Indoor air quality

Pollutants, sources and effects

The air in a building receives pollutants from occupants (carbon dioxide, bioeffluents, biological agents), materials and furnishings (volatile organic compounds, formaldehyde), activities (cleaning products, printers and photocopiers, cooking), systems (humidity, dirty ducts and filters, cooling towers and humidifiers containing Legionella, incomplete combustion producing carbon monoxide), and from the outside (traffic, pollen, particulate matter, radon from the ground). Insufficient ventilation, poor air conditioning maintenance, and unsuitable temperatures and humidity levels exacerbate the problem.

Common effects include irritation of the eyes, nose, and throat, headache, fatigue, difficulty concentrating, dry skin and mucous membranes, and respiratory and allergic symptoms. When a significant proportion of occupants experience these symptoms, which improve upon leaving the building, without a single identified cause, it is referred to as sick building syndrome, described in INSST Technical Notes 289 and 290. Other building-related illnesses, with known diagnoses and causative agents, include Legionnaires’ disease, hypersensitivity pneumonitis, occupational asthma, and carbon monoxide poisoning.

Royal Decree 486/1997 establishes in Annex III the environmental conditions for workplaces: a temperature between 17 and 27 degrees Celsius for sedentary work and between 14 and 25 degrees Celsius for light work, relative humidity between 30 and 70 percent (50 percent minimum if there is a risk of static electricity), and a minimum air renewal rate of 30 cubic meters of clean air per hour per worker for sedentary work in non-hot and non-polluted environments, and 50 cubic meters per hour in other cases, in order to prevent stale air and unpleasant odors. The Regulation on Thermal Installations in Buildings classifies the required indoor air quality (IDA 1 to IDA 4) according to the building’s use and sets ventilation, filtration, and maintenance flow rates.

Parameters, evaluation and measures

• Carbon dioxide. An indicator of air renewal relative to occupancy; concentrations above 1,000 parts per million usually indicate insufficient ventilation, although it is not a toxic pollutant at those levels.
• Temperature and humidity. Thermal comfort parameters and biological proliferation control; NTP 243 and UNE-EN 16798-1 provide design and evaluation criteria.
• Volatile organic compounds and formaldehyde. Originating from materials, furniture, paints, adhesives, and cleaning products; they are reduced by selecting low-emission materials, ventilation after construction work, and product control.
• Particles and ozone. Originating from outside, from printers and equipment and from indoor activities; they are controlled with adequate filtration, maintenance and equipment location.
• Biological agents. Fungi and bacteria in damp areas, ducts, filters and humidifiers; legionella in cooling towers, evaporative condensers, domestic hot water and other systems regulated by Royal Decree 487/2022.
• Carbon monoxide and radon. Serious risks: faulty combustion and connected garages, and radon in areas of geological risk, with obligations under Royal Decree 1029/2022 on protection against ionising radiation .
• Evaluation. Analysis of complaints and symptoms (NTP 380), inspection of the facilities and the building, measurements of basic parameters and, if applicable, of specific contaminants, in accordance with NTP 243 and 431.
• Measures. Act on the sources (materials, products, activities), ensure ventilation and its distribution, maintain the facilities, control temperature and humidity, and manage complaints systematically.

Facilities, maintenance and responsibilities

• Ventilation and air conditioning. Outdoor air flow rates compliant with RITE and Royal Decree 486/1997, distribution that avoids dead zones and short circuits, air intakes away from sources of contamination and control of recirculation.
• Maintenance. Inspection and cleaning of ducts, filters, air handling units, condensate trays and humidifiers in accordance with the RITE maintenance program and UNE 171330, with records.
• Legionella. Hygiene and sanitation maintenance program for at-risk facilities, including cleaning, disinfection, analysis and records in accordance with Royal Decree 487/2022.
• Construction and renovation. Ventilation and insulation of areas during construction, selection of low-emission materials and ventilation period before occupancy.
• Teleworking and third-party buildings. Law 10/2021 and the coordination of business activities extend attention to spaces where staff work outside of company premises.
• Participation. Consulting with workers and their representatives and providing a channel for communicating complaints facilitate the early detection of problems.

Organizational application: how to manage indoor air quality

1. Inventory the buildings and workspaces with their ventilation and air conditioning systems, legionella risk facilities and radon risk areas.
2. Include indoor air quality in the risk assessment of office and public service positions, with basic parameters (temperature, humidity, carbon dioxide) and review of pollution sources.
3. Establish the facility maintenance program in accordance with the RITE and Royal Decree 487/2022, with records of cleaning, filter replacement, disinfection and analysis.
4. Implement a channel for communicating complaints and symptoms and an investigation procedure (survey, inspection, measurements) when they accumulate.
5. Control cleaning products, construction and renovation materials, and the location of emitting equipment.
6. Inform the occupants about the environmental conditions and the measures taken, and consult with the workers’ representatives.
7. Periodically review the conditions with measurements and audits of the air conditioning system, and after changes in occupancy or layout.

Preventive management software allows you to record environmental measurements by building and zone, plan facility maintenance and legionella controls, manage complaints and their investigation, and keep the records required by regulations.

Limits and common mistakes

1. Reducing ventilation to save energy without guaranteeing minimum outdoor air flow rates.
2. Neglecting the maintenance of filters, ducts, trays and humidifiers, which become sources of biological contamination.
3. Attributing complaints to subjective factors without investigating or measuring them.
4. Introducing materials, furniture or cleaning products without considering their emissions or ventilating after construction work.
5. Forgetting about installations at risk of legionella or radon in high-risk areas.
6. Measuring a single parameter (carbon dioxide) and concluding that there is no problem without analyzing other sources.

The required environmental conditions are detailed in Royal Decree 486/1997, in the RITE and in the INSST technical guide on workplaces; this sheet is for informational purposes.

Regulatory and reference framework

• Royal Decree 486/1997, of April 14. Workplaces ; Annex III on environmental conditions, temperature, humidity and air renewal.
• Royal Decree 1027/2007, of July 20. Regulation of Thermal Installations in Buildings; indoor air quality, ventilation and maintenance of installations.
• Royal Decree 487/2022, of June 21. Health requirements for the prevention and control of legionellosis.
• NTP 243: Enclosed environments: air quality (INSST) . Parameters, pollutants and evaluation criteria.
• NTP 431: Characterization of air quality in indoor environments (INSST) . Research and measurement methodology.
• NTP 380: Sick building syndrome: simplified questionnaire (INSST) . Survey tool for occupants.

The INSST NTP 289 describes the risk factors of sick building syndrome, the UNE-EN 16798-1 standard the environmental design parameters and the UNE 171330 the inspection of indoor environmental quality; Royal Decree 1029/2022 regulates protection against radon in workplaces .