Optimal comfort: hygiene and healthy contaminant levels

Achieving optimal comfort in your home or workplace involves obtaining high air quality within these spaces. Do you know what the healthy levels of contaminants in the air are? Below, we will review the current legislation in terms of indoor air quality and point out the legally established concentration levels in the air for certain contaminant components.

Indoor air quality for optimal comfort: a regulatory obligation

According to NTP 243 Closed Environments: air quality, from the Ministry of Labor and Social Affairs, since 2013 it has been mandatory to inspect air quality to achieve optimal comfort. Thus, it is necessary to carry out an annual review of the ductwork and the environmental quality for thermal installations in buildings whose useful power is equal to or greater than 70 kW (both in cooling and heating). While individual dwellings are exempt from meeting this requirement, the vast majority of other buildings must comply.

Do you know how many types of contaminants we are exposed to?

There are different sources from which the various types of contaminants present in the air can arise:

• Humans. Since people naturally produce CO₂, water vapor, particles, and biological aerosols, it can be said that the occupants of a building are themselves a source of pollution.
• The building itself and its contents.
• Combustion processes that occur inside buildings.
• Chemical products used in cleaning and maintenance.

Some of these sources produce complex mixtures such as tobacco smoke, aerosols, and fumes generated by food preparation, infectious biological aerosols, and allergens generated in cooling circuits.

Guides and allowable average concentrations

Many organizations have developed exposure guides and standards (WHO, CIBC, and ASHRAE, among others). All of them emphasize the need to refresh air in closed environments, providing a minimum supply of fresh air per occupant that dilutes the concentrations of human bioeffluents and thus prevents discomfort that bad odors can cause.

In the 1970s, ASHRAE published various studies recommending a minimum supply of fresh air of 34 m³/h per person to avoid bad odors and an absolute minimum of 8.5 m³/h per person to keep CO₂ concentrations below 2500 ppm (for optimal comfort, they recommend a maximum CO₂ concentration of 1000 ppm). In its most recent study, ASHRAE Standard 62-1989, it recommends a minimum of 25.5 m³/h per person for school classrooms, 34 m³/h for offices, and 42.5 m³/h for hospitals (in the patient area). This standard recommends increasing these volumes if there are air mixing problems in the breathing zone or unusual sources of pollution. Without forgetting that a good level of thermal comfort must be achieved in enclosed spaces, it states that the indoor temperature should be maintained between 20 and 24 °C in winter and between 23 and 26 °C in summer. Although this standard does not specify it, it is considered that relative humidity should be between 20 and 60% (preferably between 30 and 50%).

According to the General Ordinance of Safety and Hygiene in the Workplace, the values must be as follows:

• Air supply:
  • 30 - 50 m³/h per employee, or a total air renewal of 6 times/hour for sedentary work and 10 times/hour for physically demanding work.
• Air velocity
  • 15 m/min (normal temperature) and 45 m/min (hot environment)
• Temperature
  • 17 to 22 °C (sedentary work)
  • 15 to 18 °C (ordinary work)
  • 12 to 15 °C (work that requires significant physical effort)
• Relative humidity
  • 40 - 60%
  • >50% if static electricity can be generated.