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 environments that are not hot or polluted by tobacco smoke, 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 flow rates and filtration and maintenance requirements.

Parameters, evaluation and measures

• Carbon dioxide. An indicator of air renewal under certain occupancy conditions; the reference of 1,000 parts per million can flag inadequate ventilation, but is not a universal safety limit and does not rule out other pollutants.
• 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 under the applicable RITE program, including required duct and environmental quality reviews and their UNE references, 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 .

Sustainable materials: check emissions as well as their origin

A refurbishment may reduce energy use or incorporate renewable raw materials while introducing substances that worsen indoor air. Paints, adhesives, sealants, finishes and furniture should be assessed according to their composition, use and foreseeable emissions. Sustainable describes several different environmental objectives; the word alone does not establish the absence of formaldehyde, volatile organic compounds or particles. Preventive selection requires product information and assessment of the complete construction solution, including auxiliary materials introduced during installation that may not appear in the main product description or headline environmental claim.

The EPA distinguishes volatile organic compound content from emissions into indoor air. Some declarations concern rules addressing outdoor photochemical pollution; others are based on emission testing. It is therefore useful to check what each label certifies, which substances it measures, under what conditions and for which use. An aggregate volatile organic compound result does not necessarily identify the substance responsible for discomfort. This technical distinction helps obtain relevant information from suppliers without treating a foreign certification as a Spanish legal requirement or dismissing every environmental label as meaningless.

The construction plan should address segregation, storage, application, drying and ventilation before reoccupation. No single number of hours guarantees safety after every refurbishment. Relevant factors include quantity applied, curing conditions, room volume, air renewal and the presence of sensitive people. The Spanish Ministry of Health’s 2026 guide includes materials, refurbishment and maintenance products in hazard identification. Before reopening an area, implementation of the planned measures is verified and specific contaminants are checked with appropriate methods where the assessment requires this. Reoccupation should follow the actual conditions rather than a generic countdown.

Sick building syndrome: investigate patterns without automatically assigning causes

Discomfort that begins or worsens during time spent in a building and improves after leaving can guide an environmental investigation. This timing alone does not identify an agent or establish an individual diagnosis. Sick building syndrome describes a pattern of nonspecific symptoms; it should be distinguished from diseases with an investigable cause, such as carbon monoxide poisoning or legionellosis. The description also does not establish that everyone working in the building is ill or that every complaint has the same origin. Environmental evidence and clinical findings need appropriate interpretation.

Investigation starts by listening to occupants and identifying when, where and during which activities discomfort occurs. Changes in layout, occupancy, cleaning, construction, dampness and system operation are compared. Different shifts, cleaning personnel and contractors should be included because their exposures may differ from those of office staff. A questionnaire organizes information, but requires adequate participation and cautious interpretation: no response does not mean no problem, and an association with one area does not prove causation without examining other possible explanations and how information was collected.

Technical assessment and healthcare should be coordinated while maintaining clinical confidentiality. The employer needs preventive measures and conclusions rather than individual diagnoses disclosed in a maintenance report. Complaints should not be dismissed because an initial visit finds no anomaly or automatically attributed to psychological factors. Where an immediate danger is suspected, protective action should not wait for a survey to be completed. For persistent problems, hypotheses, checks and measures are documented so repeated measurements answer an actual investigative question. Workers should know how concerns are being assessed and followed up.

Ventilation and CO₂: interpret context and distinguish filtration

Carbon dioxide can help assess air renewal when occupants’ breathing is its main source. Interpretation requires knowledge of occupancy, activity, outdoor concentration, measurement duration and sensor position. A reading beside a person, window or supply outlet may poorly represent the room overall. Combustion or other processes can also invalidate an interpretation based only on people. Records should distinguish a brief peak from a recurring trend during normal operation and identify relevant changes in room use. The instrument’s capabilities and location must be suitable for the question being investigated.

RITE criteria depend on the category and calculation method selected; some CO₂ values express differences from outdoor concentrations. They should not be compared directly with absolute concentrations without identifying the criterion. The commonly used reference of 1,000 parts per million can flag inadequate ventilation in certain occupied spaces, but is neither a certificate of safe air nor a universal infection threshold. A low result does not rule out formaldehyde, radon, carbon monoxide or task emissions. Each problem needs indicators capable of detecting it rather than a single reassuring number.

Experience during the pandemic reinforced the importance of air renewal and distribution. Recirculating or cooling air does not necessarily provide outdoor air. Filtration may reduce particles depending on the filter, airflow and equipment, but does not automatically remove gases or replace every ventilation requirement. Compatibility, capacity, noise and maintenance are checked before filters are changed or equipment added. Ventilation belongs within a combination of measures against respiratory infections; alone it does not guarantee absence of transmission or justify overlooking other applicable precautions. Technical changes should be evaluated in the actual occupied space.

Central air conditioning: protect occupants and maintenance personnel

The maintenance program should correspond to the installed system and its manual, considering the operations and frequencies required by Spain’s RITE. Outdoor intakes, airflow routes, filters, heat exchangers, drainage, condensate trays and humidification components are examined where present. Replacing a filter is insufficient if water ingress continues or an intake remains beside a pollution source. Refurbishment, closures and changes of use should also be checked for altered airflow distribution, which can leave areas insufficiently ventilated even when the main equipment operates. System operation and actual room conditions must be considered together.

Maintenance may expose personnel to moving parts, electricity, cleaning chemicals, accumulated dust, biological agents and difficult access. Energy isolation, safe access, cleaning methods and waste handling should be planned. Annex II of Royal Decree 1215/1997 requires specific conditions for hazardous maintenance operations, including preventing accidental restart. Spraying disinfectant without an assessment or procedure does not establish effective cleaning and may add chemical exposure. The intervention area is protected to prevent dirt spreading into occupied spaces. Protection of building occupants cannot be separated from the safety of those maintaining its systems.

Legionella prevention is assessed according to installation type and the potential for growth and dispersal through water aerosols. Equipment that only moves or cools air should not automatically be equated with a cooling tower. Installations covered by Royal Decree 487/2022, updated in 2024, must meet the relevant plans and controls. Article 9 addresses the Legionella Health Plan and requires retaining the PPCL until that alternative is adequately designed, planned and validated through data or results demonstrating effectiveness. Choosing a different plan name does not remove the need to control the installation.

Improvement planning: measure what matters and verify the result

A useful plan identifies those responsible for the building, maintenance, prevention and concurrent contractors. It brings together drawings, installation inventories, recent changes, operating records and incidents. The 2026 Spanish technical and health guide proposes assessment combining visual examination, documentation and justified testing. Not all its technical references are legal limits applicable to every building. The applicable legal requirements, technical method and intended objective should be identified separately. This prevents a voluntary certification from being presented as complete compliance with every occupational safety and health obligation relevant to the premises. The 2026 health guide distinguishes UNE 171330:2024, which it uses as a technical reference, from UNE 171330-2:2014 referenced by RITE. A new technical edition does not by itself replace the regulatory reference.

Measurements should represent relevant areas, times and operating conditions. Instruments, methods, checks, locations and limitations are recorded, including the influence of outdoor air. An inexpensive volatile organic compound sensor may help observe trends within its capabilities, but does not identify every substance or replace a specific analysis when required. Results are interpreted alongside sources and activities. Energy efficiency should improve while adequate air renewal is maintained; closing outdoor air supplies to reduce a bill should not shift costs to health or comfort. Follow-up must reflect ordinary occupancy rather than unusually favorable test conditions.

In a hypothetical example, a refurbished office develops complaints after new furniture and increased occupancy. Installed products, airflow distribution, operating hours and possible dampness are reviewed instead of attributing everything to one CO₂ reading. Actions may combine source control and ventilation adjustments, followed by checks under comparable conditions. Closure requires confirmation that measures were implemented and the problem decreased without creating another. Occupants are informed about results and unresolved issues through an accessible follow-up channel. This gives the investigation a practical endpoint while allowing it to reopen when conditions change.