Feature article: Air humidification protects health in the workplace

Over the past 20 years, the high demand for energy-efficient buildings has led to an increasingly dry indoor climate. Airtight buildings, large glass façades and the absence of ventilation systems now result in excellent energy efficiency in building technology. Unfortunately for those affected, poor planning can lead to indoor air that is far too warm and dry: Dry mucous membranes, burning eyes, tight skin, a hoarse voice – these are the symptoms of ‘Dry Building Syndrome’, which is making people ill in an increasing number of buildings.

The air we breathe surrounds us constantly and is our most essential resource: every day, up to 13,000 litres of air flow through our nose, mouth and lungs. We spend up to 90% of our time indoors. The quality of indoor air and its ability to protect us from pollutants and pathogens are crucial to maintaining our health. Recent studies have once again confirmed that relative humidity is of immense importance for the functionality and immune defences of the mucous membranes.

The indoor climate has many dimensions: how we assess the quality of the indoor climate is essentially determined by air temperature, humidity, air velocity and air quality. Each of these factors influences indoor climate quality in its own way. These climate factors interact with one another.

Temperature and thermal radiation

Air temperature is the key factor among the climate factors in the workplace. However, it is not the sole determinant of perceived temperature: “Physiological studies,” says ergonomics expert Etienne Grandjean, “on the interaction between air temperatures and the temperatures of surrounding surfaces have shown that a person’s perceived temperature corresponds to the average value between these temperatures.” Walls, windows, ceilings and floors are the surrounding surfaces in a room. As heat emitters, they have a noticeable influence on the temperature in the room. Several factors contribute to excessively high temperatures at the desk, particularly in summer: large window fronts, a lack of sun protection, and heat emitted by computers, photocopiers, printers and the lighting system.

If the air in the building remains dry, it is advisable to consult the building services team first. Poorly adjusted air-conditioning systems set to excessively high temperatures are often the cause. Overheated rooms cause the humidity to drop automatically. If the relative humidity remains below 40% for an extended period, additional mechanical humidification may be advisable.

Technical options for air humidification include central ventilation systems that can regulate humidity as well as temperature and fresh air supply. Humidity is delivered indirectly into the rooms via the ventilation ducts. This solution is frequently used in new buildings. In older buildings, retrofitting is often not possible, or only with considerable effort. One option particularly suitable for retrofitting is the direct room humidification. Unlike humidification within an air conditioning system, small nozzle humidifiers are installed directly in the room.

The direct room humidifiers are mounted almost invisibly on the wall or ceiling, where they spray a microfine ‘mist’ of hygienically treated water as required. The additional moisture is immediately absorbed by the air in the room and distributed evenly throughout the office. The rapid evaporation also creates a revitalising, refreshing effect in the room air. The humidifiers are controlled by digital control units that only activate humidification when the humidity falls below the desired optimum level. With direct room air humidification, it is not necessary to equip an entire building. Individual floors or office areas (e.g. call centres) can also be humidified individually and cost-effectively. Any air humidification system is only as good as the maintenance and cleaning concept behind it. Even if the water used appears clear and clean, the substances it contains can pose risks to health and operational safety. Hygiene standards and systems with automated maintenance intervals reliably eliminate all risks.

Respiratory illnesses are among the most common causes of incapacity for work. In winter in particular, there is an increase in flu outbreaks and respiratory infections. Studies show that the immune system’s defences and the survival time of viruses depend directly on humidity. In addition, the voice, skin and eyes suffer. Medical professionals summarise the symptoms as ‘dry building syndrome’. Humans are not defenceless against attacks by viruses and bacteria: in the respiratory tract, the mucous membranes protect us from infections through their self-cleaning function. The mucous membranes in the nose and lower respiratory tract have fine cilia on their surface, which move freely in a thin secretion (sol layer). Overlying this is a sticky gel-like mucus layer to which viruses and bacteria can adhere. Through the rhythmic movements of the cilia in the thin sol layer, the mucus is continuously transported towards the larynx, where it can be swallowed or coughed up along with the pathogens. This self-cleaning mechanism keeps us healthy.

Aerosols carrying viruses and bacteria can remain suspended in the air for hours, depending on their size and weight, and are distributed throughout the building via the ventilation system. The risk of infection increases the longer they remain in the air. The intensity of turbulence and the forces of attraction on surfaces depend directly on the humidity in the room. Infectious aerosols from the respiratory tract remain water-laden up to an ambient humidity of 45% relative humidity, making them heavier and ‘sticky’. Their time spent in the air before settling on the floor or on surfaces is therefore much shorter. Furthermore, the forces of attraction between the water content and the surfaces cause the ‘moist’ aerosols to adhere more strongly and make them difficult to resuspend.

The risk of inhaling infectious aerosols is therefore significantly lower when the air humidity is sufficiently high, particularly with additional humidification. If the humidity in the workplace is below 40%, ‘dry’ aerosols containing crystallised salts are formed, which are smaller and lighter than ‘moist’ aerosols. As a result, they remain suspended in the air for longer, are less sticky and adhere less to one another. Ventilation systems and the activities of office users quickly stir up dry aerosols from surfaces (e.g. desks, cupboards) and spread them further. This significantly increases the risk of becoming infected by viruses that remain infectious for longer in the first place when humidity is low.

Dry air is particularly unpleasant and dangerous for professions involving extensive speaking and screen work. All too often, the direct link to the indoor climate goes unrecognised. A dry throat and larynx, throat-clearing and the urge to cough are always the first warning signs. By the time the voice sounds hoarse or is completely lost, work performance is already impaired. To maintain good vocal function and prevent vocal disorders, adequate moisturisation of the mucous membranes is essential: when speaking, air is forced from the lungs through the larynx. The vocal folds vibrate and, like the strings of a guitar, produce sound. If the air humidity is too low, the mucous membranes of the vocal folds lose their optimal moisture and, consequently, their elasticity. After inhalation, the glottis can no longer be completely closed by the vocal folds. Air leaks into the vocal tract, leading to irritation, inflammation and, in the worst case, loss of voice.

High temperatures in production areas and offices place an additional strain on staff. However, cooling workspaces requires high cooling capacity and results in high energy costs. Additional air humidification can offer a twofold benefit: on the one hand, the costs of using air conditioning units can be significantly reduced, and on the other hand, employee comfort and health can be improved.

Air conditioning in production halls requires high cooling capacity and results in high energy costs. The use of additional air humidification, with the appropriate technology and design, can reduce the costs of an air-conditioning system or lower the room temperature independently of an existing air-conditioning system. The reason for this is the adiabatic cooling effect that occurs when cold water is sprayed into the room air without forming droplets: the complete absorption of the micro-fine water droplets in the air ensures that heat is extracted from the room. The principle of adiabatic evaporative cooling results in an exceptionally economical reduction in room temperature: 100 litres of water from a high-pressure nozzle humidifier absorb around 70 kW of heat whilst consuming only 0.6 kW of energy. This enables an average reduction in room temperature of between 2°C and 5°C.