IntroductionDisinfection & Sterilization Guidelines | CDC

Introduction to Indoor Air Quality | US EPA

Air Filtration

Filter Efficiency

  • Air filters should have a dust-spot rating between 35% and 80% or a Minimum Efficiency Rating Value (MERV) of between 8 and 13. The higher the rating, the better the protection for the equipment and the occupants. It has been estimated that a 30% increase in static pressure across a coil results in a $200 per 10,000 cfm of air movement (at 7 cents per KWH). This does not include the added cost of cleaning dirty heating or cooling oils, drain pans, or air ducts. Designers should consider specifying a low efficiency (~10%) pre-filter upstream of the main filters. The pre-filters are generally easy and inexpensive to change and will capture a significant amount of the particulate mass in the air thereby extending the useful life of the more expensive main filters.
    • See ASHRAE Standard 52.2-1999 Method of Testing General Ventilation Air Cleaning Devices for Removal Efficiency by Particle Size available at ASHRAE.

Pressure Drop

  • Design more filter surface area into ventilation systems. This has two advantages: the number of filter changes each year is reduced, thereby reducing the cost of labor to properly maintain the filters; and static pressure loss is lower, which saves money by reducing the amount of power needed to operate fans and blowers. Since different filter media are approximately proportional in their efficiency/pressure drop ratio, the most effective method for reducing pressure drop is to design more filter surface area into the filter system. This can be done by the specification of a filter with larger amounts of surface area, such as a pleated filter or bag filter. The next method is to increase the number and/or size of the filters in the airstream, for example, by mounting the filter slots in a “V” pattern, rather than a filter rack that is simply flat and perpendicular to the airstream.

Monitoring Pressure

  • Consider installing a simple pressure differential gauge across all filter banks. This will prevent school facilities personnel from having to guess whether the filter is ready for replacement. A gauge with a range of zero to 1.0 in. w.g. can save money and the environment by preventing premature disposal of filters that still have useful life and can prevent health and maintenance problems caused by overloaded filters that have blown out. The gauge should be easily visible from a standing position in an easily accessed location near the air handling unit.

Particulate Size (PM)

Particulate Matter (PM) Basics | US EPA

  • PM10 : inhalable particles, with diameters that are generally 10 micrometers and smaller; and
    PM2.5 : fine inhalable particles, with diameters that are generally 2.5 micrometers and smaller.
    How small is 2.5 micrometers? Think about a single hair from your head. The average human hair is about 70 micrometers in diameter – making it 30 times larger than the largest fine particle.
    Sources of PM
    These particles come in many sizes and shapes and can be made up of hundreds of different chemicals.
  • Some are emitted directly from a source, such as construction sites, unpaved roads, fields, smokestacks or fires.

What are the Harmful Effects of PM?

  • Particulate matter contains microscopic solids or liquid droplets that are so small that they can be inhaled and cause serious health problems. Some particles less than 10 micrometers in diameter can get deep into your lungs and some may even get into your bloodstream. Of these, particles less than 2.5 micrometers in diameter, also known as fine particles or PM2.5, pose the greatest risk to health.
  • Fine particles are also the main cause of reduced visibility (haze) in parts of the United States, including many of our treasured national parks and wilderness areas.
  • Learn more about health and environmental effects

What is Being Done to Reduce Particle Pollution?

  • EPA regulates inhalable particles. Particles of sand and large dust, which are larger than 10 micrometers, are not regulated by EPA.
  • EPA’s national and regional rules to reduce emissions of pollutants that form PM will help state and local governments meet the Agency’s national air quality standards. Learn about how air quality standards help reduce PM.
  • You can use air quality alerts to protect yourself and others when PM reaches harmful levels:
  • AirNow: Every day the Air Quality Index (AQI) tells you how clean or polluted your outdoor air is, along with associated health effects that may be of concern. The AQI translates air quality data into numbers and colors that help people understand when to take action to protect their health.
  • Go to About AirNow to learn how you can get AQI notifications.
    Also learn how the Air Quality Flag Program can help air agencies, schools, and other community organizations to notify their citizens of harmful conditions and adjust outdoor physical activities as needed.