What is a good guideline for C1D2 rooms for ethanol extraction and who regulates this decision?
The Authority having jurisdiction (AHJ) over your facility is typically your city or county inspector. Keep in mind that there are other important stakeholders such as your insurance adjuster.
The first step in understanding the requirements for special electrical classification such as C1 D1 or D2 is to understand the building type and the occupancy for your facility. The amount of solvent that you have in storage, open use, close use, is regulated and will vary depending upon the building type and the occupancy for your facility.
The amount that you have in storage is also highly dependent upon the classification of the solvent that you are storing or using. For example there is no limit on CO2 for any occupancy or building type. On the other hand, the amount of ethanol that you can have in a facility is limited by the occupancy and the building type. A general rule of thumb is that no more than 240 gallons of ethanol can be stored per control area with a TYPE II building. There are a maximum of three control areas per building.
When the amount of solvent that is stored or in use within a facility exceeds the occupancy, the occupancy must be changed to a hazardous location occupancy. This comes with many building requirements. A good rule of thumb is that a hazardous occupancy will cost around 200 to $250 per square foot to build whereas a F2 occupancy which is a standard industrial occupancy will cost around $63 per square foot to build. Of course those numbers change across the country so it is important that you check with your architect on Standard Building cost before you decide which extraction method to use.