3 Meter Cube Smoke Chamber

(IEC 61034; BS 6853; BS 6724; BS 7622)

The 3 Metre Cube is used for measuring smoke emission when electric cables are burned under defined conditions, for example, when several cables are burned horizontally. The tests are carried out in a cubic enclosure, a photometric system is used to measure increase in smoke density.

This unit was developed by London Transport scientists in England and is designed to replicate the fire conditions found in enclosed spaces (such as an underground tunnel).

These units are produced to meet the specification used in many electric cable tests including IEC 61034. It permits the comparison between the standard absorbance of airborne particulates evolved under the specified conditions of each test method. The variables include thermal characteristics, form, dimensions and positions of the test piece.

The unit can be supplied in a self-assembly kit form or can be fully installed by FTT Engineers. The unit is made of steel sheet panels and can be supplied with customised extraction facilities and all instrumentation, fans, stands and sample mounting frames. The photometric system has a horizontal optical path of 3 m between two opposite faces of the cube and the attenuation of light transmitted through the chamber is measured during the test.

Features and Benefits

The enclosure is constructed from Zintec sheet steel of 0.8 mm thickness fixed to a steel framework. A door with a window enabling observation is placed at the front of the cube, with sealing at all appropriate joints.

Sealed windows (100mm × 100mm) are provided in the two laterally opposed faces for the transmission of light from the horizontal photometric system (source and receiver). The centres of these windows are situated at a height of 2.15m.

The photocell receiver is mounted at one end of a 150 ± 10mm tube with a dust protection window at the other end.The inside of the tube is matt black to minimise reflections. The signal from the photocell is proportional to the transmission of light and is recorded continuously during the test, using a chart recorder or data acquisition system.

The walls of the cube at floor level have orifices for atmospheric pressure equalisation. In order to avoid stratification of smoke, homogenisation is achieved by a fan placed on the floor inside the cube which blows horizontally throughout the test.

The method was developed for electric cables, but can be adapted also to materials, equipment and components.

3M Cube Software (CubeCalc)

A Microsoft Windows based user friendly software interfaces with the 3 Metre Cube Chamber via a multichannel A/D board. One channel monitors the transmission output from the photocell via an interface box.

  • The Software has the following features:
  • Calibration of the Photometric System
  • Specimen Information such as:
    • laboratory name
    • specimen description, diameter and number of cables tested
    • test name
    • data file name
    • time interval for processed data
    • conditioning environment
  • Test Run: Data is collected and displayed during the course of the test. The information is displayed in both graphical and textural form.
  • The following experimental data is processed after the test:
    • time, t
    • transmission at t
    • absorbance at t
  • A test report can be produced and printed after a test.

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