Fire detection for London warehouses and industrial units

Because of stratification. Smoke rises only until it reaches air of the same temperature, and then it spreads sideways instead of continuing up. In a warehouse with a hot layer of air under a sun-baked roof, smoke from a fire at floor level can flatten out well below the ceiling and simply never reach the detectors, or reach them long after the fire has developed. Adding more point detectors at the same height does not fix it, because the problem is the height rather than the spacing. BS 5839-1 sets mounting height limits by detector type for exactly this reason, and above them the answer is a different technology.

Usually optical beam detection or an aspirating system, and which one depends on the building rather than on preference. A beam detector projects across the space and looks for obscuration, which suits a long clear span and is comparatively economical to cover a large volume. An aspirating system draws air continuously through a pipe network to a detector in a cabinet, which suits dirty or cold environments and can be far more sensitive, and it has the practical advantage that the detector itself is at ground level where somebody can actually service it without a scissor lift.

Considerably. Racking creates vertical channels between the pallets, and a fire in a lower level draws air up those channels and climbs much faster than the same fire in open storage. The consequence for detection is that a system watching only the roof void may be watching the wrong place, and the consequence for suppression is that in-rack provision exists precisely because ceiling-level sprinklers cannot always reach a fire buried inside a block of racking. How high you stack, and what is on the pallets, changes the answer more than the floor area does.

Yes, and it is a design question rather than a maintenance one. Dust and diesel particulate trigger optical detection for the same reason steam does in a kitchen: they scatter light. An aspirating system with appropriate filtration is the usual answer in a genuinely dirty environment, because the sampling is continuous and the filter sits where it can be changed. Beam detectors can also be specified with sensible alarm thresholds and drift compensation. What does not work is leaving a zone isolated, which is what we usually find, and which means the largest space in the building has nothing watching it.

It depends on the building, the insurer and what is stored, and it is not something to answer from a desk. Where a system is required it is designed to BS EN 12845, and the storage classification and the height you stack to drive the design density and therefore the water supply, which is usually the largest single cost. That is why the first questions on a sprinkler survey are what is on the pallets and how high they go, rather than the floor area. We survey, design and install, and we can also just tell you that what you have is adequate, which is sometimes the answer.