With their vast open spaces and often unique decor, cathedrals can
be some of the most challenging of our heritage buildings to protect. John Borns outlines the alternative approaches available.
Have you ever considered whether the fire protection of cathedrals is sufficient for buildings which may date back to the 11th or 12th centuries? Probably not, and like you, I really had not given much thought to this question until some years ago, I was asked to check the proposals for a detection system to be installed in a major cathedral. I did so not really from the point of view of it being a ‘heritage’ building, but from whether it met the current requirements. Now I have realised that a cathedral is a very different animal.
Firstly, it usually a very lofty structure with perhaps upper, triforium and clerestory levels. It has an organ, usually at an upper level, and it may well have wall hangings, wood carvings, pictures, and normally wooden pews or seating. Over the nave and aisles there is usually a considerable void, with a tower for the bells and a bell ringers’ chamber. Frequently there are unexpected openings, for example through broken glazing or open access doors to roof voids, all possibly causing drafts that affect normal point detection installations, as well as giving access to the odd pigeon!
Questions that need to be considered include the likely possibilities of a fire starting and developing unnoticed until it becomes a serious conflagration and the possible sources of ignition. Are the aisles used for exhibitions, and if so, are the displays a risk? What are the likely consequences, both to the structure and also to the means of escape, for those in the building?
Apart from the general risks from faulty electrical installation, lightning and inadequate housekeeping, those coming into the building, whether it be to attend a service, a concert or just as an interested visitor, are normally free to look around with little or no supervision. That means there is the opportunity for unwelcome visitors to cause serious damage. For example, while the main control panels can be located at the entrance used by the fire brigade, they could then be vulnerable to vandalism.
The most vulnerable areas need to be identified, as well as any specific items of value. Most relevant authorities – such as the Cathedral Chapter, English Heritage and insurers – will hope to achieve a detection system covering all areas to a BS 5839-1 L1/P1 design. In reality, however, there will always be small, hard-to-access corners of a cathedral that are just not cost effective to cover.
There is then the issue of addressing the risks without affecting the aesthetics of these grand buildings. Radio linked systems can be a suitable alternative in highly decorative or ornate buildings, such as St Chad’s in Birmingham. These systems also have the advantage of being quicker to install than hard wired ones. And although even hard-to-reach detectors can be accessed for testing maintenance by means of pole-mounted equipment, radio linked ones need to have their batteries changed too, and this can be difficult if they are not easily accessible.
With such lofty buildings, smoke from a fire rises and cools to a point where it tends to stratify, so the detection unit needs to be at or below this level. Unfortunately this can vary from day to day and even hour to hour. However, prior to preparing a draft specification, a hot smoke test usually indicates an approximate level which can at least form the basis of a design. I say “hot” smoke test as, from experience, I have found smoke generated from the normal pellet test fails to rise sufficiently and is not a satisfactory representation of smoke movement in actual fire conditions
The first systems installed in such buildings were point detection, with beam detectors where appropriate. But with the location of the point detectors at high levels, there was little prospect of rapid detection, if at all, of any fire at ground level. Beam detectors have been installed to cover the nave areas and aisles, but are vulnerable to false alarms from shimmers of light caused by windows at high levels. In addition, both beam and point detectors, when visible from the ground, were not always considered aesthetically acceptable by those who are responsible for such buildings. A more reliable system with a lower visual impact was needed to achieve the compromise that is invariably required.
Air sampling
Recently there have been developments, particularly in aspirating, or ‘air sampling’, detection systems. These have proved suitable, together with point detection in those areas where the aesthetic consideration is not so important and the height permits them.
It is normally possible to deploy the larger piping of an aspirating system either at the triforium and/or the Clerestory level, with capillary tubing extending from this over the edge and protruding into the nave, or at high level concealed above a ledge or other projection. Even if this is not practicable, there are frequently a number of cable runs at high level where the main tubing can be fixed and, if necessary, coloured to match the background with clear capillary tubing brought down to the lower, detection level. Excessive draft conditions in the tower and roof voids invariably call for an air sampling unit, and the coverage from this can be extended to the bell and ringers’ chambers.
The main problem when considering such a system is the location of the detector unit. All aspirating units incorporate a small fan continually drawing air through the piping back to the unit. The noise from these can become an issue, particularly if they are positioned near, say, the organist who invariably has extremely sensitive hearing! But it’s possible to enclose the unit within a semi- sound proofed cabinet, and this has had to be done on a number of occasions.
As with all equipment, periodic inspection and maintenance is necessary. So although it may be ‘convenient’ to hide these units in high level voids, such as above the aisles, in the long term this can become anything but convenient in terms of access, which may then lead to inadequate servicing.
Detection cover in those areas of the cathedral not normally accessed by the public can, with the agreement of English Heritage, the cathedral architect and the cathedral Chapter, be dealt with by point detection. This also applies to the small chapels which frequently seem to be outside the limits of an aspirating unit. As with air sampling tubing, point detectors can be coloured to match their background.
Once suitable contractors have been appointed, it is necessary to supervise the work as it proceeds. Any deviations from the agreed design and equipment layout invariably requires full appraisal by the authorities before any alterations are executed, and this may lead to delays. It therefore becomes necessary to ensure that contractors always have some area where they can continue to work should they be held back in this way. After the equipment is installed, commissioning and acceptance tests – including a further hot smoke test – should be carried out.
The majority of recent installations in both cathedrals and other large heritage buildings follow much the same pattern of protection as above. But we cannot stand still, and insurers particularly are concerned not only about the possible loss and damage due to fire, but also to vandalism and theft.
Can both fire detection and security be combined? There have been demonstrations of CCTV systems that are effective in well lit commercial buildings. Having initiated tests on this type of equipment, I have to say there is some way to go for their application in cathedrals, due mainly to the problem of the low light levels and the inadequate contrast between the smoke and the stonework. Also, for optimum smoke detection, black and white cameras provide the highest resolution but in terms of security, colour images offer better identification of those being surveyed.
There are also further developments within the industry, some of which, if proved successful, could be the best thing since sliced bread! In the nearer future, I am facilitating a new set of tests of CCTV detection later this month at Lincoln Cathedral, which will demonstrate whether this type of technology has been developed sufficiently for applications in these buildings.
John Borns is a fire engineering consultant.
