Auto Ignition Temperature in Class I Div. I

[fifty60]

Per 501.135 I have to limit heater temperature to 80% of the auto ignition temperature (AIT). This is only applicable to Class 1 Div II chambers.

For Class 1 Div I, is there no limit requirements for how close you can get to the auto ignition temperature? If I am using hot oil heating, for example, can I raise the temperature of the hot oil to anywhere below the AIT?

Not that I think that is a good idea, just would like to know if there are exact limits like what are stated in 501.135 (B)1

 

[bobgorno]

Per 501.135 I have to limit heater temperature to 80% of the auto ignition temperature (AIT). This is only applicable to Class 1 Div II chambers.

For Class 1 Div I, is there no limit requirements for how close you can get to the auto ignition temperature? If I am using hot oil heating, for example, can I raise the temperature of the hot oil to anywhere below the AIT?

Not that I think that is a good idea, just would like to know if there are exact limits like what are stated in 501.135 (B)1

Are you confusing electrical external surface temperature (T-code) with process fluid operating temperature?

BobG

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[fifty60]

The T Code is referring to the maximum temperature of any exposed surface, as required by 500.8(B)1, right?

So can the actual process fluid temperature be any temperature, as long as the surface temperature is below the AIT?

 

[bobgorno]

The T Code is referring to the maximum temperature of any exposed surface, as required by 500.8(B)1, right?

So can the actual process fluid temperature be any temperature, as long as the surface temperature is below the AIT?

It's important to note that 500.8 is referring to electrical equipment. A hot surface of a fired heater for example is handled differently. See NFPA 497 or API RP500 regarding coninuous ignition sources. For your electrical equipment you might post a few more specifics for the group to respond to.

It's not always as simple as we hope and there can be many things to consider.

Generally the hot oil in heat transfer systems may be heated above their flash points but not necessarily above the AIT.

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[csc_wyo]

API RP 2216

API RP 2216

Do your research for your specific situation, but I've used API RP 2216 before to justify a few designs and installations. :thumbsup:

From API RP 2216 (2003)
1.2 - "...it is generally recognized by the petroleum industry that hot surfaces, even at temperatures considerably above the auto-ignition temperatures of the hydrocarbons involved, are not always capable of igniting flammable vapor-in-air mixtures."

5.2 - "...In general, ignition of hydrocarbons by a hot surface should not be assumed unless the surface temperature is approximately 360 deg F above the accepted minimum ignition temperature of the hydrocarbon involved."