Abstract: Abstract: In the cable shaft, the cables are usually arranged in bundles, which has a great influence on the fire risk. Therefore, it is of great significance to study the influence of the number of cables laid on the vertical fire spread. For this reason, by using the self-designed fire spread experimental platform, the WDZ-YJY cables are arranged in different quantities, and the parameters of pyrolysis, spreading and dripping are studied and analyzed. By analyzing the experimental results, the vertical downstream fire spread of cables can be divided into three stages: ignition stage, smooth transition stage and rapid development stage. Study found that the combustion with more cables haven't spend more time, but extend fire scale. Among them, after the pyrolysis front is higher than 30 cm, the maximum fire spread rate when the number of cables is 3 and 4 exceeds the maximum fire spread rate of 1 and 2 cables by 200%. On the one hand, the mass loss rate of cables is higher in the working condition of multiple cables, and the peak mass loss rate of 4 cables is 142% higher than that of 2, reaching 2.39 g/s, showing that more cables have more pyrolytic products, making the combustion more intense, and the unburned cable above can obtain more heat; On the other hand, the results show that the peak radiant heat flow of 4 cables reaches 2.46 kW/m2, which is 70% higher than that of 2. The dripping will increase the spreading downstream, while the dripping duration during combustion of a heavily laid cable bundle is significantly longer.

Key words: Key words: offshore booster station, cable, vertical fire spread, mass loss rate, fire spread rate