Nitrogen Explosion in Kansas

News reports (see here and here for instance)  out of Wichita, KS today described a ‘nitrogen explosion’ at an aircraft manufacturing facility. A security video from a nearby facility shows the rapidly expanding vapor cloud and flying debris. As many as 14 people have apparently been injured, but no fatalities were reported.

Incident

Reports indicate that a 3” liquid nitrogen line ruptured inside of the plant. No fires were reported. The resulting incident also damaged a nearby liquid nitrogen storage tank. Due to the holidays and the resulting reduced staffing, no one was near the site where the rupture occurred.

Commentary

While the expanding vapor cloud and flying debris looked impressive and caused significant amounts of damage, what happened cannot really be called an explosion since there was no detonation or fire associated with the incident. What happened was that cryogenic (very cold) liquid nitrogen escaped containment when the 3” line ruptured. As the liquid entered the atmosphere it rapid warmed and boiled. The liquid expanded into a vapor cloud with 694 times the volume previously experienced in the liquid state.

This rapid expansion during the phase change caused an area of high pressure that was lightly contained by the walls of the building. As the pressure rapidly rose, the walls were no longer able to contain the pressure and were blown outwards.

Neither liquid nitrogen nor nitrogen gas are chemically reactive enough (in fact they are generally considered to be inert, or non-reactive) to cause an explosion. If a similar volume of a chemically reactive substance were to explode a large flame wall and much more damage would have resulted.

Having said that, situations such as this are very dangerous and significant damage was done to the building and people were certainly injured. What was not noted in any of the articles that I have seen was that there was also a potential risk for asphyxiation near the leak as the expanding nitrogen cloud displaced oxygen from the immediate area. There was also a potential for severe cold injuries in the immediate area of the leak. From the articles that I have seen it does not appear that anyone was near enough to the initial leak for these to have been a problem.

The white cloud seen in the incident photos and videos was not actually a nitrogen cloud. Nitrogen is colorless and odorless (and actually makes up about 78% of the atmosphere). The visible vapor cloud is water in the atmosphere that has been super cooled by the still very cold nitrogen gas to form a cloud.