MRS HEPA Filtration & Air Scrubbing 3 — Questions and Answers
Question 1: A HEPA filter must capture what minimum percentage of particles at 0.3 microns to meet the HEPA standard?
- 95.0%
- 97.5%
- 99.97% (Correct answer)
- 99.999%
Correct answer: 99.97%
True HEPA filters must capture at least 99.97% of airborne particles at the most penetrating particle size of 0.3 microns.
Question 2: During mold remediation, HEPA-filtered vacuums should be used instead of standard shop vacuums because:
- Standard vacuums generate static electricity that attracts mold
- Standard vacuums exhaust mold spores back into the air (Correct answer)
- Standard vacuums are too loud for indoor use
- Standard vacuums cannot handle wet debris
Correct answer: Standard vacuums exhaust mold spores back into the air
Standard shop vacuums lack HEPA filtration and their exhaust air disperses fine mold spores throughout the environment, worsening contamination.
Question 3: When sizing a negative air machine for a containment, the cubic feet per minute (CFM) rating should be calculated based on:
- The square footage of the floor area only
- The total cubic footage of the containment space and desired ACH (Correct answer)
- The number of workers in the containment
- The moisture content of the affected materials
Correct answer: The total cubic footage of the containment space and desired ACH
CFM requirements are determined by multiplying the containment volume (cubic feet) by the desired air changes per hour, then dividing by 60 minutes.
Question 4: Which condition would most likely cause a HEPA air scrubber to lose effectiveness during operation?
- Running the unit continuously for more than 4 hours
- Operating the unit in high humidity above 60% RH
- A clogged or overloaded HEPA filter restricting airflow (Correct answer)
- Positioning the unit in the center of the containment
Correct answer: A clogged or overloaded HEPA filter restricting airflow
A clogged HEPA filter dramatically reduces airflow (CFM), cutting the number of air changes per hour and allowing contaminants to remain airborne longer.
Question 5: In mold remediation, 'air washing' refers to:
- Using water mist to suppress airborne spores
- Continuously filtering the air in a space to reduce airborne contaminant levels (Correct answer)
- Spraying antifungal solutions through the HVAC system
- Pressurizing the containment to push spores into filters
Correct answer: Continuously filtering the air in a space to reduce airborne contaminant levels
Air washing is the process of continuously recirculating and filtering air through HEPA equipment to progressively reduce airborne contaminant concentrations.
Question 6: What tool is used to verify that a negative air machine is maintaining adequate pressure differential in a containment?
- Hygrometer
- Manometer or magnehelic gauge (Correct answer)
- Particle counter
- Infrared thermometer
Correct answer: Manometer or magnehelic gauge
A manometer or magnehelic gauge measures the pressure differential (in inches of water column) between the containment interior and the surrounding area.
Question 7: After mold remediation work is complete, the air scrubber should be run for an additional period primarily to:
- Dry out residual moisture in the containment
- Reduce airborne particle levels before clearance testing (Correct answer)
- Cool down the motor before transport
- Eliminate any chemical odors from cleaning agents
Correct answer: Reduce airborne particle levels before clearance testing
Running the air scrubber after work is complete allows additional air changes to settle and capture disturbed spores before clearance air sampling is performed.
MRS HEPA Filtration & Air Scrubbing 3
A HEPA filter must capture what minimum percentage of particles at 0.3 microns to meet the HEPA standard?