© BLN, Inc. www.BowenEHS.com © BLN, Inc. www.BowenEHS.com © BLN, Inc. www.BowenEHS.com © BLN, Inc. www.BowenEHS.com © BLN, Inc. © BLN, Inc. Terms and Units Terms and Units Q’ = effective ventilation rate (cfm) Q = volumetric flow rate of air within ducts or into hood openings (cfm) Q = actual ventilation rate (cfm) K = safety factor, ranging from 1 to 10 ~ Used to calculate ventilation rates when employing dilution ventilation measures for low toxicity contaminants. © BLN, Inc. A = cross-sectional area of the duct or hood opening (ft2) V = average velocity of the air (fpm) ~ Commonly used equation industrial ventilation, normally used to find the third value when two variables are known. © BLN, Inc. © BLN, Inc. www.BowenEHS.com © BLN, Inc. www.BowenEHS.com © BLN, Inc. www.BowenEHS.com © BLN, Inc. www.BowenEHS.com Terms and Units Terms and Units V = average velocity of the air in a duct (fpm) TP = total pressure within a duct (inches of water) 4005 = constant based on the density of air (unit-less) VP = velocity pressure within a duct (inches of water) VP = average velocity pressure of air within a duct (inches of water) ~ Used to convert velocity pressure into velocity terms, based on a constant, 4005, which is based on the density of air. SP = static pressure within a duct (inches of water) ~ Used to calculate gauge pressures, referenced to atmospheric pressure. VP is always positive, SP and TP can be negative or positive. © BLN, Inc. © BLN, Inc. Terms and Units Terms and Units Ce = hood entry coefficient (unit-less) Q = volumetric flow rate (cfm) VP = duct velocity pressure (inches of water) he = hood entry energy loss measured as a fraction of the VP (inches of water) ~ Used to calculate hood entry loss factor, or energy loss, for air entering a hood. © BLN, Inc. A = area of the duct (ft2) 4005 = constant SP = hood static pressure (inches of water) Ce = hood entry coefficient (unit-less) ~ Used as a measure of hood performance, also called the throat-suction equation. © BLN, Inc. © BLN, Inc. www.BowenEHS.com © BLN, Inc. www.BowenEHS.com © BLN, Inc. www.BowenEHS.com © BLN, Inc. www.BowenEHS.com Terms and Units Terms and Units C = airborne concentration of a gas or vapor (ppm) Ce = hood entry coefficient (unit-less) G = generation rate of a gas or vapor (cfm) VP = velocity pressure (inches of water) Q’ = effective dilution volumetric flow rate (cfm) N = number of room air changes per hour (ACH) 60 = factor to convert minutes to hours e = natural logarithm (2.718) 106 = factor to convert the answer to ppm ~ Used to calculate concentration buildup when initial concentration is zero. t = time interval (minutes) ISPhI = absolute value of the hood static pressure (inches of water) ~ The coefficient of entry uses the ratio of kinetic to potential pressures to measure the efficiency of a ventilation system. © BLN, Inc. © BLN, Inc. Terms and Units Terms and Units SPfan = fan static pressure (inches of water) ISPhI = absolute value of the hood static pressure (inches of water) SPout = static pressure on the outlet side of the fan (inches of water) SPin = static pressure on the inlet side of the fan (inches of water) VPin = velocity pressure on the inlet side of the fan (inches of water) ~ Used to calculate the fan static pressure, a variable used in measuring ventilation system performance. © BLN, Inc. VP = velocity pressure within a duct (inches of water) he = hood entry loss measured as a fraction of the VP (inches of water) ~ Used to calculate the energy needed to accelerate room air to duct velocity, taking into account the turbulence losses around the hood opening. © BLN, Inc. © BLN, Inc. www.BowenEHS.com © BLN, Inc. www.BowenEHS.com © BLN, Inc. www.BowenEHS.com © BLN, Inc. www.BowenEHS.com Terms and Units Terms and Units 403 = constant, SG = specific gravity (unit-less) Q = effective dilution ventilation rate (cfm) Q = volumetric flow rate of dilution air (cfh) G = generation rate of a gas or vapor (cfm) MW = molecular weight of contaminant (g) TLV = acceptable airborne concentration of a gas or vapor (ppm) 106 = conversion factor to allow TLV to be in ppm 106 = a conversion factor to allow TLV to be in ppm ~ Used to calculate the amount of dilution air required to keep airborne concentraion of low toxicity materials at an acceptable level, taking into account the vapor generation rate. ER = evaporation rate of contaminant (pt/hr) K = dilution ventilation safety factor (unit-less; 3-10) C = Threshold Limit Value® or acceptable air concentration (ppm) ~ Used to calculate the amount of dilution air required to keep airborne concentraion of low toxicity materials at an acceptable level, taking into account the specific gravity of the solvent, under steady state conditions. © BLN, Inc. © BLN, Inc. Terms and Units Terms and Units V = the capture velocity at distance X (fpm) C = airborne concentration (ppm) Pv = vapor pressure of contaminant at a certain temperature (mmHg) Q = the airflow through the system (cfm) 10 = a constant Pb = barometric (atmospheric) pressure (mmHg) x = the centerline distance to the hood opening (ft) A = the area of the hood opening (ft2) ~ Used to calculate the volumetric flow rate necessary to control a vapor at a certain distance from a plain hood opening. © BLN, Inc. 106 = conversion factor to express C in terms of ppm ~ Used to calculate the equilibrium (saturation) concentration of a gas or vapor, based on the vapor pressure and atmospheric pressure. © BLN, Inc. © BLN, Inc. www.BowenEHS.com © BLN, Inc. www.BowenEHS.com © BLN, Inc. www.BowenEHS.com © BLN, Inc. www.BowenEHS.com Terms and Units Terms and Units ln = natural logarithm V = room volume (ft3) G = generation rate of a gas or vapor (cfm) ln = natural logarithm Q’ = effective flow rate of dilution air (cfm) G = generation rate of a gas or vapor (cfm) t1, 2 = initial and final times when C1, 2 are reached (minutes) Q’ = effective flow rate of dilution air (cfm) V = room volume (ft3) C1, 2 = initial and final airborne concentrations of a contaminant in the decimal equivalent of parts per million (ppm/106) C1, 2 = initial and final airborne concentrations of a contaminant in the decimal equivalent of parts per million (ppm/106) ~ Used to calculate the time needed to purge room concentration of an airborne contaminant once active generation has ceased. t = timed interval when C is reached (minutes) ~ Used to find the concentration of a gas or vapor after a period of time, or to find the effective ventilation flow rate. © BLN, Inc. © BLN, Inc. © BLN, Inc. © BLN, Inc.
