CIH Questions
1. What is the flow (Q) of an 4-inch diameter duct with a 50 feet per minute (ft/min) duct velocity?
(Answer to the nearest hundredths place) (#.##) []
a. 9.81 ft3/min or fpm
2. An Industrial hygienist measures the circumference of a duct to be 32 inches, and the velometer
registers a value of 100 feet per minute (ft/min). What is the flow (Q)? (Round to the nearest
tenths place) (#.#) [] ft3/min
a. 54.5 ft3/min
3. The duct area of an 6-inch diameter duct with a 100 feet per minute duct velocity is reduced to
a 3-inch diameter duct. What is the new velocity? Whole number []
a. 400 fpm (flow increases 4 times)
4. What is the total pressure (TP) in a duct pre fan if static pressure (SP) is -2.0 in. wc. and velocity
pressure (VP) is .75 in. wc. (Round to the nearest hundredths place) (#.##) []
a. TP=-1.25
5. One measurement at the entry point of a section of ductwork has a total pressure of 2.75 in.
wc., and 1.25 in. wc. at the exit point. What is the head (energy) loss across the ductwork?
(Round to the nearest tenths place) (#.#) []
a. 1.5 in.wc.
6. Calculate the hood static pressure if the duct velocity pressure (VPd) is 0.4 in. wc. and the hood
entry loss factor (Fh) is 0.25. (Round to the nearest tenths place) (#.#) []
a. -0.5 in. wc
7. The velocity pressure (VP) in a duct is 3.5 in. wc. What is the velocity (V) if the density factor is 1
(at 70 °F and 14.7 psi)? Whole number []
a. 7493 fpm
8. The velocity pressure (VP) in a duct is 2.0 in. wc. What is the velocity (V) if the density factor
must be corrected for 100 0C and 14.5 psi? Whole number []
a. 8495 fpm
9. The velocity in a duct is 8,525.5 fpm. What is the velocity pressure if the density factor is 2?
(Round to the nearest hundredths place) (#.##) []
a. 9.06 in.wc.
10. The velocity in a duct is 18.24 m/sec. What is the velocity pressure at standard temperature and
pressure? Whole number []
a. 200 Pa
11. What is the hood entry loss if the hood entry loss factor is 0.80 and the velocity pressure in the
duct is 0.40 in. wc.? (Round to the nearest hundredths place) (#.##) []
a. 0.32 in.wc.
12. Determine the coefficient of entry for a hood within a duct with a velocity pressure of 0.5 in. wc.
and a hood static pressure of 0.7 in. wc. (Round to the nearest hundredths place) (#.##) []
a. 0.85
13. What is the resulting velocity pressure in a duct resulting from two merged flow ducts, first with
a volumetric flow rate of the duct of 150 ft3/min and 1.5 in. wc. and the second with a
volumetric flow rate of the duct of 200 ft3/min and 2.0 in. wc.? (Round to the nearest
hundredths place) (#.##) []
a. 1.56 in.wc.
14. Calculate the volumetric flow rate (Q) of a 12-inch diameter (A = 0.7854ft2) duct from a hood, if
the hood static pressure measurement is 2.25 in. wc. also, the hood entry coefficient is 0.98
(bell-shaped) with a density factor of 1. Whole number []
a. 4,624 ft3/min
15. Calculate the volumetric flow rate in fpm of a 8-inch diameter, 1 inch = 2.54 cm (A = 0.4064 m2)
duct from a hood, if the hood static pressure measurement is 524.7 Pa and the hood entry
coefficient is 0.98 (bell-shaped) with density factor 1, and the conversion factor m3 to ft3 is
35.28. Whole number []
a. 1,962 ft3/min
16. : Calculate the volumetric flow rate (Q) of a 8-inch diameter duct (A = 0.196 ft2) from a hood, if
the hood static pressure measurement is 1.75 in. wc. and the hood entry coefficient is 0.98 (bellshaped). Whole number []
a. 1,018 ft3/min
17. Calculate the corrected flow for a ventilation branch converging the main duct with a static
pressure of 1.8 in. wc. The joining ventilation branch has a volumetric flow rate of 2000 ft3/min
and static pressure of 1.6 in. wc. Whole number []
18.
19.
20.
21.
22.
a. 2121 ft3/min
What is the effective rate of ventilation in a room if the rate of ventilation is 40 ft3/min, and the
mixing factor is 10? Whole number []
a. 4 ft3/min
: Benzene spills in a room that measures 35’ x 35’ x 35’ (42875 ft3). An initial concentration is
measured at 35 ppm, and the benzene use is stopped (no more benzene vapors are released).
With the effective rate of ventilation 3,500 ft3/min of dilution air, how long would it take to
reach the PEL level of 1 ppm? (Round to the nearest hundredths place) (#.##) []
a. 43.55 min
Benzene evaporates at a rate of 5 ft3/min in a room that measures 45’ x 60’ x 20’ (54,000 ft3). If
an initial concentration measured is 55 ppm, what will the concentration be after 50 minutes of
5,500 ft3/min of dilution air at? []
a. C2 = 0.000999475 ≌ 1000 ppm
Benzene evaporates from an open bottle that must remain open on a laboratory table at a rate
of 0.1 pints/min. How many ft3/min dilution air is required to maintain the concentration below
the PEL? Assume the PEL is 1 ppm and a ventilation safety factor of 2. The molecular weight is
78.11 g/mol, and the specific gravity is 0.876. Whole number []
a. 1,506,542 ft3/min
b. Equation I used
i. (403*0.876*0.25*2*10^(6))/(78.11*1.5) is the 1.5 value wrong?
Benzene evaporates from an open bottle that must remain open on a laboratory table at a rate
of 0.00093 liters/second. How many ft3/min dilution air is required to maintain the
concentration below the PEL? Assume the PEL is 1 ppm and a ventilation safety factor of 2. The
molecular weight is 78.11 g/mol, the specific gravity is 0.876, and the conversion factor m3 to
ft3 is 35.28. Whole number []
a. 1,060,787 ft3/min
23. : A room measures 35 x 35 x 12 feet (14700 ft3). How many air changes per hour are done using
a ventilation rate of 3500 ft3/min? Whole number []
a. 14 air changes per hour
24. A room measures 25 x 25 x 15 feet (9375 ft3) and has a ventilation rate of 2750 ft3/min.
Benzene evaporates from an open bottle left on a laboratory table at a rate of 0.1 ft3/min. What
is the final concentration of benzene after 15 min? (#.####_) []
a. 0.00004 ppm
25. A room measures 20 x 30 x 25 feet (15000 ft3) and has a ventilation rate of 3000 ft3/min.
Benzene evaporated from an open bottle left on a laboratory table and reached 60 ppm
concentration before closing the bottle with a rubber stopper. What is the final concentration of
benzene after 30 min? (Round to the nearest hundredths place) (#.##) []
a. 30min: 0.15 ppm
26. A local exhaust ventilation system with a flow of 500 ft3/min has its fan turning at 6000 rpm
replaced by a 5000 rpm. If the fan diameter remains the same, what is the new flow? Whole
number []
a. 600 ft3/min
27. A local exhaust ventilation system with a fan pressure 2 of in. wc. has its fan turning at 2500 rpm
replaced by a 3500 rpm. If the fan diameter remains the same, what is the new flow? (Round to
the nearest hundredths place) (#.##) []
a. 3.92 in. wc.
28. To improve the local exhaust ventilation of a 30-horsepower fan turning at 5000 rpm the fan
speed is increased by 20%, what is the new horsepower of the fan? Whole number []
a. 65 hp
29. What is the fan static pressure (FSP) when the static pressure at the inlet (SPin) is -3.5 in. wc. the
static pressure at the outlet (SPout) is 6 in. wc. and the velocity pressure on the inlet side of the
fan (VPin) is 1.5 in. wc.? Whole number []
a. 8 in. wc.
30. What is the fan total pressure (FTP) when the total pressure at the inlet (TPin) is – 5.0 in. wc. the
total pressure at the outlet (TPout) is 5 in. wc.? Whole number []
a. 10 in. wc.