NEC and API 500

[cirtcele]

If we follow NEC, there is no permission for reducing the Class I Division I requirements. But according to the API 500, the area classification for gas can be eased up from Class I Division I to Class I, Division II, if the area is adequately ventilated. “Adequate ventilation” is defined in API as at least 6 changes of air per an hour. If 6 times air circulation in an hours is difficult to achieve then API offers two alternatives:

Alternative 1: The maximum release of the gas under the worst condition is to be calculated; it is then possible to calculate the minimum number of air changes required to dilute the gas to below 25% of the lower flammable limit. This ventilation figure must be multiplied by a factor 4 to get the required adequate ventilation. This figure may be used as criteria for adequate ventilation even if it is less than 6 changes of air per hour.
Alternative #2: If gas detection system is set up to alarm at 20% of the lower flammable limit (or turn on additional fans) and shut down all electrical equipment not suitable for Division I location when the concentration reaches 40% of the lower flammable limit.

My understadning from the above is if our client agrees to use API then using gas detectors can reduce the area clasification. Am I right?

 

[JLSeagull]

The NEC provides relief for the ventilation fan motor if the only reason for the Division 1 classification pertains to inadequate ventilation. See article 500.7 (K)(1). The gas detectors must be rated Division 1. Several fine print notes refer to API, ISA and NFPA standards. I would assure NEC compliance.