The LWF Blog
Facilities Management & Fire Safety – Sprinkler System Design Principles – Part 9May 26, 2017 11:17 am
In this blog series for those who work in Facilities Management and have an interest in or responsibility for Fire Safety, we have been looking recently at Sprinkler System Design Principles. We established that there are three types of building classification to be taken into account when designing and installing a sprinkler system – Light, Ordinary and High Hazard. We also looked at how the Ordinary and High Hazard categories could be further divided, as within BS EN 12845, into subcategories. In part 9 of this series, we’re going to continue discussing the types of High Hazard occupancies.
The second of the High Hazard Categories is ‘High-piled storage hazards’. This description commonly indicates warehouses and the definition varies according to how the stock is stored and, of course, what type of product it is. The goods themselves are classified into four different categories which indicate how they would interact with fire.
The minimum density (mm/minute) and AMAO (Assumed Maximum Area of Operation) are tied in to the storage height. Some products, flat paper is one of them, only fall into the High Hazard category when the storage height exceeds a certain level. Below that, they would be classed as an Ordinary Hazard. Different types of product have different storage height limits for each classification level.
In the case of high storage level and therefore High Hazard level occupancies, ceiling sprinkler outlets may not be considered sufficient and additional intermediate sprinklers within the storage racks themselves might be necessary.
Bearing all this in mind, it is essential that the correct classification for the occupancy is ascertained before the sprinkler design is commenced. Once classification is achieved, the first stages of the design, such as the type of water supply and the size of the pipework can be decided upon.
In the case of High Hazard properties, it may be the case that the local water authority provision is unable to provide the necessary flow rate and in these cases, a tank and a pump (or multiples thereof) will be required. The minimum required flow rate determines the rating of the pump and as the system must be capable of supplying water for a specified amount of time, both the hazard classification and rating of the pumps will determine the capacity of the water tanks.
The required amount of water must pass through pipes in the necessary amount of time and for this to be achieved, the pipes have to be the correct size too.
Hydraulic calculation (often computer aided design) can be the best route to take in cases where the design is complex or in the case of High Hazard occupancies, as it can pinpoint ways that the installation can proceed, fulfilling all necessary safety concerns, in a more cost-effective way. The schedule of pipe sizes in BS EN 12845 may also be used, which may work out more expensive and less ‘tailor-made’ but might make changes to the system in the future easier to achieve.
In Part 10 of this series, we’ll look in more detail at water supplies for sprinkler systems. In the meantime, if you have any queries about your own facilities or wish to discuss this blog series, please contact Peter Gyere in the first instance on 0208 668 8663.
Lawrence Webster Forrest is a fire engineering consultancy based in Surrey with over 25 years’ experience, which provides a wide range of consultancy services to professionals involved in the design, development and construction and operation of buildings.