3003 W CASINO RD BLDG 40-23 2018-01-02 MF Import

May 24, 1994 4-3212-4-328 To cc Subject: Reference: LtO - ,13 ) M. Gosnold L. Astemborski Van Tassel Hayes Burns C,AS�tit, yo a- y OH-13 OH-13 OF-10 OM-31 OH-06 Buildings 40-23 and 40-24, Everett Hazardous Classification of Chemical Crib Fume Hood Fans (a) Evaluation of the chemical crib exhaust fans used for the dispensing fume hoods within the cribs (b) Memo dated May 24, 1994, F. Ford (Greenheck Cube Fans) to S. Lusk (Austin Co.), regarding the type of motor used for the chemical crib exhaust fan fume hoods Fire Protection Engineering has reviewed the reference (a) issue. The fume hoods are used to dispense methyl ethyl ketone (MEK) from 5-gallon safety cans into one pint squeeze bottles. Normally, the dispensing of MEK is done from a single 5-gallon can at a time. The fume hood has exhaust ventilation to the atmosphere via a 3000 cfm exhaust fan. A separate and independent low level exhaust system exists for the chemical crib itself. The crib is a "B-2" non -hazardous occupancy as defined in Chapter 7 of the 1991 Uniform Building Code (UBC). The crib low level exhaust ventilation system complies with that required by section 705(b) of the UBC in areas where Class Ib flammable liquids (ie. MEK) are dispensed. The separate exhaust system for the fume hood was not required by the UBC. It was installed to eliminate the fumes during the dispensing of the MEK and thereby creating a more comfortable environment for the crib attendant. A safety ventilation calculation done using the properties of MEK indicates that one gallon of liquid MEK will produce 35.5 ft. /gal. of MEK vapor at an ambient temperature of 70'F. The volume of air needed to render the leanest explosive mixture at the lower explosive limit (LEL-1.7) of MEK is 2056 ft. per gallon of MEK. This means that for every gallon of MEK liberated during dispensing, 2056 ft. of air is needed to create an explosive mixture at the L3FL. A chemical crib that dispenses 10 gallons an hour would need 20,560 ft. of air per hour (343 cfm) to render an explosive mixture at the LEL. A fresh air volume of 1372 cfm (343 cfm X 4) would create a mixture at 25% of the LEL. The crib exhaust fan is rated at 3000 cfm. This reduces the actual mixture of air being exhausted to 11% of the LEL. Please note that if dispensing of MEK takes place without the fume hood on, the room low level exhaust system will exhaust the MEK fumes since MEK is heavier than air. The room exhaust system runs continuously irregardless if dispensing of MEK is taking place.