I have seen this same scenario 3x before, although the pump did not melt the housing through. The oxygen content was not measured at the time, I believe that it is not the root cause. The facilities are smaller and did not have high surgery cases or COVID patients at the time of failure.
This is what I believe happened to the pumps:
1) 1 or multiple exhaust filters fell out of its slot and was sitting in the pump housing. (see pictures, one filter fell out and was touching the pump housing).
2) This allowed all the oil to run out of the exhaust through oil vapor (some oil residue could be present on the roof).
3) Pump ran almost completely out of oil. Normally this would trip high temp and shut the pump off, in all 3 of my experiences the pumps either did not have a high temp cut off or it had failed to initiate. The facility staff measured the housing at over 600 degrees in one case after the incident.
4) The oily filters touching the housing became the fuel, the heat created the ignition with the oil, and the exhaust being open to atmosphere and pushing through at minimum atmospheric air was enough oxygen to create a fire out of the exhaust filters.
Even if the pump is properly maintained, I have seen exhaust filters fall out due to worn out clips or improperly installed.
The oxygen enriched exhaust could have made the fire burn hotter than normal but is likely not the root cause. The extra quantity of exhaust filters in your scenario would have burned longer which is why the housing melted through.
Curious to know, did the pump have a high temp shut down installed? Have the filters clips been replaced before or how long ago was that?
