STEFAN SVENSSON Fire ventilation Stefan has a PhD in Fire Safety Engineering and he is an Associate Professor in Fire Safety Engineering. He has for many years worked as a teacher at MSB Revinge but has also been employed at Lund University and for many years worked as a part-time firefighter/ crew commander. He has authored numerous books, reports and articles, and conducts an extensive devel­ opment work for the national as well as international fire service community. Fire ventilation © Swedish Civil Contingencies Agency (MSB) Cover photo: Åsa Brorsson Text: Stefan Svensson Editor: Kristina Malmstedt-Svensson Printing: DanagårdLiTHO Layout: Advant Order Nr.: MSB1565 – May 2020 ISBN: 978-91-7927-036-0 Swedish edition: MSB1477 – februari 2020 Table of content Fire ventilation – introduction _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 9 Objective and purpose of fire ventilation _ _ _ _ _ _ _ _ 10 Openings and fire ventilation _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 11 Venting a room exposed to fire _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 13 Venting of rooms adjacent to a fire room _ _ _ _ _ _ _ _ _ _ _ _ _ 13 Create openings to gain access to a fire that has spread into the structure (a structural fire) _ _ _ _ _ _ _ _ _ _ 14 Venting for mop-up, salvage and overhaul _ _ _ _ _ _ _ _ _ _ _ _ 15 Different ways of venting fire gases _ _ _ _ _ _ _ _ _ _ _ _ 15 Horizontal fire ventilation _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 16 Vertical fire ventilation _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 16 Mechanical fire ventilation _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 16 Fundamental principles _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 17 Fuel control or ventilation control _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 18 Venting the space exposed to fire or venting adjacent spaces _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 20 Suppression first or venting first _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 21 Fire behavior _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 23 The four phases of a room fire _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 23 The initial stage _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 24 Flashover _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 24 The fully developed fire _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 25 The cooling phase _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 28 Fires involving several rooms, larger rooms or most parts of a building _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 28 From fuel control to ventilation control _ _ _ _ _ _ _ _ _ _ 29 Fire gases _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 33 Fire gases consist of air and combustion products _ _ _ 33 Properties of fire gases _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 34 Transparency of fire gases _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 34 Flammability of fire gases _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 35 Toxicity of fire gases _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 36 Reactivity of fire gases _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 38 Hot fire gases _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 39 The spread of fire gases _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 41 The flow and spread of fire gases _ _ _ _ _ _ _ _ _ _ _ _ _ 41 Thermal buoyancy _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 44 Thermal expansion _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 46 Production of combustion products _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 48 Temperature differences between indoor and outdoor air _ _ _ _ _ 49 External wind conditions _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 54 Ventilation systems for comfort _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 59 Spread of fire gases in practice – a holistic view _ _ _ _ _ 62 Working with fire ventilation _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 71 Size of openings _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 71 Exhaust openings _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 74 Inlet openings _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 77 Horizontal fire ventilation of fire-exposed spaces _ _ _ _ 83 Vertical fire ventilation of fire-exposed spaces _ _ _ _ _ _ 84 Fire ventilation of spaces adjacent to the fire room _ _ _ 85 Mechanical ventilation using fans _ _ _ _ _ _ _ _ _ _ _ _ _ 86 Negative pressure ventilation _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 88 Pressurization of adjoining rooms _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 92 Positive pressure ventilation _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 94 Smoke curtains _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 106 Hydraulic ventilation _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 109 Structural fires and fire ventilation _ _ _ _ _ _ _ _ _ _ _ 111 Structural fires – fires in hidden spaces _ _ _ _ _ _ _ _ _ 111 External structural fires _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 113 Internal structural fires _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 113 The spread of fire and fire gases during structural fires _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 114 Fire ventilation of larger cavities _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 115 Fire ventilation of smaller cavities _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 116 Creating openings in structural elements are hazardous but often necessary _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 117 Methods for creating openings for accessing structural fires _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 118 Tools for creating openings _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 120 Electric power tools _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 120 Combustion engine powered tools _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 120 Examples of various tools and their basic functions _ _ _ _ _ _ _ _ 121 Special tools _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 123 Safety when working at heights _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 125 Fall protection _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 125 Working at heights _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 130 Safety when working from a ground ladder and a ladder platform vehicle _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 131 Safety when working without a ladder platform vehicle _ _ _ _ _ 132 Examples of various structures _ _ _ _ _ _ _ _ _ _ _ _ _ 135 Exterior walls _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 139 Interior walls _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 142 Sheet metal roofing on older buildings _ _ _ _ _ _ _ _ 143 Tiled roofs _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 145 Roofs with tarred roofing felt/waterproof paper roof 146 Roofs with corrugated metal sheeting _ _ _ _ _ _ _ _ _ 147 Fixed installations for fire ventilation _ _ _ _ _ _ _ _ _ _ 149 Tactics _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 157 Using resources effectively _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 157 Coordinated measures _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 158 Gaining and maintaining control _ _ _ _ _ _ _ _ _ _ _ _ 160 Tactical patterns during fire ventilation _ _ _ _ _ _ _ _ 160 Examples of firefighting situations _ _ _ _ _ _ _ _ _ _ _ 163 Small fire in relation to the size of the room _ _ _ _ _ _ 164 The initial stages of the fire _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 166 The fully developed fire _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 169 Ventilation controlled fire _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 171 Staircase with hot fire gases _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 173 Staircases with cold fire gases _ _ _ _ _ _ _ _ _ _ _ _ _ 174 Basement fires _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 176 Structural fires _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 178 Some final words _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 183 Further reading _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 184 Illustrations and photos _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 189 Preface to the revised edition This book was first published in 2000 and was already back then based on research as well as experience.