Fire Cause 1

[koshyeng]

Sir,

An organic compound with specific heat of 0.39 BTU/lb-deg F

awith flash point of 245 F and auto ignition temperature of 850 deg F caught fire when it was trapped between a thermal insulator and an electric heater connected to a processing equipment with operating temperatures at 400 deg F and electric heater at 500 deg F. Heater temperature will not go above 550 as it has an interlock at this temperature.

What is the possibility of this oragnic compound catching fire? Can the material reach up to its autoignition temperature and burn? There was no ignition source or what so ever when the material caught fire. Continuity of wiring and grounding is intact (verified).

Thank You

 

[25362]

Spontaneous combustion and fires may start as a result of exothermic autoxidation, such as when thermal insulation over heated piping or equipment becomes saturated with an organic liquid of low volatility. The evolved heat energy is not removed by vaporization, leading to autoignition.

 

[CH5OH]

possible scenario (?):
1.heater's pressure drops from operating pressure to atmospheric
2.liquid boils of until vapour pressure is reached
3.submerged heater controller and safety sensor stay submerged, heater keeps adding heat
4.top heater element is no longer submerged and temperature surrounding vapour raises above auto ignition temperature
5.shell looses its boundry and superheated steam (above auto ignition) is contacted with air.
6.shell boils empty and controller cuts out heater
7.fire brigade puts out the fire.
or?
you mean soaked insulation material caught fire @ 500degC?

http://www.lloydminsterheavyoil.com/safety.htm

 

[unclesyd]

It has been known for some time that saturated insulation, especially Calcium Silicate will cause lowering of the A.I, of organic compounds by varying degrees. It has been determined that the insulation can be catalytic in respect to spontaneous combustion. A large chemical company in Deer Park TX. had a major fire from hydraulic fluid spontaneously ignited and the resultant small fire caused the insulation on some large lines to fail, another story. The failure of these lines created the major fire.
A lot of work, not published, was done by our Safety and Fire Protection Group prior to and post the Deer Park fire. The work was mainly concerning thermal heating fluids due to our high temperature operations. The results were essentially to fix the leak and remove the damaged insulation. If I recall correctly the lowering of the A.I. brought it well below our normal operating temperature.

I may stand corrected but I think the authors of the first reference where involved with fire mentioned above.

http://www3.interscience.wiley.com/journal/109077335/abstract?CRETRY=1&SRETRY=0

http://www3.interscience.wiley.com/journal/109077035/abstract

One other avenue to fires as you describe comes from the heating element itself. If an elements temperature isn't controlled internally or limited by a wiring scheme the surface of the element can see a much higher temperature than indicated on a area controller.
We have hundreds of heating elements (CalRods) that are controlled by wiring in such away that limits their skin temperature to a max, our operating temperature. In this case the elements are capable of 1500F and our operating temperature is 600F.

 

[koshyeng]

Thanks unclesyd.

Apparently upon investigation (initial investigation), I found that this organic compound has AIT of 653 deg F. Infrared camera showed maximum localized temperatures (hot spots) to be 663 deg F. This will self explain the cause of fire.

However, I will test our insultaion material saturated with organic compound for AIT.

Appreciate if you could shed some light on your statement " heating elements (CalRods) that are controlled by wiring in such away that limits their skin temperature to a max" through references. For educational purposes


Thank You.

 

[unclesyd]

This is out of area but as I remember it there was a phrase "series limited" use when talking about a set of elements. In our case it was a set of 12 to 15 18" long elements embedded an Al cozy that surrounded an external polymer gear pump. These elements were wired so the Al cozy temperature would never be above 600F.

Maybe some of the sparkies will chime in as I'm of the plug in and tune for maximum smoke school,

We kept this heater arrangement even tough we had the latest in control systems (Provox)