Work done and results - L.S.FIRE - Filtering.pdf · 2 days WP2.1.2 technical meeting (end of july 2009) and in presence of technicians from LSFire, LNE and Currenta labs. At the end

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Transport Fire Safety Engineering in the European Union

Transfeu WP2 Subtask 2.1.2 Development of small-scale test method for fire effluents

Step 2: Filtering Plans according to DoW:

The necessity to safeguard the integrity of the sensitive FTIR cell requires the use of a system of filters that remove the particles and remains efficient for the whole duration of the test. LSFIRE, LNE, SP and CUR will study the following parameters: type of material of the filters, porosity, and level of temperature.

Work done and results 1. Forward

According to the plans of Transfeu DoW WP2 subtask 2.1.2 step 2, LSFire, LNE, SP and Currenta have planned and carried out some tests to verify the best configuration of filtering system in FTIR sampling line for removing the smoke particles in order to safeguard the integrity of the sensitive gas cell and so keeping it efficient for the whole duration of test. It was then necessary to proceed to an experimental check for confirming the efficiency of the system during the test period of 20 minutes. In the past a specific type of PVC cable caused the filter block (planar of fibre glass or PeTFE, 1 µm) after two or three minutes of 4 lt.min flux passage. Luckily, at LSFIRE there are still stored some metres of this cable in quantity sufficient for distributing the specimens to all the three laboratories –LSFIRE, LNE and CURRENTA – for repeating the test with the planned filtering system. According to the information supplied by SP (that had tested himself products of this kind, with big production of particles) the cylindrical filter of PTFE or ceramic they were testing in the heated housing –Ø 30 mm / length 75 mm – wouldn’t present blocking problems, considering even the expected flux, that in the final version should be 2 lt./min maximum. In preparation of the meeting of the three laboratories in Controguerra, LSFIRE provided then for realizing the whole system shown in Figure 3, buying the single components which are following listed:

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A

Filter of sintered steel, connected to the heated housing of the primary filter of 2 µm porosity

B

Filter of PTFE of 2 µm, kept at 180 °C

C

Probe heated at 180 °C with interchangeable core

of PTFE

D

Cooler of the sampling flow, after the cell

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E

Peristaltic pump of PTFE

F

Flow meter

The experimental part has been conducted in LSFire laboratory of Controguerra (Italy) during the 2 days WP2.1.2 technical meeting (end of july 2009) and in presence of technicians from LSFire, LNE and Currenta labs. At the end of the test, after having analyzed the data and heard the different suggestions, some further improvements to the apparatus have been decided.

2. Smoke chamber fire model

The smoke chamber fire model (ISO 5659.2) with internal sampling probe according to EN TS 45545.2 annex C method 1 was preliminary used as reference configuration following the main conditions also set for the study of modelling performed by VTT in the step 1 of the same subtask and described in the doc. “Smoke chamber modeling Report - June 2009”. 3. Testing set-up 3.1 Probes for sampling configurations

Other than what is described in EN TS 45545.2 probe which is called “configuration probe 1”, it has performed tests also using a pre-filtering cylinder covering open ended probe which is called “configuration probe 2”. The use of pre-filtering system on the internal probe has choosen in the way to improve the filtering system and reduce the work done by the main filter (outside the chamber). This solution would increase the general efficiency in order to keep the sampling flow as constant as possible and without clogging effects. The two different configurations are described in figure 1 and 2. The pre-filter consists in a sinterized SS cylinder 30mm diameter and 300mm length with a porosity of 2 micron. It is also heated at 70-80 °C by main filter housing heating conduction.

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FIGURE 1

FIGURE 2

To the FTIR gas cell

Main filter

Housing with temperature controller: 180

°C

PTFE cylindrical filtering cartridge

75mm long, diam:30mm Porosity 2 micron

SS internal probe d=4mm

accoirding to EN TS 45545.2

annex C method 1.

Length: 300mm. Open ended

PTFE heated sampling line (180 °C)

Fire effluents

Smoke chamber

Pre-filtering SS unit

300mm long ; 30mm diameter

2 micron porosity

Configuration probe 2

150mm

To the FTIR gas cell

SS internal probe d=4mm

accoirding to EN TS 45545.2

annex C method 1.

Length: 300mm. Open ended

Main filter

Housing with temperature controller: 180

°C

PTFE cylindrical filtering cartridge

75mm long, diam:30mm Porosity 2 micron

PTFE heated sampling line (180 °C)

Fire effluents

Smoke chamber

Configuration probe 1

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3.2 Main filter

The main filtering system was a cylindrical PTFE cartridge of 30mm diameter and 75mm length with a porosity of 2 microns into a heating housing having a temperature controller set to 180 °C. The use of PTFE was previously decided because HF may be reactive with fiber glass and ceramic may absorbe HCl also at high temperature. 3.3 Sampling line

A heated PTFE sampling line was used to join the main filter to FTIR gas cell and the temperature was set to 180°C. 3.4 Gas cell

A FTIR gas cell of 0.75l volume and a pathlenght of 8m was used for fire effluent sampling and in order to increase the level of safeguard of internal mirrors a small circular planar filter (25mm diameter) with a PTFE membrane of 1 micron porosity was placed in the way in of the cell (2nd filter). The gas cell was heated at 180 °C. 3.5 Way out of the cell

The sampling line after the cell consisted in a cooler system to decrease the temperature of sampling flow at less than 30 °C for improving the flow measurement and increase the stability of it before to go in the pump. The pump was then collected to a flow meter which was used to set and check the sampling flow. The complete scheme of sampling line is shown in the figure 3. 3.6 Sampling flow rate The sampling flow rate was set at 1.5 l/min for 3 different technical reasons. The first one is that as the VTT study on modeling demonstrated, no influences in smoke measurement if the gas sampling flow is set between 1 and 2 l/min. The second is concern the response time of the cell which shall be short enough to permit at least 4 readings per minute. It means an interval time between toxicity measurement less or equal to 15s. This condition shall be reached with a gas cell of limited volume between 0.250l and 0.375l which require a flow rate at max of 2 l/min. A third reason is limiting the volume drawn out of the chamber during 20min test period in order to avoid any under-pressure effects inside the smoke chamber. This can be respected only working with a sampling flow rate less than or equal 2 l/min. 4. Test condition and material The choice of product to be tested was linked to the experience of LSFire in cable testing. In a previous internal research of LSFire, a very difficult testing conditions were reached carried out some tests with PVC cables specially because the big amount and type of particles produced by the combustion in smoke chamber caused a totally clogging of main filtering system during the FTIR sampling process in a very short time (5-6 min).

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The reason is to be explained by the use of a main filtering having a planar membrane but the extremely dirty conditions of smoke may be used as a pass-fail test for the new filtering system configuration to be optimized for the new method. By this way, it was thought that a best response in terms to HCl measurements will be given comparing the results obtained perform some tests at two different new probe configurations. A PVC cable was chosen as testing samples. The irradiance level set for testing was 50 kW/m2 no pilot flame.

Figure 3 – Scheme of FTIR sampling

PVC Cable

5. Data collection The collection of data period was 20min. The smoke density values were recorded with a scan interval of 5s and the toxicity data (concentration of toxic gases values) each 15s (spectra interval time). The spectral resolution was set at 4cm-1 and the nr. of scans were 4 per spectrum. 6. Results

Smoke Chamber

Probe/prefilter

Main filter (180°C)

Sampling line (180°C)

2nd

filter

Gas cell

(180 °C)

Cooler (5 °C)

Pump

Flowmeter (1,5 l/min)

FTIR Spectrometer PC

Collection

of spectra

Exhaust

Fire effluents

A

B

C

E

F

D

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The comparison between the smoke density, and detected gases curves is performed and following reported.

6.1 Smoke density The comparison shows a very similar trend between the curves and no differences are substantially identified. Anyway, it can be assumed that the two different configuration of probe do not cause any effect in terms of smoke density measurement because the variation of data is certainly within the repeatability requirements of the ISO 5659.2 standard.

Smoke density (Ds)ISO 5659.2 - 50 kW/m

2 no pilot flame

0

100

200

300

400

500

600

700

800

0 200 400 600 800 1000 1200

Time (s)

Sm

oke d

ensi

ty (D

s)

Configuration probe 2 (with prefilter) Configuration probe 1 (no prefilter)

6.2 CO and CO2 concentration The curves of CO and CO2 shows trends which can be linked to the smoke density plots. So it seems that no appreciable variation in the CO/CO2 detection are directly linked to the different probe configuration (with and without prefilter).

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CO concentrationISO 5659.2 - 50 kW/m

2 no pilot flame

0

500

1000

1500

2000

2500

0 200 400 600 800 1000 1200

Time (s)

Co

nce

ntr

ati

on

(p

pm

)


CO2 concentration

ISO 5659.2 - 50 kW/m2 no pilot flame

0

2

4

6

8

10

0 200 400 600 800 1000 1200

Time (s)

Co

nce

ntr

ati

on

(%

)


6.3 HCl concentration A different evaluation can be done looking to the Hydrogen chloride concentration curves overlapping. It shows without any doubt the effect due to the different probe configurations in terms of delay and amount of gas detection.

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HCl concentrationISO 5659.2 - 50 kW/m

2 no pilot flame

0

1000

2000

3000

4000

5000

6000

0 200 400 600 800 1000 1200

Time (s)

Co

nce

ntr

ati

on

(p

pm

)


It can be explained as the condensation of HCl on the pre filter wall which cause a double simultaneous effect. The first is concern the starting of detection by analyzer because the first data of gas concentration is detected by the gas cell after 30-45s from the beginning of the test; at contrary in the configuration probe 1 (no pre filter) the gas is early detected in the first predictable point (15s from the beginning of the test). The second is concern the general amount of gas really developed during the combustion. The peak of 5389ppm was obtained at 315s during the configuration probe 1 test (no pre filter) and 4082ppm at 1185s in the configuration probe 2 (with pre filter). So, it is clear that for the test using configuration 2 the prediction of HCl is vitiated and strong influenced by the pre-filtering probe and in terms of toxicity risk can hide a very dangerous condition specially in the first stage of fire. The difference between the way to stop the smoke particles are shown in the following pictures. The porosity of the pre-filter and main filter cartridge is the same, so at the end of test, when the pre-filter is used the main filter cartridge was no dirty, while without pre filtering probe all the particles were stopped by the main filter cartridge.

Pre filter and main filter PTFE

cartridge after “configuration probe Main filter PTFE cartridge after

“configuration probe 1” test

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2” test

7. Conclusion The study has pointed out that also in the worst conditions of combustion performed in smoke chamber test in terms of particles emission, the use of a main filtering system having an heating housing of 180°C, a cylindrical cartridge in PTFE of 75mm length / 30mm diameter / 2,0 micron porosity and with a sampling flow of 1,5 l/min, it able to work without any filter clogging problems for at least 20min. This configuration will be take as standard set-up of filtering system for the future work of the sub task WP 2.1.2 and in the contribution of improving the specific part of the new standard method for toxicity measurement to be finalised in Transfeu programme. 8. Additional improvements During the technical group meeting it was decided to add some apparatus to improve the configuration of FTIR sampling/measurement system. A pressure gauge/transmitter will be used for monitoring any variations of pressure in the cell in order to make more precise the measurement of concentration of gases contained in the effluents. It was also decided to adopt, as protection filter, directly before the cell, the filter suggested by Currenta, studying even a suitable system for keeping it at a temperature of 150/180 °C. Currenta will provide for supplying with it both LSFIRE and LNE within the first half of September.

Pressure gauge / transmitter

Filter to be mounted before the cell

Claudio Baiocchi / Silvio Messa (LSFire)

Documents

Work done and results - L.S.FIRE - Filtering.pdf · 2 days WP2.1.2 technical meeting (end of july 2009) and in presence of technicians from LSFire, LNE and Currenta labs. At the end