Fire statistics: an overview

Transcription

1 Fire statistics: an overview Dr. Jeremy Fraser-Mitchell Senior Consultant, Fire Safety BRE Fire Conference, 18 th September 2018 Part of the BRE Trust

2 Availability of Fire Statistics

3 Public domain: Statistical Bulletin

4 Public domain : Statistical Bulletin

5 More detailed analysis in public domain

6 More detailed analysis in public domain

7 Public domain: spreadsheet tables

8 Public domain: spreadsheet tables

9 Public domain: spreadsheet tables

10 Public domain: spreadsheet tables

11 Incident Recording System (IRS)

12 Incident Recording System 125 questions in all

13 IRS incident-level data in public domain In a recent development (August 2018), the Home Office has published a number of data tables containing incident-level data They can be found here:

14 Current incident-level datasets Casualties in fires dataset (ODS, 2.6MB) Daily incidents dataset (ODS, 22.2MB) Domestic appliance fires dataset (ODS, 5.49MB) Dwelling fires dataset (ODS, 35.9MB) Fire-related fatalities dataset (ODS, 99.5KB) Fire stations dataset (ODS, 113KB) Low level geography dataset (ODS, 28.8MB) Non-fire incidents: animal assistance dataset (ODS, 1.67MB) Non-fire incidents: bariatric assistance dataset (ODS, 201KB) Other building fires dataset (ODS, 18.4MB) Road vehicle fires dataset (ODS, 16.9MB)

15 An Application of Fire Statistics

16 The issue: fire spread from external vehicle fires Concern over potential for fire spread (by radiant heat transfer) From: burning vehicle(s) To: combustible material close to the side of the road separation

17 The issue: fire spread from external vehicle fires Concern over potential for fire spread (by radiant heat transfer) From: burning vehicle(s) To: combustible material close to the side of the road separation

18 The issue: fire spread from external vehicle fires Concern over potential for fire spread (by radiant heat transfer) From: burning vehicle(s) To: combustible material close to the side of the road separation

19 The issue: fire spread from external vehicle fires Concern over potential for fire spread (by radiant heat transfer) From: burning vehicle(s) To: combustible material close to the side of the road heat radiation separation

20 The issue: fire spread from external vehicle fires Concern over potential for fire spread (by radiant heat transfer) From: burning vehicle(s) To: combustible material close to the side of the road heat radiation separation

21 How can we estimate the risk of fire spread? Risk = Frequency x Consequence Concentrate on the fire frequency: How often do vehicle fires occur? How quickly do the FRS attend (t FRS )? How large is the vehicle fire? How quickly will the combustible material at road side ignite (t ign )? Consequence: IF (t ign < t FRS ) THEN (fire spreads)

22 Estimating fire frequency (transport statistics) Data from trunk roads in 4 different regions (A, B, C, D) Data collection period different in each region Work out the average interval between fires in each region Estimate number of fires per year

23 Fire frequency data (transport statistics) Region Average interval Std. Devn. interval Region A 103 days 104 days Region B 13 days 13 days Regions C & D 18 days 9 days Region Interval Fires per year Region A 103 days 3.5 Region B 13 days 28.9 Regions C & D 18 days 19.8 Overall (A-D) 52.2

24 Fires involving different types of vehicles (transport statistics) If the numbers of fires of different vehicle types are weighted by the frequency of fires in the different regions, the overall proportion of fires involving different vehicles can be estimated Vehicle type Region A 3.5 fire/yr Region B 28.9 fire/yr Regions C&D 19.8 fire/yr All regions 52.2 fire/yr Motorcycle (4%) Car (19%) Bus (7%) Van (8%) HGV (33%) Tanker (4%) Not specified (26%)

25 National (UK) fire statistics on vehicle fires (FDR1 data) It was necessary to go back as far as 1998 (FDR1 data) to find data that contains details on: the type of road (if applicable) where the fire occurred, and the area of fire damage The former is necessary to eliminate the many vehicle fires that do not occur on a road (e.g. in a garage or car park). The latter is useful because not all vehicle fires will grow to involve the entire vehicle, which is important in assessing the likely ignition of the target material from radiant heat. Heat release rate of fire = 0.5 ~ 1.0 MW/m 2

26 Comparing data from different sources Vehicle type Regions A-D ( ) FDR1 data (1998) Car 9.8 (19%) (62%) Bus / coach 3.8 (7%) 8.1 (5%) Van 4.0 (8%) 19.3 (12%) HGV / lorry 17.2 (33%) 35.3 (21%) Unspecified 13.5 (26%) -(0%) Total no. fires 52.2 (100%) (100%) Subset: crashes 5.8 (10%) 11.0 (7%) Note: FDR1 data limited to: Accidental fires Engine running Motorways and dual carriageways Same geographical areas as Regions A - D

27 Estimate of heat release rate from vehicle fires Vehicle type HRR = 0.5 MW/m 2 HRR = 1.0 MW/m 2 Motorcycle 0.64 MW 1.27 MW Car 1.36 MW 2.71 MW Van 1.56 MW 3.12 MW Bus 1.56 MW 3.12 MW HGV 1.42 MW 2.84 MW Tanker 1.46 MW 2.92 MW FDR1 data (1998), all UK, accidental fires with engine running HRR estimated from area of fire damage

28 Probability distribution of fire size Note: FDR1 data limited to: Accidental fires Engine running Motorways and dual carriageways Same geographical areas as Regions A - D

29 Probability distribution of FRS arrival times Note: FDR1 data limited to: Accidental fires Engine running Motorways and dual carriageways Same geographical areas as Regions A - D

30 FRS arrival times and fire area Note: FDR1 data limited to: Accidental fires Engine running Motorways and dual carriageways Same geographical areas as Regions A - D

31 Radiation from cylindrical flame Conservative approximation: cylindrical rather than conical flame Has an analytical solution readily available (SFPE Handbook) By symmetry, peak radiation intensity on target is a height h above flame base R 2r 2h heat radiation separation

32 Radiation heat transfer Flame geometry (h, r) depends on HRR (which is a random variable) Distance R to target = barrier separation distance + random component U(0,2) F d1-2 is the configuration factor when da 1 is the emitter; we want da 1 to be the target so must calculate F 2-d1 (using reciprocity relationship F 2-d1 /da 1 = F d1-2 /A 2 ) A 2 is only half (either top or bottom) of the total flame Radiant intensity at da 1 = 2 x 0.35 x HRR x F 2-d1 /da 1

33 Time to ignition t ign = k.ρ.c (T ign T air ) 2 / (q ) 2 t ign = time to ignition (s) k = thermal conductivity ρ = density c = specific heat capacity T ign = autoignition temperature ( o C, random variable U(200, 500)) T air = air temperature q = radiant intensity (random variable, function of HRR and separation distance) Will ignition occur before the FRS arrive?

34 Probability of fire spread to combustible material at road side Probability of fire spread as a function of barrier separation distance from combustible material

35 Example Conclusions: Assessing the risk Assuming probability of fire proportional to total no. of vehicles x distance driven Estimate 3 ~ 10 fire per 10 8 vehicle.km Example: AADT = 10,000 vehicles / day A 1 km stretch of road would have (3 ~ 10) x 10-8 x 365 x 10,000 fires / year That s roughly 0.1 ~ 0.3 vehicle fires / year. If a fraction f spreads to the combustible material, that s 0.1f ~ 0.3f spreading fires / year Depending on what number of fires is acceptable risk, determine the separation distance.

36 Summary We can use Fire Stats data in a very wide range of different applications Often the analysis of the statistics is one component (but a vital one) of a wider project Clients are Government and Industry Some statistics are in the public domain We rely on the Home Office for provision of data from the UK (England) IRS databases when more detail is required