Furnish and install a packaged Micro-Filter III(tm) dual fan filter/pressurization unit is ETL certified by Intertek Testing Services to be in conformance with applicable UL and CSA codes and standards for Class I, Groups C & D, Division I hazardous locations (Division II or general purpose optional). The unit shall include spark proof direct drive dual fans, primary and secondary fan backdraft dampers, internal balance damper, four stages of chemical/particulate filters and remote alarm relay. Unit options shall include stainless (galvanized) steel stack with rain cap and birdscreen, gas dectection relay and stack shutoff damper/motor.

Provide 30 percent efficient pleated throwaway filters for stages one and three. Provide replaceable media chemical filters for stage two with stainless steel filter cartridges (two) and front/rear access so that filter media can be changed from outside the building using a forklift. Provide high performance, preformed, deep pleated disposable type filter for stage four with an average efficiency of 60-65% (optional 90-95% efficient filter available) on ASHRAE test 52-76. It shall have an average arrestance of not less than 97%. Stage two shall have a Micro-Seal(tm) system to assure 100 percent air filtration with no air by-pass around filters.

The unit cabinet shall be constructed of 16 gauge galvanized paint grip (optional stainless) steel and coated with two coats of Sherwin-Williams Polane(r) T Polyurethane Enamel.

Necessary unit controls shall power up the primary pressurization fan while enabling the secondary purge fan to provide a safe start-up/purge. Provide adjustable stainless steel internal balance damper field set to maintain 0.1 inches of w.c. building pressure to prevent contaminants from entering pressurized area. If a door is opened , the secondary purge fan shall be capable of providing 60 FPM exit velocity to meet the NFPA 496 code. Provide unit mounted magnehelic building pressure gauge, filter pressure drop gauge, explosion proof indicating light for "pressure OK" (green), explosion proof indicating light for "low pressure" (amber), time delay relay for normal "door-open" condition, time delay relay for abnormal "low pressure" condition, remote alarm relay and explosion proof "off-purge-on" system switch.

The pressurization unit shall be a Model BFPD____ as manufactured by The Birdwell Company in Houston, Texas (no equal). Manufacturer reserves the right to change any product specifications without noticed.