The LWF Blog

Fire Engineering Design and Risk Assessment – Fire and Smoke Ventilation – Part 11

March 30, 2017 2:22 pm

In this Fire Engineering Design and Risk Assessment blog series for Architects and others in the business of building design, we have been recently talking about types of fire and smoke ventilation, the relevant legislation and how they fit into a fire protection plan. In this blog, we will look at the use of natural ventilation systems in residential buildings.

 

It is recommended by Approved Document B in England and Wales and the Scottish Regulations Part E, that ventilation be provided from lobbies and corridors through a vent to the outside on every floor, or where the travel distances in the corridor are within 7.5m, from a natural smoke shaft. It should be noted that alternative, mechanical solutions are also available.

 

In those cases where a vent can be provided directly to the outside, the free area of the vent should be 1.5m2, with the top of the vent being no lower than the top of the stairs door from the corridor.

 

The relevant document in Northern Ireland – Technical Booklet E – does not currently give details or recommendations in this area.

 

In those situations where a smoke shaft is used, certain construction tenets should be followed:

 

– The vent between the corridor and the smoke shaft should be a minimum of 1m2 free area, with the free area of the shaft being no less than this at any point.

 

– The shaft’s cross-sectioned area should be 1.5m2.

 

– The dimension of the shaft should be a minimum of 0.85m.

 

– The upper end of the shaft should extend beyond the roof (and any surrounding structures within 2m) by at least 500mm.

 

– The upper end of the shaft should also extend by at least 2.5m above the ceiling height of the highest floor which is served by the smoke shaft.

 

– The vent placed at the head of the stairs should open automatically when the vent operates, upon activation of corridor smoke detector.

 

– The smoke shaft itself should be vertical with a horizontal offset of no more than 4m at a maximum angle of 30 degrees.

 

In situations where the corridor has a single direction of escape, the vent should open automatically on the floor of fire origin (and at the top of the smoke shaft and the vent in the stairway too, where appropriate).

 

In cases where a sterile lobby is to be used, it should be vented rather than the corridors which access the residential units. This allows the 7.5m travel distance to be measured to the lobby door rather than the stair door.

 

In part 12 of this series, we will look at the use of firefighting shafts. 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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