Pay attention to whether there is flammable gas during welding

1. Accident process

A chemical plant has a deep-cold hydrogen production device several stories high. Due to pipeline leakage, welding is required. The pipeline passes through a small house. For safety reasons, nitrogen is first used to purge the house to replace and discharge the hydrogen, and then the explosion tester is used to pass the test. However, when the test was conducted again before welding, it was found that the hydrogen concentration had risen again to the explosion limit. After repeated inspections, it was found that the leaked hydrogen not only diffused in the small house, but also penetrated into the pearl sand, the insulation material of the pipeline. Then nitrogen was used to purge and replace again. After passing the test, the sand in the part where the hydrogen diffused was covered with a wet sack prepared in advance, and then welding was carried out. Soon after the operation began, an explosion occurred, destroying the house and the hydrogen production device several stories high, causing 7 deaths, 8 injuries, 6 hospitalizations, and a loss of 550,000 yuan.

2. Analysis of the main causes

Since hydrogen is the lightest gas, the wet sacks could not prevent hydrogen from diffusing out of the pearl sand. The hydrogen concentration in the small house continued to rise, and the conditions for ignition changed. The explosion occurred because the hydrogen concentration reached the explosion limit.