LARGE – SCALE FIRE TEST WITH A PASSENGER CAR IN AN OPEN AREA

This article briefly presents the results of measurements of the temperature field, the heat flux density field and chemical analyses of sampled smoke for the content of selected toxicants during large-scale fire test carried out with a passenger car in an open area. The measured values are compared with the values calculated from numerical modelling using the FDS computer software. The severity of the problems is documented by selected data from the statistics of fires of cars in the Czech Republic in the period of 2004-2013 and by the devastating effects of fires on their crew and its surroundings.


INTRODUCTION
Car fires represent a serious danger for their crews and for the environment, which can be documented by the statistics of fatalities (F) and injured (I) persons and the direct damage caused by the fires in the Czech Republic and in the world [1], see also chapt.2. Whilst motor vehicles passed the homologation (approval of technical competence in road traffic) as the type and subsequently operate the STK (State Technical Inspection) controls [2], then can start a fire consequently spreading to the whole vehicle i. e. into the interior due to impact in a crash or technical failures or human error.The highest fire load in the vehicle no longer represents only the fuel in the fuel tank, but also a relatively large weight / proportion of combustible plastics, upholstery materials and coatings in construction including electrical wiring insulation that do not pass in the M1 type passenger cars mandatory laboratory tests for flammability, ignitability , the rate of surface flame spread.Nor flammable materials in the type M3 vehicles (buses) are tested for toxicity of combustion products [3].Car parking in the urban area, close to residential buildings, garages and in columns may represent a potential hazard.
The most objective assessment of the fire hazard of the motor vehicle type is a full-scale fire test simulating a fire under defined conditions and connected with measuring the heat release rate, the heat fluxes, the temperature field, the amount of smoke released and the concentration of pollutants contained therein / toxicants incl.rate of spread of fire until a flash-over rise.There is already a number of published results of the tests carried out with the aim of their use in the construction of motor vehicles and the creation/specification of standards and regulations specifying technical vehicles´ parameters and their testing [1] - [6].

STATISTICS OF FIRES OF PASSENGER MOTOR VEHICLES (PMV) IN THE CR
Danger of the PMV´ fires and accidents in the Czech Republic can be documented by the data in Fig. 1 -5.According to the EU data the share of domestic passenger transit increased from 73.8% in the year 2002 to 74.8% in the year 2012 in units pkm (passengerkilometres) [8] In the Czech Republic.

THE DEVASTING EFFECTS OF FIRES ON THE VEHICLE´S OCCUPANTS AND SURROUNDINGS
Potential disruptive effects of PMV´ fires on their crew and surrounding area can be divided into the following factors a/ to f /:

a / intoxication by fire effluents
The harmful health effects of substances occurring in fire effluents are characterized in the Tab. 1. [10] Explanations: PEL = Permissible Exposure Limit, STEL = Short Term Exposure Limit

c / visibility loss after smoke´s filling the interior of vehicle cabin
The visibility in smoke is expressed in meters (m), the smoke extinction coefficient (optical density per meter) in (m -1 ).
The smoke opacity (O) means the rate of extinction of the light beam passed through a layer of smoke.
The optical density of the smoke (D) means a common logarithm of opacity.
In a smoke-filled space with D = 0.5 the rate of escape decreases to about 0.3 m/s.

d/ suffocation due to lack of the oxygen in the affected cabin
Potential devastating effects in terms of lower oxygen content in the air are illustrated in Tab. 3. [11] [O2 ](% v/v) Effect

FIRE TEST
FT was implemented in the passenger car as a sample non-approved vehicle -teaching aid (hereafter it is referred to as "car") with dimensions as shown in Fig. 6 with technical specifications mentioned below.The scene of the fire was located in the vicinity of the UCEEB campus with two L-shaped screens to protect from the prevailing SW wind and away from a local road and the closest buildings, see Fig. 5.The automobile was placed in a catch basin to prevent fuel penetration into reinforced ground using a crane on 3 pillars (steel pipes) with bilateral end plates; pillars were interconnected with steel angles.
The fire of the automobile was simulated by a fuel leakage from the fuel tank and ignition of vapours from the exhaust under the car as follows: -15 l spilled AP fuel (Automobile petrol) was placed in an iron tray (90 x 90 x 15) cm under the vehicle before the rear wheels, -AP in the tray was ignited with a flaming torch by a fireman in the protective clothing.
The UCEEB meteo -station measured before and during the test: -temperature at heights of 5 cm (grey triangular points) and 2 m (blue plus points) above the ground and humidity of air (blue connector) with positions relative to the scene of the fire according to Fig. 7 and with the results in the Fig. 8, -wind speed and direction near the fire place with the results in the Fig. 9.

Fig. 7. Sketch map showing positions of the Weather Station and the PMV during the fire test [1]
Weather Station, Fire place -location of the test, the Main UCEEB building, UCEEB technical background (single), wind screen, poles for mounting devices and gauges Fig. 8. Graph of temperature and humidity in the air during FT [1] Fig. 9. Graph of the progress of the wind speed and its direction during FT [1] The results of the wind speed measuring during the test with the anemometer EVA 935 -TH5 in the position of about 1 m from the inside corner of the L-leeward wall toward the car and at a height of approximately 1.5 m above the ground: v = <0.01 to 1.00> m / s.

Measuring the temperature field and the irradiance
The temperature field was measured inside and outside the car interior during the fire test, the irradiance outside the car only, in both cases at defined positions (x, y, z).
The temperature was measured in 20 positions outside the vehicle and the irradiance in the following four positions according to the Fig. 10.Temperatures (° C) were read using the K type thermocouples (TCs) in the positions indicated by symbols T1 to T20, from which: --8 items were at the height of 2 m (positions T1 to T8) --8 items were at the height of 3 m (T11 to T18 positions) --4 items were placed directly above the automobile Thermocouples (TCs) were fixed with their hot ends on cords stretched between the towers in the desired positions.By means of compensating cables they have been connected with the PC and the logger that were placed behind the screen.Irradiances in kW/m2 were scanned with 4 radiometers of the type SBG 01-100 Heat Flux Sensor in positions R1 to R4 and at heights of 1.5 m, see Fig. 10.The bodies of radiometers (inlets and outlets of cooling water, electricity conductors) were placed on iron racks and directed with measuring dots to the car.Data radiometers lines were pulled behind a screen to the logger ALMEMO 5690-2 and PC.

Fig. 10. The perspective view of the positions of thermocouples (T1 -T20) and radiometers (R1 -R4) and their coordinates (x, y, z) outside the test vehicle during FT. [1]
Graphs are developed from the results of temperature and flux density measurements during the time assay [1].For this article the maximum measured values are evaluated and listed in the following Tab. 4 and 5 with the estimation of their expanded uncertainty U (k = 2) = ± 1.8°C Tab. 4. The maximum measured temperature values Tmax outside the burning automobile with the times τ of their achievement [1] Sensor   The beginning of the coordinates x = 0, y = 0, z = 0 is at the intersection of the perpendicular from the geometrical centre of the automobile to the ground.
Tab. 6.The maximum measured temperature values Tmax on thermocouples (TCs) inside a burning automobile with times of their achievement τTmax [

Sampling and chemical analysis of samples taken for the content of pollutants inside the burning automobile
The fire effluents in the automobile interior were sampled using the metal probes No. 1 and No. 2 inserted through a small window of the right rear door.Compensating lines from the CO detectors were kept in a protective tube through a small window of the left rear door.
Both tubes 1 and 2 rattled in front of the rear right seat headrest.At their opposite end, at the distance of about 2 meters from the automobile, there was attached silicone tubing, about 10 m long, kept behind a protective wall and here at the measuring station they were connected: through filters and a refrigeration unit to the analyser Testo 350 L (1) with sensors measuring CO, CO2, O2, NO, NO2, SO2, through the mass flowmeter GFM17 / Air (Aalborg), the needle valve, the variable-area flowmeter to sampling Supelco -ORBO tubes (2).Data collection includes the notebook with the SW "Testo Emission Easy v. 2.0".
Graphs are also prepared from the measurement results of the CO, CO2, O2, NO, NO2 and SO2 gases concentrations during the test [1].The maximum measured values are evaluated for this article, see Tab. 7 with the estimation of their expanded uncertainty U can be seen in Tab. 8.

Measurement of the burning automobile weight loss to computational estimation of the heat release rate (HRR)
For the weighing need of a automobile weight loss during a fire test due to burning off flammable materials in a vehicle design CTI -CF developed and installed fireproof scales with this technical specifications: -Weighing in 3 points -stands resting on three strain gauges (hereinafter referred to as SG) Ø = 150 mm and v = 35 mm, max.weighing capacity = 20 kN (2,000 kg) and a resolution of 100 g, -SG data cables were connected with the data logger located at the right corner of the protective screen, -SG and data cables protection from high temperatures: tiling with a mineral insulation.Weighing began at 2:14:53 p.m and was finished with the still functional scales in 702.7 seconds with a final weight loss of 1.79 kN, ie.179.67 kg.Acceleration in weight loss was observed after a period of about 400 s.About 111,87 kg other combustible materials in the construction and inside the vehicle burned after deducting the known quantity of the diesel fuel (DF) in the tank (about 32.8 kg) and 5 pieces of tires (about 35 kg).Information about these kinds of flammable materials, their quantity and FTCh however, failed to get from the vehicle manufacturer, therefore the calculation of HRR and the total amount of heat released was not implemented.The expanded uncertainty U (k = 2) of the measured data with weighing is estimated in the Tab.10.Set of all sensors 10 kN 0,199 0,104 0,059 0,073 S. Komárníková estimated the total amount of released heat in her dissertation [10] on the basis of the estimation of flammable materials sorts and their quantities in the tested automobile.

PHOTO RECORDS OF THE FIRE TEST (FT) COURSE
The course of the automobile fire was captured by two video cameras and thermocameras placed against the forehead and right side of the vehicle.Records were evaluated in a table with the following data: real-time, time from ignition, event description, and the corresponding video and thermo records.Tab.11.Evaluation of major phenomena surrounding the automobile fire during a FT [1] Real time

Time from ignition
Event description

A COMPUTER SIMULATION OF THE FT USING SW FDS
The FT was numerically simulated by computer using the SW FDS 6.1.1/Pyrosim2014.2.0807 with the graphical output using Smokeview January 6.1.11SW with generating the automobile geometry and basic computing network, see Tab. 12.The total modelling time was 2100 seconds, the same as the real fire test lasted.
Tab. 12: Parameters of the numerical network [1] Network title The chemical reaction of burning was applicated as a source of combustion for the combustion calculation using the data from Tab. 13.This model was selected in order to be possible to computational predicting the field concentrations of the CO, O2 and CO2 gases in time and space.The concentration of toxicants was estimated according to the chemical reaction of the PUR foam combustion in the seat upholstery.The initial and boundary conditions, the flow model, the simulation model, the radiation model and the simulation length were set to correspond as closely as possible the conditions during the test fire.Calculations of temperatures, irradiances and concentrations of selected toxicants inside the automobile 10 were carried out at measuring points according to the Fig. 10 and 11.

Xmin-Xmax
Tab. 13.Material characteristics -Input data for the FDS [ The result of modelling [1] is processed in: a/ graphs of the time histories calculated values of: temperature T (°C) -irradiance q (kW/m 2 ) -and CO, O2, NO, NO2 and SO2 concentrations (mol/mol) b/ tablets, see Tab. 14 -16 c/ comparing records of thermo-camera and visual model sections of temperature fields during a fire in the 30th, 60th, 120th, 240th and 360th s, see 2nd Annex.

b/ heat and open flames and hot smoke effects
1]