Criteria for and Verification of a Permanent or Temporary Total Enclosure – USEPA Method 204

USEPA Method 204 is utilized to determine whether a permanent or temporary enclosure meets the criteria for a total enclosure.  An existing building is used as a temporary or permanent enclosure as long as it meets the appropriate criteria described in this method.
 
An enclosure is evaluated against a set of criteria.  If the criteria are met and if all the exhaust gases from the enclosure are ducted to a control device, then the volatile organic compounds (VOC) capture efficiency (CE) is assumed to be 100 percent, and CE need not be measured.  However, if part of the exhaust gas stream is not ducted to a control device, CE must be determined.
 
The criteria for a temporary total enclosure are:

• any natural draft opening (NDO) is at least four equivalent opening diameters from each VOC emitting point;
• any exhaust point from the enclosure is at least four equivalent duct or hood diameters from each NDO;
• the total area of all NDO's shall not exceed 5 percent of the surface area of the enclosure's four walls, floor, and ceiling;
• the average facial velocity (FV) of air through all NDO's shall be at least 3,600 m/hr (200 fpm).  The direction of air flow through all NDO's shall be into the enclosure; 
• all access doors and windows whose areas are not included in the method and are not included in the calculation are closed during routine operation of the process.

The criteria for a permanent total enclosure:

• any NDO is at least four equivalent opening diameters from each VOC emitting point;
• the total area of all NDO's shall not exceed 5 percent of the surface area of the enclosure's four walls, floor, and ceiling;
• the average facial velocity (FV) of air through all NDO's shall be at least 3,600 m/hr (200 fpm).  The direction of air flow through all NDO's shall be into the enclosure; 
• all access doors and windows whose areas are not included in the method and are not included in the calculation are closed during routine operation of the process;
• all VOC emissions are captured and contained for discharge through a control device.