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Air Quality

In the last century, California has changed to a hotter and dryer climate.  This coupled with the state's biome makeup which consists mainly of conifer, chaparral & oak woodlands has provided the optimal environment for a feedback loop that resulted in increasing severity, frequency, and extent of wildfires. Therefore, Californian's will have to be more cognizant of the Air Quality Index (AQI).

We advise our athletes that if the AQI is greater than 100  they do not train outdoors.

Athletes may train indoors if they have access to facilities with an appropriately sized and adequately filtered exterior air ventilation system.

How do you determine if a facility is safe for indoor training during high AQI?

  • The space should be supply ventilated, not exhaust ventilated or balanced. Energy Recovery & Heat Recovery Ventilator systems are adequate as well.

  • Ventilation should be filtered by a HEPA filter​ with a MERV rating of at least 13.

    • Non-Residential buildings that started construction in Q3 or Q4 of 2019 should meet this.

    • Buildings that have had their ventilation or HVAC systems completely replaced or had a completely new duct system installed in late 2019 will meet this as well.

  • The ventilation system should meet the recommended ACH for the space. 

Indoor Air Quality & Building Science

Wildfire smoke consists mostly of 0.4 - 0.7 micron-sized particles according to the Enivormental Protection Agency (EPA).

A High-Efficiency Particulate Air (HEPA) filter with Minimum Efficiency Reporting Values (MERVs) of 14 will capture 75+% of 0.3-1.0 micron-sized particles & 90+% of 1.0-3.0 micron-sized particles as determined by the American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE).

Ventilation is a key control strategy for providing good Indoor Air Quality (IAQ) in buildings. As it allows for fresh air to be replenished in the space and thereby lower indoor air pollutants such as carbon monoxide. The ASHRAE Standard 62.1 is incorporated into national, state, and local codes. Permit issue dates determine which code cycle buildings must adhere to. Title 24 the building energy code indicates the required minimum ventilation rate known as, Air Changes per Hour (ACH) which the conditioned space must meet. ACH is determined per person or per unit of floor area, based on the usage of the space in question.

ACH is a metric which indicates how many times the ventilation fills up the full volume of space it is serving with air. One can calculate it simply by taking the Cubic Feet per Minute (CFM) of airflow from the ventilation system multiplying that by 60 and dividing that by the volume of the conditioned space.

It is recommended that spaces such as Gyms have a 26 CFM/person ventilation rate as general guidance. Per 2019 Non-Residential Title 24 the minimum ventilation rate for a gym is 0.50 CFM/ft2 for the outdoor air rate and 0.15 is the minimum air rate.

IAQ is directly tied to how exterior air is brought into the conditioned space via ventialation. The US Department of Energy (DOE) has a good overview of the 4 different system configurations. There are ventilation systems that put air into the conditioned space, systems which suck air out and systems which treat the air before entering and leaving the conditioned space. Systems which such air out allow for outdoor air to leak into the conditioned space. Since the air entering the building in such systems can not be controlled it also can not be filtered. Systems where incoming exterior air is controlled can have air filtered before ventilation, such as in supply ventilation.


The above information on IAQ is a reflection of the relevant entities & local code and is not the opinion or stance of the school district.

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