Essential knowledge for wire and cable inspection - Smoke density test

I. Inspection Purpose

When a fire breaks out, the smoke produced is very thick and highly toxic, posing a great threat to people's lives and safety. When wires and cables are burning, they also produce smoke. Currently, many projects require low-smoke and halogen-free cables. This test is an important one for evaluating the low smoke performance of cables.

Ii. Scope of Application

It is applicable to the determination of smoke density when cables are burning under specific conditions.

Iii. Inspection Basis

GB/T 19666—2019

GB/T 17651—2021

Iv. Test Equipment and Apparatus

1. Combustion chamber: Combustion chamber size: 3000±30mm cube.

2. Optical measurement device.

3. Standard fire source.

V. Sampling and Sample Preparation

1. Sample: The sample should consist of one or more cables or optical fibers of 1m±0.05m in length that have been carefully straightened. The sample should be treated at 23℃±5℃ for at least 16 hours.

2. Selection of the number of sample pieces: Select in accordance with the requirements stipulated in the standard.

3. Installation position of the sample: The cable, optical cable or cable bundle sample should be placed horizontally close to each other and at the center above the alcohol tray. The distance between the lower surface of the sample and the bottom of the alcohol tray should be 150mm±5mm.

Vi. Test Procedures

Before the test begins, immediately measure the temperature of the combustion chamber at a height of 1.5m to 2.0m from the ground and a minimum of 0.2m from the wall inside the door. The temperature should be within the range of 25℃±5℃.

2. If necessary, a blank test can be conducted before the test to preheat the combustion chamber.

3. Prepare the fire source for the test.

4. Install the sample, start the fan and ignite the alcohol. Close the airtight door of the combustion chamber.

5. If the light transmittance no longer decreases 5 minutes after the fire source is extinguished or when the test duration reaches 40 minutes, it can be considered that the test has ended.

6. Record the minimum light transmittance.

Vii. Evaluation of Test Results

The minimum light transmittance of cables or optical cables when burning should comply with the relevant standard provisions.

2. In disputed situations, similar cables or optical cables should be taken for two more tests, and the results of both tests should meet the requirements of Article 7.