| Full title | Measurement of smoke density of cables burning under defined conditions. Part 2: Test procedure and requirements |
| Publisher | IEC (TC 20); adopted as EN by CENELEC and as BS EN by BSI |
| Current edition | IEC 61034-2:2005+AMD1:2013+AMD2:2019 (edition 3.2); BS EN 61034-2:2005+A2:2020 |
| Status | Current. Group safety publication under IEC Guide 104 |
| Companion part | IEC 61034-1 (EN 61034-1): Test apparatus |
| Related standards | EN 13501-6, EN 50575, EN 50399, IEC 60754 series |
What it covers
IEC 61034 sets out a method for measuring the density of smoke given off by electric and optical fibre cables burning under defined conditions. The result is expressed as the minimum light transmittance recorded across the test chamber.
The standard comes in two parts:
- Part 1: Test apparatus. The 27 m³ test enclosure, the photometric system, the fire source, the smoke mixing method and a qualification procedure.
- Part 2: Test procedure and requirements. How to select, prepare and mount the cable test pieces, how to run the test and how to evaluate the result. It includes an informative annex with a recommended performance requirement.
The standard itself notes that the cable arrangement in the test may not represent real installation conditions. It is a comparative test, not a model of a real fire.
The test apparatus (Part 1)
| Item | Requirement |
|---|---|
| Enclosure | Cube with inside dimensions of 3 000 mm ± 30 mm (27 m³) |
| Light path | Horizontal beam through sealed windows on two opposite walls, centred 2 150 mm ± 100 mm above the floor |
| Ventilation | At least two orifices at floor level, total open area 50 cm² ± 10 cm² |
| Fire source | 1 litre of alcohol burnt in a metal tray |
| Smoke mixing | A defined mixing method distributes the smoke through the cube |
Test procedure (Part 2)
Preparing the sample
- Each test piece is 1.00 m ± 0.05 m long, straightened and conditioned for at least 16 h at 23 °C ± 5 °C.
- The overall diameter is measured at three places at least 1 m apart, and the average decides how many test pieces are used.
- Test pieces or bundles are laid touching, horizontally, centred over the tray, with 150 mm ± 5 mm between the underside of the sample and the bottom of the tray.
Number of test pieces
| Overall cable diameter (D) | Test sample |
|---|---|
| D > 40.0 mm | 1 test piece |
| 20.0 mm < D ≤ 40.0 mm | 2 test pieces |
| 10.0 mm < D ≤ 20.0 mm | 3 test pieces |
| 5.0 mm < D ≤ 10.0 mm | N = 45 / D test pieces, rounded down |
| 1.0 mm ≤ D ≤ 5.0 mm | Bundles of 7 twisted test pieces; number of bundles = 45 / (3D), rounded down |
Non-circular (flat) cables are tested as a flat horizontal unit with the minor axis facing the fire. The standard gives rules for calculating an equivalent diameter from the axis ratio.
Running the test
- Before the test, the air temperature in the cube must be 25 °C ± 5 °C. A blank test may be run first to preheat the enclosure.
- The air circulation is started and the alcohol is lit. Everyone leaves the cube and the door is closed.
- The test ends when there is no further fall in light transmittance for 5 min after the fire has gone out, or when the test reaches 40 min.
- The minimum light transmittance is recorded as a percentage: It / I0, transmitted light over incident light.
Evaluating the result
- The pass value is set by the relevant cable specification, not by IEC 61034-2 itself.
- If the cable specification gives no value, the standard recommends adopting the value in its informative Annex B as a minimum.
- For cables up to 80 mm diameter, the recorded minimum transmittance is the cable result. Above 80 mm, the result is multiplied by D/80.
- In case of dispute, two further tests are run on similar cables and both must comply.
Many low smoke zero halogen (LSZH) cable datasheets quote a minimum light transmittance of 60% to IEC 61034-2. Check the cable specification for the figure that actually applies.
Use under the Construction Products Regulation
Under the CPR, cables in classes B1ca, B2ca, Cca and Dca receive a smoke class from EN 50399 (total smoke production and peak smoke production rate). EN 13501-6 then uses EN 61034-2 to split class s1 into two sub-classes:
| Smoke class | Criteria |
|---|---|
| s1 | TSP1200 ≤ 50 m² and peak SPR ≤ 0.25 m²/s (EN 50399) |
| s1a | s1 and light transmittance to EN 61034-2 ≥ 80% |
| s1b | s1 and light transmittance to EN 61034-2 ≥ 60% and < 80% |
A cable declared as s1a, for example in a classification such as B2ca-s1a,d1,a1, has therefore passed the 3 m cube test at 80% transmittance or better.
What to check on a datasheet or test report
- The standard and edition quoted, for example BS EN 61034-2 or IEC 61034-2.
- The measured minimum light transmittance as a percentage, not just “pass”.
- Whether the figure meets the requirement in the project specification or cable standard.
- For CPR cables, whether the declared smoke class is s1a or s1b, which tells you the 3 m cube result band.
Related reading: What is LSZH cable and when do you need it?.