---

The flow shall be measured by a bidirectional probe located at the centre line of the duct and at a minimum distance from the beginning of the straight section of exhaust duct of 8 xD. The length of the straight section of duct beyond the probe shall be at least 4x£>. The probe which is shown in Figure 4 consists of a stainless steel cylinder, 32 mm long and with an outer diameter of 16 mm. The cylinder is divided into two equal chambers. The pressure difference between the two chambers shall be measured by a pressure transducer. The plot of the probe response versus the Reynolds number is shown in Figure 5 (see also Annex C).

The pressure transducer shall have a measuring precision better than ± 5 Pa. A suitable range of measurement is 0 Pa to 200 Pa (when using duct diameters between 250 mm and 400 mm).

The two connection pipes between the bidirectional probe and the pressure transducer shall be of the same length.

Gas temperature in the immediate vicinity of the probe shall be measured by a sheathed К type thermocouple with a maximum diameter of 1,5 mm in accordance with EN 60584-1. The thermocouple shall be positioned so that it does not disturb the flow pattern around the bidirectional probe.

NOTE If more than one thermocouple is used then all thermocouples shall be of the same size and type.

The sampling probe shall be located where the exhaust duct flow is well mixed. The probe shall have a cylindrical form so that disturbance of flow is minimised. The gas samples shall be taken along the whole diameter of the exhaust duct. Examples of suitable sampling probes are shown in Figure 6. The intake of the sampling probe shall be turned downstream in order to avoid soot clogging in the probe. The sampling probe shall be connected to the gas analysers for oxygen (O₂) and carbon dioxide (CO₂) by a suitable sampling line.

The sampling line shall be manufactured from corrosion resistant material, e g. PTFE. The combustion gases shall be filtered with inert filters to the degree of particle concentration required by the gas analysis equipment. The filtering procedure shall be carried out in more than one step. The system shall be capable of removing water vapour.

The combustion gas shall be transported by a pump which does not emit oil, grease or similar products, as these may contaminate the gas mixture.

NOTE A membrane pump is suitable.

A pump capacity between 10 l/min and 50 l/min is recommended. The pump shall generate a pressure differential of at least 10 kPa to reduce the risk of clogging of the filters by smoke.

The sampling line (see Figure 7) shall be connected at its end to O₂ and CO₂ analysers.

At the end of the exhaust duct, an extracting ventilator shall be installed. A minimum exhaust capacity of 1,5 m³/s at normal pressure and at a temperature of 25 °С is recommended.

NOTE Legal requirements may make it necessary for equipment for collecting and washing the effluent to be fitted to the test chamber. This equipment shall be such as to collect all the effluents without causing a change in the air flow rate through the test chamber.

The optical density of the smoke can be measured by two different measuring techniques as described in 4.7.2 and 4.7.3. Although the measurement principle differs for both systems, it has been shown that the two different systems do not give substantially different results [3].

A general arrangement of an optical system is shown in Figure 8.

NOTE 1 Other systems may be used provided that their equivalence to those specified has been demonstrated.

NOTE 2 Based upon experience, white light systems are recommended.

The smoke production measuring equipment shall be located where the exhaust duct flow is well mixed.

A light attenuation system, of the white light type, mounted with a flexible connection to the side ducts of the exhaust duct, shall consist of the following.

1. A lamp, of the incandescent filament type operating at a colour temperature of (2 900 ± 100) K. The lamp shall be supplied with stabilized direct current, stable within 0,5 % (including temperature, short-term and long-term stability).

2. A lens system, to align the light to a parallel beam and with a diameter of at least 20 mm. The photocell aperture shall be placed at the focus of the lens in front of it and it shall have a diameter, d, chosen with regard to the focal length of the lens, f, so that d/f is less than 0,04.

3. A detector, with a spectrally distributed responsivity agreeing with the CIE V(A) function (CIE photopic curves) to an accuracy of within + 5 %. The detector output shall, over an output range of at least two decades, be linear within 3 % of the measured transmission value or 1 % of the absolute transmission.

Calibration of the light attenuation system shall be carried out according to E.4. The 90 % response time of the system shall be not more than 3 s.

Air may be introduced in the side ducts so that the optics stay clean, within the given light attenuation drift requirements (see E.4.2). Pressurized air can be used instead of a self suction system.

A laser photometer system shall use a helium-neon laser with a power output between 0,5 mW and 2,0 mW.

Air may be introduced in the side ducts so that the optics stay clean, within the given light attenuation drift requirements (see E.4.2). Pressurized air may be used instead of a self suction system.

NOTE The optics should be regularly inspected and cleaned from smoke deposition whenever necessary.

The analysis of oxygen, and carbon dioxide, requires that any water vapour in the combustion gases shall be trapped by means of a suitable drying agent.

The analyser shall be of the paramagnetic type and capable of measuring a range of 16% to 21 % oxygen (K₀₂/K_o,_r). The noise and drift of the analyser shall be not more than 0,01 % (100 parts per million) over a period of 30 min as measured in accordance with E.2.3. The manufacturer’s declared response time of the analyser shall be not more than 12 s. The output from the analyser to the data acquisition system shall have a resolution better than 0,01 % (100 parts per million).

Continuous analysis of carbon dioxide shall be achieved using an IR spectrometer. The analyser shall be capable of measuring a maximum range of 0 % to 10 % carbon dioxide. The linearity of the analyser shall be 1 % of full scale or better and the manufacturer’s declared response time shall be not more than 12 s.

5. Qualification of test apparatus

   1. General

The checks in 5.2 to 5.5 shall be undertaken to qualify the apparatus.

NOTE In this document, the use of the terminology “calibration” mirrors that in EN 13823 (the SBI test). It is used in a generic way, in some cases referring to a true calibration procedure whilst in others referring to a series of checks which may, in other documents, be referred to as a verification.

The determination of the flow profile in the exhaust duct, in the vicinity of the probes, is required for two main reasons:

1. to check that the design of the exhaust duct gives an acceptable profile;

2. to determine a k_c which shall be compared with the k, obtained by the following calibrations.

Further information on how to perform this measurement is given in Annex D.

NOTE The value k_c should be approximately 0,86 for a 400 mm duct.

Measurements shall be performed by means of a calibrated hot wire anemometer (or other suitable instrument) moved along a vertical axis (OY) and then along a horizontal axis (OX) to obtain the vertical and horizontal air speed distributions inside the duct.

The velocity profile shall be measured at the same airflow rate as used during the actual test (see 6.6). Measurements at additional flow settings should be made and used to demonstrate the consistency of the velocity profile determination within the range of operation

Gas analysers take a finite time to respond to changes in gas concentrations. This is called the sampling delay time. The delay times shall be determined in order to synchronise the temperature, oxygen and carbon dioxide measurements. All data shall be corrected for any delay time before calculating the heat release. The delay time of the oxygen analyser shall be determined as the time difference between a 3 К change in the duct temperature and a 0,05 % change in the oxygen concentration. The delay time of the carbon dioxide analyser shall be determined as the time difference between a 3 К change in the duct temperature and a 0,02 % change in the carbon dioxide concentration.

Sampling delay times shall be determined before commissioning the apparatus and after each major change in the gas analysis system.

Before initial use of the apparatus and after each major change in the gas analysis system, exhaust flow measurement, gas and airflow measurement to the burner or smoke measurement, a series of calibrations shall be performed in order to

1. check the equipment, including any improvements adopted during the set-up stage or modification period;

2. determine a commissioning k_t factor to be used for daily testing;

3. check the stability of the smoke measurement system;

4. check the correct measurement of the white light measuring system.

The calibrations shall be carried out at different levels of HRR covering the range of heat releases that are expected when burning cables in a test, i.e. from about 20 kW to 200 kW. This is required in order to verify the linearity of the HRR measurement system. Further information on the HRR calibration and determination of the commissioning k_t factor is given in Annex E.

The procedure given in Annex E shall be carried out and its requirements met in order to calibrate and check the smoke measuring system.

NOTE It is recommended that the commissioning calibrations are carried out at least once per year depending on the frequency of use of the equipment.

Each testing day a calibration test shall be performed using the ignition source given in EN 60332-3-10. A calibration burn of at least 10 min shall be performed, using the heat output of the burner relevant to the test procedure to be used that day (i.e. 20,5 kW or 30,0 kW as appropriate). The calibration test shall be carried out without the ladder in the test chamber. The result of the calibration test shall be recorded for each testing date. Testing shall not be carried out unless the criteria given in 5.5.4 are met.

NOTE See E.2.2 and E.2.4 for the daily adjustment of the oxygen and carbon dioxide analysers

The calibration shall be performed in the following sequence:

1. a 5 min base line without the burner;

2. a further 10 min with the burner at the relevant heat output;

3. a further 5 min without the burner.

The following shall be calculated after the calibration test using the commissioning k, factor and the E-value for propane (16,8 MJ/m³):

1. the drift of the HRR, oxygen % and light intensity during the first 5 min;

2. the average calculated HRR during the last 5 min of the burning period;

3. the start values of oxygen %, carbon dioxide %, light intensity and HRR, each as the average during the first minute of the 5 min base line period;

4. the end values of oxygen %, light intensity and HRR, each as the average during the last minute of the calibration test;

5. the difference between start and end values of oxygen %, HRR and light intensity.

1. the average HRR during the last 5 min of the burner period shall be within ± 5 % of the set value of 20,5 kW or 30,0 kW;

2. the difference between the start and end values of oxygen % shall be less than 0,01 % (absolute value);

3. the difference between the start and end values of light intensity shall be equal to or less than 1 % transmission;

4. the difference between the start and end values of HRR shall be equal to or less than 2 kW;

5. the drift on the light intensity shall be less than 1 % during the 5 min before burner ignition;

6. the drift of oxygen % shall be less than 0,01 % (absolute value) during the 5 min before burner

ignition;

7. the drift on HRR measurement shall be less than 2,0 kW during the 5 min before burner ignition.

NOTE The drift of oxygen %, HRR and light intensity shall be calculated by means of a linear trend line during the 5 min before burning ignition.

5. Test procedure

   1. Initial test conditions

The test chamber and air supply temperature shall be in the range 5 °С to 40 °С.

The test sample shall comprise a number of test pieces of cable from the same production length, each having a length of (3,5^+o'o)m. The number of test pieces in the test sample shall be as determined according to 6.4.

The test pieces shall be conditioned for at least 16 h at a temperature of (20 ± 10) °С. All packaging shall be removed prior to conditioning. The test pieces shall be dry

.

The following formulae shall be used to determine the number of test pieces (TV) for the test.

NOTE The following formulae apply to circular cables. No mounting procedure for non circular cables has been defined. This is under consideration.

The number of test pieces, TV, is given by

.. . ( N = int

300 + 20'

C + 20 у

(1)

where

d_c is the measured diameter of the cable (in mm and rounded to the nearest mm

according to IEC rules);

int function the integer part of the result (i.e. the value rounded down).

The number of test pieces, N, is given by

.. . ( N - int

300 +

2< >

(2)

where

d_e is the measured diameter of the cable (in mm and rounded to the nearest mm

according to IEC rules);

int function the integer part of the result (i.e. the value rounded down).

A number of approximately 10 mm diameter bundles (N _bu) shall be mounted where

зоо+юЛ

20 J

= 15

(3)

N

bu

Thus 15 bundles shall be mounted.

The number of test pieces in each bundle (n) is:

n = int

100

(4)

where

is the measured diameter of the cable (in mm to one decimal place);

t

int function

he integer part of the result (i.e. the value rounded down).

The total number of test pieces (TV) will thus be:

rV = r?xl5 (5)

The test sample shall be mounted on the front of the standard ladder. The lower part of each test piece or bundle of test pieces shall extend between 200 mm and 300 mm under the lower edge of the burner face, dependent on their actual length, such that (3 300⁺²q) mm of the cables are above the lower edge of the burner face.

NOTE 1 The positive tolerance on the test sample length is to aid fixing on the ladder rung below the burner.

Each test piece or bundle of test pieces shall be attached individually to each rung of the ladder by means of a metal wire (steel or copper) using the crossed wire method of fixing shown in EN 60332-3-10, Figure 3. For cables up to and including 50 mm diameter, wire between 0,5 mm and up to and including 1,0 mm in diameter shall be used. For cables above 50 mm diameter, wire between 1,0 mm and 1,5 mm in diameter shall be used. For bundles, apply a metal wire around the bundle at each rung position before attaching the bundle to the rung with a further wire.

NOTE 2 It is recommended that a drilled plate be used as a guide to maintain the relative position of each test piece when installing a bundle of test pieces.

When mounting the test pieces, the first test piece or bundle of test pieces shall be positioned approximately in the centre of the ladder and further test pieces shall be added on either side so that the whole array of test pieces is approximately centred on the ladder.

NOTE 3 It is useful for additional information to draw, at each height of 25 cm, a horizontal line in order to estimate the flame spread as a function of time. The first line (i.e. zero line) should be at the same height as the burner.

The test pieces shall be mounted according to the cable overall diameter in accordance with Table 1

.

Table 1 - Mounting as a function of cable diameter

The test pieces shall be mounted in accordance with 6.5.1 except that at the back of the ladder, a non­combustible calcium silicate board shall be mounted. The board shall have a density of (870 ± 50) kg/m³ and a thickness of (11 +2) mm and shall be mounted all along the ladder and fixed to the rungs. This board shall have a width of (415 ±15) mm and a length of (3 500 ±10) mm and may be mounted in two or more parts (see Figure 9).

NOTE Guidance on availability of suitable backing boards is given in Annex H.

The board shall be dry and shall then be conditioned at a temperature of (20 ± 10) °С and a relative humidity of less than 70 % for a minimum of 48 h before testing.

The volume flow rate in the exhaust duct shall be set to a value of (1,0 ± 0,05) m³/s. The flow rate during the test shall be maintained in the range 0,7 m³/s to 1,2 m³/s.

NOTE 1 Due to changes in heat output, some exhaust systems (especially those provided with local fans) may need manual or automatic readjustment during the test in order to meet this requirement. If readjustment during the test is carried out, it is necessary to ensure that the measurement of heat release rate has not been influenced.

NOTE 2 The flow rate value of (1,0 ± 0,05) m³/s is based upon the use of an exhaust duct diameter of 400 mm. A lower value may be more appropriate for exhaust ducts of smaller diameter, provided it is sufficient to ensure collection of all the combustion products leaving the test chamber.

The ignition source shall be one ribbon-type propane gas burner in accordance with EN 60332-3-10.

For Class B1_ca the flow rate of propane shall be equal to a mass flow of (647±15)mg/s which corresponds with a nominal HRR of 30,0 kW. The air flow to the burner shall be (2 300 ± 140) mg/s.

For Class B2_ca, C^ and D_ca the flow rate of propane shall be equal to a mass flow of (442 ± 10) mg/s which corresponds with a nominal HRR of 20,5 kW. The air flow to the burner shall be (1 550 ± 95) mg/s.

NOTE 1 A net heat of combustion of 46,4 kj/g and an E-value of 16,8 x 10³ kj/m³ for the combustion of propane are used to calculate the propane flow rate

NOTE 2 An analysed HRR value of 30,7 kW or 21,0 kW respectively results when analysing the HRR from the ignition source using the average E-value of 17,2 x 10³ kJ/m³ used in this test (see Annex A).

NOTE 3 The use of mass flow meters and controllers is strongly recommended to achieve the required propane and air flow rates.

The positioning of the ignition source for the test shall be in accordance with EN 60332-3-10.