We would like alert all on a recent fire incident we had. Fire broke out on one of the engine jacket water heater. As simple as the device is, there is potential for fire if item is not installed per OEM recommendation. This might be an oversight on the engine manufacturer. Heater oem is watlow. The heater comes in a bottle form with a built in thermostat. We learnt after the fire incident that oem states the capilliary tube type thermostat may fail in close position in high heat condition, and this is stated in their new installation guideline “disclaimer”. The end user is suppose to install additional high temperature cut off with manual reset, naturally. Unfortunately, this was not how the engine manufacturer package their standard engine.*
In our case, it looks like the top outlet isolation valve was left in a close position. Which probably cause an air/water lock. The heater over time would have boil off some water causing an air pocket on the top part of the heater bottle. This may have exposed the heating element to air instead of fully submerging. These heater type has surface temperature in eccess of 200 to 300 degC. What we think happenes then is heat causes failure on the thermostat to fail on. The thermal runaway then causes the overhead heater wiring to burn up and insulation catches on fire. Fortunately, the fire detector picks up and was attended to immediately. The caution here is any cable can catch on fire if exposed to high enough temperature. Eventhough the cable used is fire retardant.
So check that all heating element for any medium have a secondary high temperature cut off with manual reset. Classification society covers installation for oil medium. Not necessary for other medium such as water on engine jacket. Check also on hpu units, ventilation heaters, hotel water heater, etc.*