Lawrence Webster Forrest (LWF), Fire Engineering and Fire Risk Management Consultants
Lawrence Webster Forrest (LWF), Fire Engineering and Fire Risk Management Consultants



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Lawrence Webster Forrest
Legion House
Lower Road
Kenley
Surrey
CR8 5NH

Tel: +44 (0)20 8668 8663 Fax: +44 (0)20 8668 8583
E-mail: fire@lwf.co.uk

Fire Engineering Design and Risk Assessment - Hot Smoke Tests - Part 22

Posted by LWF: 15/06/2017 16:15

In this blog series for Architects and others in the building design business, we have been looking at fire and smoke ventilation. In Part 21 of the series, we talked about the reliability and performance of a given design. In this blog we will give an overview of Hot Smoke Tests and how they are used.

There is currently no requirement for hot smoke tests in the UK and although their use has been touched upon in many international codes and papers, they are not in regular use throughout most of the world. Hot Smoke Tests are mainly to be found in Australia where their use is commonplace and there is an appropriate test standard – AS 4391 : 1999: Smoke Management Systems – Hot Smoke Test.

AS 4391 is the only hot smoke test standard available and its intention is to assure the correct performance of a smoke management system. The standard does not apply to all systems, but provides tools whereby inconsistencies or uncertainties can be resolved in suitable systems.

There are also limits that must be worked within in order to adhere to the test laid out in AS 4391 which is unsurprising, due to the nature of testing with real fire situations. For instance the test fire size must be limited to maximum safe ceiling temperatures.  For all situations which fall outside of the guidance, real fire testing would be inappropriate and undesirable.

The design calculations and equations contained within the standard are based upon historic tests and conservative limits.

Because a hot smoke test is designed to test the system in a fully working state, the whole system must be installed and operational prior to operation of the test.

Smoke control systems also usually rely upon the air-conditioning system to provide make-up air and so the air conditioning system must also be up and working. In addition, conditions such as windows, doors, walls, ceilings and other barriers all affect the progression of a fire and the smoke control system and so these must be in place before the test is executed.

Fire produces a buoyant smoke plume which rises above the source of the fire until it reaches the a ceiling or a roof in a confined area.  Stratification occurs when the buoyancy forces lose momentum before reaching a ceiling or roof. The standard indicates that the size of the fire used for hot smoke tests should be sufficient to overcome stratification, but no more. 

A method statement must be prepared before a test, including theoretical analysis of temperatures in the plume. The test fire itself must be safely contained and the tracer-smoke must be non-toxic.

While the fire must be as ‘clean burning’ as possible to avoid damage to the building’s fittings, the hot plume which will rise from the fire will require ‘doping’ in order for it to be visible during testing. However, the use of such a test or doping to ensure the plume is visible must not be used to assess tenability of conditions or safe egress from a building.

In Part 23 of this series, we will look at the interaction of sprinklers and ventilation before moving on to lay out the components of smoke management systems. In the meantime, if you have any questions about this blog, or wish to discuss your own project with one of our fire engineers, please contact us.

Lawrence Webster Forrest has been working with their clients for over 25 years to produce innovative and exciting building projects. If you would like further information on how LWF and fire strategies could assist you, please contact Peter Gyere on 020 8668 8663.

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