SECTION 297.8. Guidelines for Comfort and Minimum Risk Levels

(a) IAQ Comfort. Comfort is an important part of indoor air quality. The major comfort issue is thermal comfort that involves temperature, relative humidity, and air velocity. Other comfort issues not covered here but that could affect the indoor environment are lighting, noise, and vibration. Maintaining the proper temperature range is not sufficient to achieve thermal comfort; it is also necessary to properly control the combination of temperature, relative humidity and air velocity.

(1) Temperature. The room temperature for a typical occupied office or classroom environment should be kept between 72 to 76 degrees Fahrenheit in the summer and 70 to 75 degrees in Fahrenheit in the winter and controlled within a temperature range of ±2 degrees in Fahrenheit for a given day. Temperature at body and head height and near the floor needs to be considered. Occupant preferences, activity and attire will influence the comfort. Additional guidance documents for other situations are available, including ASHRAE Standard 55-1992 and 55a-1995.

(2) Relative Humidity. The relative humidity for a typical occupied office or classroom environment should be generally between 30 to 50%. The relative humidity should never exceed 60% due to potential mold growth. In geographical regions where the outdoor relative humidity is typically below 30%, no humidification is recommended if the occupants do not complain of discomfort due to the dryness.

(3) Air Velocity. Some air movement is recommended to avoid a feeling of stagnant air, typically 25 to 55 feet per min (fpm). Higher air speeds may be acceptable if the affected occupants have control of local air speeds. Air supplied to the occupied zone (standing and sitting positions) should be supplied at a moderate velocity within the recommended temperature and relative humidity ranges. Air supplied from a diffuser at elevated speeds can create drafts in the occupied zone, causing complaints of too hot or too cold, dry eyes, sore throats and nasal irritation. Directing diffusers directly onto occupants' work zones or directly overhead may cause occupants discomfort, resulting in them "modifying" the supply system (e.g., placing cardboard over diffusers). The system should be properly tested and balanced. The appropriate supply and exhaust diffusers based on the occupant locations should be installed. These diffusers should supply air at an acceptable temperature and humidity. Additional guidance documents are available, including ASHRAE Standard 55-1992 and 55a-1995.

(b) Minimum Risk Levels. Table 1 in paragraph (4) of this subsection provides Minimum Risk Levels (MRLs) for common contaminants found in indoor air. The MRLs in Table 1 are not IAQ standards. There are no required federal or Texas standards for indoor air contaminants. The MRLs are based on the data contained in the Texas Commission on Environmental Quality's (formerly the Texas Natural Resources Conservation Commission) Effects Screening Levels List (July 19, 2000), the Agency for Toxic Substances and Disease Registry's (ATSDR) Minimal Risk Levels for Hazardous Substances (December 2001), and the Environmental Protection Agency's (EPA) Integrated Risk Information System (IRIS) inhalation RfC values and the National Primary and Secondary Air Quality Standards (40 CFR 50). These information sources can be used as a reference for other contaminants not listed in Table 1.

(1) These levels are based on inhalation for an eight hour exposure for the general public. If a particular contaminant is expected to last significantly longer, the MRL should be lowered to compensate for the longer duration. The references in subsection (b) of this section may have this information. For one year, a reasonable approximation is to multiply the 8-hour MRL by 0.14.

(2) Most of the MRLs are at a no-observed-adverse-effect-level. They are set below levels that, based on current information, might cause adverse health effects in the people most sensitive to such substance-induced effects. If the indoor levels of contaminants in air exceed the MRL, it does not necessarily indicate a problem, but should trigger a concern for a more in-depth evaluation of the potential health effects or to reduce the concentration below the MRL. Most of the MRLs are based on non-cancer health effects only.

(3) The MRLs are expressed in units of parts per million (ppm) for most gases and volatiles, or milligrams per cubic meter (mg/m ³ ) for particles and some volatile organic compounds (VOCs).

(4) Table I. Common Indoor Air Conditions/Contaminants in Government Buildings.

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Source Note: The provisions of this §297.8 adopted to be effective December 22, 2002, 27 TexReg 11759