OHE Flashcards
Rate Generation of Air Contaminant
Ln((G -QC) / G) =(Qt/V)
C = G/Q(1-e^(-Qt/V))
Ln (C(2)/C(1)) = (-Q/V) * (t(2) - t(1))
G: generation rate
Q: ventilation rate
C: concentration after t minutes
V: volume in ft^3 t: time in minutes
Note: If C’s given in ppm, divide by 10^6 before using formulae. If calculating C, multiply by 10^6.
General Ventilation Air Flow Rate
Q = (403 * SG * 10^6 * P * K) / (MW * L) Q: req’d airflow, ft^3/hr SG: specific gravity P: # pints evaporated per hour K: safety factor MW: molecular weight L: max concentration allowed, eg LFL or TLV in ppm
Sound Transmission Loss Materials
STL = 10 log (E(i)/E(t)) E(i): incident energy E(t): transmitted energy STL increases w increasing frequency, 5dB for each doubling of frequency.
Noise Reduction of a Duct
NR = (12.6 * P * alpha ^ 1.4) / A NR: Noise reduction, dB/ft P: duct perimeter, inches alpha: absorption coefficient of lining material A: duct cross sectional area, sq in
Intensity, decay, initial activity
I = I(0) * e^-(μ * x) I: activity after time x I(0): initial activity μ: decay constant or coefficient Note: Many decay values are in sec^-1! So when solving for x I may need to * intermediate value by 10^-1!
Hood Capture Velocity at a Distance
V = Q / (10x^2 + A) V: capture velocity (fpm) at distance x from hood Q: volumetric flow rate (cfm) x: centerline distance from hood opening (ft) A: hood opening area (ft^2)
Sound Pressure Level & Distance
dB(1) = dB(0) + 20 * log (d(0) / d(1))
Coefficient of Entry for a Hood
C(e) = sqrt(VP/SP(h)) C(e): coefficient of entry VP: velocity pressure SP(h): static pressure of the hood
Air Velocity, Entry Coefficient, & Static Pressure
V = 4,005 * C(e) * sqrt(SP(h)) V: air velocity, fpm C(e): hood entry coefficient SP(h): hood static pressure, in. wg.
Dilution Ventilation Rate for Given Generation Rate and TLV
Q = 10^6 * (G/TLV) Q: dilution rate, cfm G: generation rate, cfm TLV: ppm
Activity of a Radioactive Isotope
A = A(0) / e^[ln 2 (t / t(1/2))] t(1/2): half-life t: time (days) since A(0) was measured Note: ln2/t(1/2) often appears as lambda, the decay constant
Rate of Dilution Ventilation of a Given Volume
Ln(C(2)/C(1)) = (-Q/V) * (t(2) - t(1)) C: concentration Q: air flow rate, ft^3/min V: volume, ft^3 t: time, min
Radiation Attenuation Shielding with Buildup
I(1) =I(0) * b * e^−μx
I(1) = the shielded dose rate I(0) = the initial dose rate
b: buildup factor
μ = the linear attenuation coefficient in –cm
x = the shield thickness in cm
Fans & Pressures
SP(fan) = SP(out) - SP(in) - VP(in)
Remember that the inlet side is low pressure, and therefore even if its pressures aren’t always written as negative values, they are! So in practice one usually ends up adding the absolute value of SP(in).
