BS EN 60754-1 and -2: Gases from Burning Cable Materials

What it covers

The IEC 60754 series tests the gases given off when cable materials burn. It was developed because acid gases from some insulation and sheathing compounds can badly damage electrical and electronic equipment that is not itself involved in the fire.

All three parts test individual materials taken from a cable, such as the sheath or insulation, not a complete cable. The relevant cable standard says which components to test. The standards note that a test on raw materials alone should not be used to declare cable performance.

Part 1: halogen acid gas content

• A material sample is heated in a quartz tube inside a tube furnace, with a controlled air flow.
• The gases are bubbled through gas washing bottles and the solution is analysed to find the amount of halogen acid.
• The result is expressed as milligrams of hydrochloric acid per gram of test specimen.
• The method cannot measure hydrofluoric acid. The standard points to IEC 60684-2 for that.
• For reasons of precision, the method is not recommended for reporting values below 5 mg/g of sample.

5 mg/g equals 0.5%. This is why many “halogen free” or LSZH cable specifications state a halogen acid gas content of ≤ 0.5% to IEC 60754-1. It is the lowest level the Part 1 method can report with confidence, not proof of zero halogen.

The 2011 edition added a blank test procedure, better guidance on specimen preparation and heating, and an informative annex on testing a sample representative of a whole cable construction.

Part 2: acidity and conductivity

• The material is burnt in a quartz tube at a boat position temperature of 935 °C to 965 °C for 30 min under a controlled air flow.
• The gases are absorbed in distilled or demineralised water and the pH and conductivity of the solution are measured.
• A low pH indicates an acidic, more corrosive effluent. A high conductivity indicates more dissolved ionic material.
• The general method tests each component and gives formulae for a weighted value for the combination of materials in a cable.
• A simplified method is provided for quality control, where only compliance with a stated limit needs to be shown.

The standard says the method is an indirect assessment of corrosivity. Its recommended limits are an indication only, because the link between corrosion and these two parameters does not hold for every material.

Recommended performance requirements are given in informative Annex A. Cable datasheets commonly quote pH ≥ 4.3 and conductivity ≤ 10 µS/mm to IEC 60754-2.

Part 3: low halogen levels by ion chromatography

• Uses the same heating procedure as Part 2, then analyses the solution by ion chromatography to ISO 10304-1.
• Reports chlorine, bromine, fluorine and iodine separately, so it can detect fluorine, which Part 1 cannot.
• Intended for materials with an individual halogen content of no more than 10 mg/g.
• Not recommended for values below 0.1 mg/g of sample.

Part 3 fills the gap below the 5 mg/g limit of Part 1 and is useful where a specification needs evidence of very low halogen content.

Use under the Construction Products Regulation

For cables in classes B1ca, B2ca, Cca and Dca, EN 13501-6 gives an additional acidity class based on EN 60754-2:

So a cable classed B2ca-s1a,d1,a1 has passed the strictest acidity class. Note that the CPR acidity class uses Part 2 only. It does not use the Part 1 halogen acid gas figure.

What to check on a datasheet or test report

• Which part was used. A “halogen free” claim should state IEC 60754-1 (≤ 0.5%) or IEC 60754-3 results, and acidity should state IEC 60754-2 pH and conductivity.
• Actual values with units: % or mg/g for Part 1, pH and µS/mm for Part 2.
• For Part 2, whether the result is a weighted value for the whole cable or a single component.
• For CPR cables, the declared acidity class (a1, a2 or a3) on the declaration of performance.
• That the requirement in the project specification is met, as the IEC test methods themselves leave limits to the cable specification.

Related reading: What is LSZH cable and when do you need it?.