Annual Fire Safety Engineering Conference 2013 Dr. Björn
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Annual Fire Safety Engineering Conference 2013 A DECADE OF SCANDINAVIAN RESEARCH AIMED AT BENEFITING THE FIRE SERVICE Dr. Björn Karlsson Arnheim, 12-13 November 2013 Dr. Björn Karlsson 1 CV, Dr. Björn Karlsson • B.Sc. Civ Eng, Heriot-Watt University, Edinburgh, 1985 • Ph.D. in Fire Safety and Risk Engineering, Lund University, Sweden, 1992 • Associate Professor at Lund University, 1992-2001 • Associate Professor, Civ. Eng. Dept., University of Iceland, 2006- • Director General of the Iceland Fire Authority 2001- 2010 • Director General of the Iceland Construction Authority • In charge of Fire safety, Electrical safety and Building Regulations, also control the Fire Service College Dr. Björn Karlsson 2 Contents • Background • Flashover, backdraft, smoke gas explosion • Ventilation • Suppression • Tactics • Conclusions Dr. Björn Karlsson 3 Background • Fire fighter training and experience is important, but buildings are getting much more complex (atria, underground, etc) • Rapid progress in understanding fire phenomena, computer programs, etc • Important to use new technology in training • Here: Give overview of research for fire service, researchers from Lund University who subsequently worked in fire service Dr. Björn Karlsson 4 Flashover, backdraft, smoke gas explosion • Very hazardous phenomena • Controversy over terms used – Flameover, rollover, lean and rich flashover, etc • Research project with aims to – Clarify terminology – Increase understanding of the dominant thermal and chemical processes – Produce basis for teaching material Dr. Björn Karlsson 5 Flashover, backdraft, smoke gas explosion Temp Flashover Growht to flashover Backdraft Tid Dr. Björn Karlsson 6 Motivation for training Fire Fighters • Fire fighters face dangerous situations – Must understand the chemical and physical processes involved – Must understand the warning signs – Must know how to deal with these problems • A compartment fire can develop in many different ways, not all are hazardous Dr. Björn Karlsson 7 Fire development in well ventilated spaces • Well ventilated fire without spread to other item – A very common situation – Easy to deal with • Well ventilated fires leading to Flashover – Occurs in about 5-10% of all building fires – The warning signs are important Dr. Björn Karlsson 8 Flashover, “A sudden event” Extinguishment 1000 900 800 Temp 7 700 Temp 8 ) 600 Flashover C Temp 9 ° ( 500 Temp 10 T 400 300 Temp 11 200 Temp 12 100 0 0 200 400 600 800 Time (s) Dr. Björn Karlsson 9 Warning signs of a potential flashover • Increasing speed of the gases leaving the room • Neutral layer moves towards the floor • The colour of the smoke? – Very much depending on the material burning Dr. Björn Karlsson 10 Fire development in poorly ventilated spaces Temp Fully developed fire Flashover B Lack of oxygen A Time Dr. Björn Karlsson 11 Fire development in poorly ventilated spaces • Four common Temp Fully developed fire outcomes: – Self-extinction Flashover B – Auto-ignition of gases Lack of oxygen – Flashover A – Backdraft Time Dr. Björn Karlsson 12 Self-extinction • Very common • Easy to deal with • Can still create dangerous conditions for the people inside the building Dr. Björn Karlsson 13 Auto ignition of the gases Temp Auto ignition Flashover Growth to flashover Lack of oxygen Tid Dr. Björn Karlsson 14 Growth to Flashover Temp Flashover Growht to flashover Backdraft Tid Dr. Björn Karlsson 15 Backdraft • The most hazardous situation • Conditions favourable for backdraft are – Well isolated room – Fuel is placed in the upper part – A smouldering fire that has been ongoing for a long time Dr. Björn Karlsson 16 Occurrence and mitigation of backdraft • Frequency – How often does the phenomena occur? • Warning signs of a potential backdraft – The colour of the smoke? • A new method for mitigating backdraft – The cutting extinguisher Dr. Björn Karlsson 17 Warning signs of a potential backdraft • The fire may be pulsating • No visible flame in the fire room • Whistling sounds around doors and windows • If the fire has been burning for a long time in a concealed space, a lot of unburned gases may have accumulated • Hot doors and windows Dr. Björn Karlsson 18 Smoke gas explosion • Definition – When smoke gases are transported into an enclosure adjacent to the fire compartment, these can mix well with fresh air. This mixture can spread through parts of, or the entire volume of the enclosure and its concentration be within the flammability limits of the mixture. If the mixture ignites the increase in pressure may be extremely high. This is called a smoke gas explosion Dr. Björn Karlsson 19 Warning signs of a potential smoke gas explosion? • Is the construction well sealed? • Does the building construction contain hidden spaces? • Are the building elements themselves combustible? • Are there any unsealed penetrations leading from the fire compartment, such as ventilation ducts? Dr. Björn Karlsson 20 The Grey Zone Fire Development Temp The grey zone Flashover Growth to flashover Backdraught Time Dr. Björn Karlsson 21 Results • The phenomena Flashover, Backdraft and Smoke gas explosion occur relatively seldom but can involve great danger to fire fighters • The work divides potentially hazardous situations into categories based on fundamental physical and chemical processes • These categories are observed in practice and experiments have been performed for verification • The phenomena are closely related and it can in some cases be difficult to distinguish one from the other Dr. Björn Karlsson 22 Result A new textbook for Fire Fighters And Fire Officers used by the Swedish Fire and Rescue Training Facilities Dr. Björn Karlsson 23 Backdraft • Backdraft arises from an under-ventilated fire • A majority of fires are under-ventilated, or limited to first item ignited, when the fire service arrives on the scene • Most fire research work over the last 40 years has concentrated on well-ventilated fires • In under-ventilated fires one must deal with both thermal and chemical processes • Our aim: Educational material for fire fighters Dr. Björn Karlsson 24 Dr. Björn Karlsson 25 Dr. Björn Karlsson 26 Experimental apparatus: Backdraft Dr. Björn Karlsson 27 Salt water modelling Dr. Björn Karlsson 28 Dr. Björn Karlsson 29 Risk of Backdraft vs Tactics Dr. Björn Karlsson 30 Risk of Backdraft vs Tactics Four situations studied 1. Offensive attack, BA team enters front door 2. Defensive attack, natural ventilation by opening a window at the back 3. PPV at high flow rate 5.38 m3/s. 4. Incorrect use of PPV at 5.38 m3/s, but closed outlet window at the back Dr. Björn Karlsson 31 Risk of Backdraft vs Tactics Dr. Björn Karlsson 32 1. Offensive attack • People left inside the compartment • Time is a critical factor • BA team will enter through the front door and cool the hot gases 1. Offensive attack Gravity current speed : 1-2 m/s, a flammable region is created in only a few seconds 2. Defensive attack, natural ventilation • Compartment evacuated • Time not as critical as in Scenario 1 • No unnecessary risks are taken • There are enough resources to perform the ventilation 2. Defensive attack, natural ventilation Dangerous conditions are reached fast, the compartment is more quickly vented, demands resources, protecting facade 3. Offensive attack, PPV • Using PPV at an early stage of an operation is getting more common • Sometimes used in life-saving operations • Recommendation: ”Use with great caution” • Resources needed at discharge opening 3. Offensive attack, PPV Effective way of clearing the compartment of fire gases, increased mixing for a very short period, discharge opening must be protected with water 4. Incorrect use of PPV •What happens if the discharge opening is blocked ? •Scenario 4 simulated without the discharge opening 4. Incorrect use of PPV Explosive mixture collects more at ceiling level, smoke can be forced, due to the overpressure, into areas not yet damaged by the smoke Contents • Background • Flashover, backdraft, smoke gas explosion • Ventilation • Suppression • Tactics • Conclusions Dr. Björn Karlsson 41 Ventilation 1. Experimental Study of Fire Ventilation Actions During Firefighting Operations 2. Experimental Study of Fire Ventilation Procedures in a Large Hall 3. Investigating positive pressure ventilation (see Presentation A-2) Dr. Björn Karlsson 42 1. Study of fire ventilation during fire fighting operations • Purpose of the tests – investigate the effect of measures taken by fire & rescue services, including positive pressure ventilation – to provide fire & rescue services with qualitative data to be used as a basis for decision making on the fire ground – 15 experiments • Experimental set-up – fire fighter training facility (concrete/lightweight concrete) – 0.50 m diameter heptane pool, burn time app. 700 seconds, RHR appr. 0.37 MW – PPV by a Typhoon 18T5 fan, nominal flow of 2.7 m3/s Dr. Björn Karlsson 43 The test facility Dr. Björn Karlsson 44 Experimental lay-out Dr. Björn Karlsson 45 Fire fighting scenarios A. via staircase (access route through D4, Room 4, D3), window (W) closed B. via window (W), door between staircase (Room 4) and apartment closed (D3) C. via staircase (access route through D4, Room 4, D3), window (W) open D. via staircase (access route through D4, Room 4, D3), window (W) open, PPV, fan positioned in Room 4 E. via staircase (access route through D4, Room 4, D3), window (W) open, PPV, fan positioned outside door to staircase (D4) Dr. Björn Karlsson 46 2. Study of fire ventilation procedures in a large hall • Purpose of the tests