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BS EN 50267 Common test methods for cables under fire conditions

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BS EN 50267 Common test methods for cables under fire conditions

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									BS EN 50267: Common test methods for cables under fire
conditions – Tests on gases evolved during combustion of
                  materials from cables


                                             Contact Details: Reaction to Fire

                                             Phone: +44 (0) 1925 655116
                                             Fax: +44 (0) 1925 646672

                                             Email rtfinfo@warringtonfire.net
                                             Web: www.warringtonfire.net




Why Test for Halogen Acid Gas Emission and Degree Of Acidity of Gases?

In the event of a fire many fumes are produced. Significant discussions surround the issue of
smoke emissions from burning cables. This test is concerned with the possibility of corrosive
acid gases being released from halogen containing cables and the damage such gases can
cause (eg. to computer equipment).


Test Method

BS EN 50267-2-1: 1999 “Common test methods for cables under fire conditions –
Tests on gases evolved during combustion of materials from cables – Part 2-1:
Procedures – Determination of amount of halogen acid gas”
Burn procedure: Between 0.5 and 1g of material is placed into a tube furnace. Over a period
of 40 minutes, the temperature inside of the tube furnace is steady increased to 800°C, the
temperature is then maintained for a further 20 minutes. The gases produced are absorbed
into a defined catch solution, which is later made up to one litre and then analysed.

Analysis method: The standard states that the amount of halogen acid evolved (except
hydrofluoric acid) should be expressed as hydrochloric acid. It is noted that the analytical
method described in the standard to determination the amount of halogen acid contained
within the test solution is a titration method. The standard specifies that other analytical
methods may be used having at least the same accuracy. Bodycote warringtonfire
utilised ion chromatography to measure the concentration of halogen acid. The ion
chromatography method employed by Bodycote warringtonfire has a limit of detection
and limit of quantification much lower than 5mg/g, which is the value defined in the
standard for the titration method described.

The titration method would be unable to specify whether the gases produced were hydrogen
chloride or hydrogen bromide, it is for this reason that the standard required the total
amount of halogen acid to be expressed as hydrochloric acid. Since Bodycote
warringtonfire use ion chromatography, we are able to specify the concentration of
hydrogen bromide and hydrogen chloride independently, these values are then combined.

Performance requirements: No further guidance is provided on performance requirements.
BS EN 50267-2-2: 1999 “Common test methods for cables under fire conditions
– Tests on gases evolved during combustion of materials from cables – Part 2-2:
Procedures – Determination of degree of acidity of gases for materials by
measuring pH and conductivity”

Burn procedure: 1g±0.005g of material is placed into a tube furnace. The temperature
inside of the tube furnace where the sample sits is 935°C, the specimen remains in the
tube furnace for a period of 30 minutes. The gases produced are absorbed into a defined
catch solution, which is later made up to one litre and then analysed.

Analysis method: The standard states that the pH and conductivity of the test solution
should be measured, using calibrated pH and conductivity meters.

Performance requirements: No requirements for conformity are included in this standard.
The standard does however state:
“Where no requirements are specified in the particular cable specification, and where the
cable is described as “zero halogen” or halogen-free” it is recommended that at least both
of the following requirements should be met for each of the individual materials of a cable
construction.
    a) The pH value as determined in 6, should not be less than 4.3 when related to one
        litre of water”
    b) The conductivity value as described in 6 should not exceed 10µS/mm when related
        to one litre of water


BS EN 50267-2-3: 1999 “Common test methods for cables under fire conditions
– Tests on gases evolved during combustion of materials from cables – Part 2-3:
Procedures – Determination of degree of acidity of gases for materials by
measuring pH and conductivity”

Burn procedure: 1g±0.005g of material is placed into a tube furnace. The temperature
inside of the tube furnace where the sample sits is 935°C, the specimen remains in the
tube furnace for a period of 30 minutes. The gases produced are absorbed into a defined
catch solution, which is later made up to one litre and then analysed.

Analysis method: The standard states that the pH and conductivity of the test solution
should be measured, using calibrated pH and conductivity meters. The results from the
different components of a cable are then weighted.

Performance requirements: No further guidance is provided on performance requirements.


When Is This Test Conducted?

This test is called upon in several cable specifications, one example being in order to term
a material halogen free in accordance with BS EN 50306-1: 2002 “Railway Applications –
Railway Rolling Stock cables having special fire performance – Thin Wall – Part 1: General
Requirements” (in addition to a fluorine content test).


Specimen Requirements

50g of each component which is to be assessed.

								
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