Dilution ventilation
Used on the ASP and CSP. The worked example below is computed by code and checked against the source.
qd = (387 × lbs) ÷ (MW × min × d)
Qd = (qd × Km × 10^6) ÷ Ca
lbs = pounds evaporated; MW = molecular weight; min = minutes; d = density correction (1 at standard air); Km = mixing factor (2 to 5); Ca = acceptable concentration in ppm (typically half the PEL).
Worked example
2 lb of toluene (MW 92.14) evaporates in 60 min, d = 1, Km = 3, Ca = 50 ppm.
qd = 774 ÷ 5,528.4 = 0.140 cfm; Qd = 0.140 × 3 × 10^6 ÷ 50 = 8,400 cfm
Where it appears on the exam
ASP: ASP11 Domain 1, Mathematical Calculations
Blueprint: ASP11 Domain 1, task 3: flow rates (ventilation)
Practice: Ventilation Calculations
CSP: CSP11 Domain 6, Occupational Health and Applied Science
Blueprint: CSP11 Domain 6, task 1: occupational exposures (ventilation)
Practice: Applied Science: Radiation, Ventilation, Heat and Force
Source
The formula comes from
OSHA Technical Manual, Section III, Chapter 3 (Ventilation Investigation), General Exhaust (Dilution) Ventilation Systems(opens osha.gov in a new tab)“q d = [(387)(lbs)]/[(MW)(min)(d)] ... Q d = [(q d)(K m)(10 6)]/C a ... K m = mixing factor to account for poor or random mixing (NOTE: K m = 2 to 5; K m = 2 is optimum) C a = acceptable airborne concentration of the material (typically half of the PEL).”
Questions
- What is the formula for dilution ventilation?
- qd = (387 × lbs) ÷ (MW × min × d); Qd = (qd × Km × 10^6) ÷ Ca. lbs = pounds evaporated; MW = molecular weight; min = minutes; d = density correction (1 at standard air); Km = mixing factor (2 to 5); Ca = acceptable concentration in ppm (typically half the PEL).
- Will this formula be given on the BCSP exam?
- BCSP says the formula is included in the question whenever one is needed, unless the question is testing whether you know the formula. You can't bring a formula sheet into the exam, so learn what each formula does and when to use it.
BCSP on formulas at the exam
BCSP, What to Expect When Sitting for a BCSP Exam (item 7)(opens bcsp.org in a new tab)“For any question requiring a mathematical formula, the formula will be included within the exam question (unless the question is specifically testing your knowledge of a formula). You will not be provided or permitted to bring a formula sheet.”
Related
- 8-hour TWA exposure (air contaminants)
- Mixture of air contaminants
- Velocity from a smoke tube
- ASP formula sheet
- CSP formula sheet
Checked 2026-10-16. Spot a problem? Email hello@passcited.com.