Ventilation Calculations questions for the ASP
ASP11 Domain 1: Mathematical Calculations (1.x Ventilation (flow, velocity, dilution)). 3 free questions below. Every answer quotes and links the formula source it rests on.
Question 1Calculation
To check a laboratory hood, a technician releases a puff of smoke at the face and times it traveling 2 feet into the hood in 1.5 seconds. The hood face opening is 2.5 ft wide by 2 ft high. What is the approximate airflow (Q) into the hood?
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Answer: C. 400 cfm
V = D/T = 2 ft / 1.5 s = 1.33 ft/s = 80 fpm. Flow is velocity times area (velocity = flow / area): Q = 80 fpm x 5 ft² = 400 cfm. Forgetting to convert seconds to minutes gives a value 60 times too small.
Answer C rests on
OSHA Technical Manual, Section III, Chapter 3 (Ventilation Investigation), IV.F.3.d and Appendix III:3-2(opens ecfr.gov in a new tab)“Velocity = Distance/Time, or V = D/T Squeeze off a quick burst of smoke. Time the smoke plume's travel over a two-foot distance. Calculate the velocity in feet per minute. For example, if it takes two seconds for the smoke to travel two feet, the velocity is 60 fpm. ... Slot velocity is calculated by dividing the total volume flow rate by the slot area”
Question 2Calculation
To check a laboratory hood, a technician releases a puff of smoke at the face and times it traveling 2 feet into the hood in 2.5 seconds. The hood face opening is 2 ft wide by 2 ft high. What is the approximate airflow (Q) into the hood?
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Answer: B. 192 cfm
V = D/T = 2 ft / 2.5 s = 0.80 ft/s = 48 fpm. Flow is velocity times area (velocity = flow / area): Q = 48 fpm x 4 ft² = 192 cfm. Forgetting to convert seconds to minutes gives a value 60 times too small.
Answer B rests on
OSHA Technical Manual, Section III, Chapter 3 (Ventilation Investigation), IV.F.3.d and Appendix III:3-2(opens ecfr.gov in a new tab)“Velocity = Distance/Time, or V = D/T Squeeze off a quick burst of smoke. Time the smoke plume's travel over a two-foot distance. Calculate the velocity in feet per minute. For example, if it takes two seconds for the smoke to travel two feet, the velocity is 60 fpm. ... Slot velocity is calculated by dividing the total volume flow rate by the slot area”
Question 3Calculation
To check a laboratory hood, a technician releases a puff of smoke at the face and times it traveling 2 feet into the hood in 1 seconds. The hood face opening is 4 ft wide by 2 ft high. What is the approximate airflow (Q) into the hood?
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Answer: A. 960 cfm
V = D/T = 2 ft / 1 s = 2.00 ft/s = 120 fpm. Flow is velocity times area (velocity = flow / area): Q = 120 fpm x 8 ft² = 960 cfm. Forgetting to convert seconds to minutes gives a value 60 times too small.
Answer A rests on
OSHA Technical Manual, Section III, Chapter 3 (Ventilation Investigation), IV.F.3.d and Appendix III:3-2(opens ecfr.gov in a new tab)“Velocity = Distance/Time, or V = D/T Squeeze off a quick burst of smoke. Time the smoke plume's travel over a two-foot distance. Calculate the velocity in feet per minute. For example, if it takes two seconds for the smoke to travel two feet, the velocity is 60 fpm. ... Slot velocity is calculated by dividing the total volume flow rate by the slot area”
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