with the levels of surveillance needed during construction. The control of people entering and leaving the site, including delivery drivers, can be assessed against fixed criteria because there is a huge difference between 24/7 patrolled surveillance and remote CCTV monitoring.
Control of storage is also important and is directly related to:
– the volume of any combustible materials
– the proximity of these materials to the site boundary
– the proximity to these materials to the buildings, and the duration for which they are in that position
– the combustibility and susceptibility to radiation of the nearest building facade.
Risk based
Under the scheme, it is possible to have high volumes of stored combustibles even close to a building. But in such cases, the site surveillance would need to be of the highest level and the control of potential ignition sources all but eliminated. In order to achieve this, the levels of inspection would probably be commensurately high. All of these measures should reduce the potential for ignition of the stored material and the consequence of it. A good scheme is the one which achieves the balance between good practice and good control.
The overall risk, particularly in respect of the potential property loss, is generally dominated by the area and volume of the timber frame building. The risk of unacceptable losses goes up with the increase in a building’s footprint or its height. Again, contractors or developers have options: they can accept that a large footprint and/or high build results in a higher risk situation, so that the inspection and ongoing site management are increased commensurate with this risk. Or the footprint can be sub-divided as building work progresses, by means of fire resisting construction, to bring the risk category down. The same applies to height. Horizontal barriers need to be installed early, especially any cavity barriers which are capable of compromising any horizontal compartmentation.
Compartmentation is, however, a waste of time if external fire spread – from window to window – can short circuit the protection it provides. Control should therefore be exercised over the nature of the external surfaces, particularly where there is a courtyard scenario or where there are ‘steps and staggers’.
The ‘Build Timber Frame Safely’ scheme is being piloted in Kent. It consists of inspection and management by the contractor, overseeing inspection by IFCC nominated and trained inspectors at designated intervals, and is ultimately audited by permanent staff of the certification body, at intervals dictated by the risk. The frequency of all levels of inspection forms part of the approval process. The proof of the effectiveness of the scheme is, of course, dependent upon the number of properties that can ultimately be handed over for sale, the target being 100%, and nothing less.
It must be stressed, however, that building in timber is not a major risk. It just has to be acknowledged that timber buildings are very vulnerable to disproportionate damage at key stages during construction. Anybody who has spent time in the USA will have seen condominium (apartment) blocks built out of timber frame elements left unclad for weeks on end and they rarely, if ever, experience a fire of the Colindale magnitude. Timber, while not being conventional construction in the UK, is conventional throughout North America and Northern Europe. They neither have the fear, nor the experience that we have had, mainly because they have learnt not to take risks. The IFC Certification scheme restricts the abuse that could be experienced in the UK due to our lack of familiarity with the material.
Fires in other building types are not uncommon. Concrete is the indigenous material in the Middle East, but that has not prevented the occurrence of two serious construction fires in Dubai this year, sadly causing death and injury and not just property damage. The scheme, while having been instigated in response to a timber frame fire, will ensure a lower frequency of fire in any type of construction. Risk assessment is now used extensively to control the way we use the built environment, so why not use it during construction?
As is the culture within IFC, the scheme has been produced at the request of the industry and by people with construction industry experience and a real empathy with timber. After all, what other certification body has three corporate members of the Institute of Wood Science within its senior management.
Peter E Jackman MIFireE IEng FBEng AIWSc is technical director and Chris Houchen BSc. AIWSc, AIFireE associate director of International Fire Consultants. www.ifccertification.com
FAR FROM COMPLACENT
In May 2007, two reports into the fire at a residential development in Colindale concluded that, at the very least, better fire precautions were needed in the construction of timber frame buildings. The fire destroyed a six-storey residential block in around nine minutes. One of the reports – from the Fire Protection Association – even questioned whether timber frame structures should be used for high rise construction at all.
Speaking exclusively to FSE, chairman of the UK Timber Frame Association, Stewart Dalgarno, said that every construction method incurred some risk, and each site required different risk managements procedures and processes. “I totally reject the view that timber frame is not suitable for high rise construction. High rise and high density construction is a fact of life – it carries a risk regardless of the materials being used.”
But as far as defending the status quo, that’s as far as Mr Dalgarno goes. He says that his industry has learned lessons from the Colindale fire and the subsequent investigations into it, and is addressing some of the issues involved. This includes the establishment of the Build Timber Frame Safely scheme described on these pages. The Association is also considering earlier compartmentation in the construction process. “It’s not a significant cost issue, just a change in design and building culture.”
What may be more of a cost issue is treating timber frame buildings for fire retardance. Although, of course, there are treatments available for timber products, their application is not yet cost-effective for the large volume processes that would be needed for timber frame buildings. So the industry is also examining ways of improving the fire resistance of its building materials, and is working with fire retardant treatment suppliers.
The timber frame industry is also making an effort to engage with the fire safety industry at large. Mr Dalgarno recently met up with the Fire Protection Association, the authors of the report into the Colindale fire, and is also liaising with the Health & Safety Executive and the London Fire Brigade. The Association has also appointed a full time fire advisor, Dave Berry, a fire engineer and member of the Institution of Fire Engineers who sits on a number of British Standard committees on building design standards.
“These initiatives show that we are serious about developing timber frame construction as a viable and safe construction process,” Mr Dalgarno concludes.
