About microbial fouling - legislation and scientific studies

Regardless of the construction phase in new production or in existing buildings, the law states through the Environmental Code and the Planning and Building Act that growth that can cause damage or inconvenience to human health must be removed. The legislation on chemicals emphasises that damage resulting in the need to use chemical products and pesticides should be avoided if knowledge and techniques for this are available. Once pesticides are used, only the intended use according to the instructions is authorised. Scientific studies and authorities advise against the use of chemical agents to clean up growth on wood. The reason is that they seem to have a limited effect and their use carries the risk of increasing the amount of pollutants in the indoor air. There is also a risk that the methods may only kill the microbial growth without removing it, and that even dead/inactive growth may pose health risks.

The research on moisture damage and negative impacts on human health is complicated to evaluate. It requires assessment by medically qualified people and demonstrating the links between moisture damage, growth and health parameters. The challenge is to define the boundary between harmful and non-harmful.

Decontamination of wood

Microbial growth on wood is remedied, using various decontamination measures to clean the wood material from the growth, unless the wood material is completely replaced. In the construction phase, if the building has been exposed to precipitation or if protection against moisture and water damage has been inadequate, there is a risk of damage. Moisture safety needs to be prioritised to a greater extent in many cases, and relevant strategies for managing moisture safety are already needed when planning the budget and design. The interviews with, among others, remediation companies in the project "Remediation of microbial damage to wood in buildings - a compilation of the current situation in the industry, laws, methods and areas of use" show that sanding of wood surfaces is the most commonly used remediation method, followed by ice blasting and the use of chemical agents to clean and bleach the wood surface.

Buildings that are exposed to free water or high moisture levels over a long period of time can suffer from rot and insect damage. Decay and insect damage is addressed by replacing damaged material and/or treating with authorised pesticides.

Moisture damage

Events where water to a greater or lesser extent causes damage to wood in buildings can occur. Prompt action and limitation of water exposure results in significant savings as the onset of typical moisture damage and the start of microbial growth can be prevented. During the construction phase, it is important that the organisation is prepared for incidents and can act quickly. In existing buildings, if and when preparedness is lacking, the time for detection of water exposure and before action is taken can be long and thus the risk of typical moisture damage occurring is high. Unlike water exposure to clean water, exposure to wastewater or other water containing microorganisms and contaminants always requires remediation.

Addressing moisture damage - industry practice and remediation

When moisture damage has occurred on wood in buildings, one typically thinks of visible mould growth and the smell of an earthy cellar. This is only partly correct because mould growth is not always visible to the naked eye. The limit of what is considered to be affected by mould growth in the wood structure and therefore damaged is not easy to define. Industry practice is used here, with sampling and analysis and assessment of growth with subsequent remediation and follow-up of the effect with new sampling.

Remediation of moisture damage

Remediation of moisture-damaged wood is mainly carried out by sanding the wood surfaces followed by blasting with carbon dioxide rice and, to a lesser extent, planing. The use of chemical products is also common, including cleaning agents, pesticides and/or general chemicals. The Environmental Code is the basis for the requirement that operators must have knowledge of the activities being carried out. There is also a requirement to avoid unnecessary use of chemical products.

Mechanical decontamination

Mechanical methods mean that the growth is physically removed with an object. Physical and mechanical removal methods are not regulated by pesticide laws. Methods include examples such as sanding, planing, blasting and scraping. The choice of mechanical method should be adapted to the substrate and the type of damage (see the section on standards above). The contractor should know how much of the surface layer of the infested timber needs to be removed in order to make the surface free of microbiological growth while avoiding unnecessary removal of material. It is also important to consider the working environment for those carrying out the decontamination and/or being in the vicinity of the decontamination area. There are level limit values for organic dust and wood dust (AFS 2018:1).

Chemical products - detergents

Detergents follow the legal requirements of the Regulation and EU level detergents. These products should have a good cleaning effect without being harmful to human health or the environment within the defined area of use. Pesticides are used in two categories which are surface disinfectants and wood preservatives. Disinfectants have a control effect that is temporary (< 3 months); as wood is a porous material, it is more difficult to disinfect and the effect is short-lived, only a few days. Wood preservatives with a longer-term effect used in existing buildings to protect or control organisms must be authorised for this purpose. The main requirements are that the product must have a proven benefit, be effective and not cause unacceptable damage to human health or the environment. Historically, there have been products that caused environmental and health problems and lacked efficacy for their intended use.

An agent that works against one type of organism does not always work against another type of organism. For authorised use, the right effect on the target organism with the right application method and dosage needs to be matched. Chemical products intended for the control of organisms can be effective when other methods of remediation are not available. A balance needs to be struck between the overall benefit and the risk of damage caused by chemicals. The benefit can be positive from a sustainability perspective, with savings for the environment and the economy. There are a few examples where chemical pesticides have a clear benefit. Infestations of dry rot and other mould fungi occur regularly in wooden buildings where water damage has occurred over a long period of time. Remediation requires the identification and removal of the cause of the water damage and the demolition of parts of the structure affected by the mould. As the fungal hyphae can travel 10s of metres from the water damage, the entire building would need to be demolished to ensure that the entire infestation is removed. To do this, chemical treatments are applied to the remaining timber so that any residual fungus cannot continue to grow in the event of further water damage. Similarly, timber foundations, with piles and rust beds, can be similarly saved in the event of a rot fungus infestation, avoiding the need for piling a new foundation structure and resulting in significant savings.

Chemical products - general chemicals

General chemicals, which are also pesticides, are sometimes incorrectly used to sanitise wood growth. Ethanol used for hand disinfection and for disinfecting non-porous surfaces in buildings has a proven effect over a number of hours. On wood, which is porous, this favourable effect is lacking as the ethanol is absorbed into the wood and the concentration decreases rapidly. In addition, there are organisms that can use ethanol as an energy source which can make the attack worse. Due to ignorance, ethanol is very commonly used as a sanitising agent against wood growth in buildings because ethanol-based products are readily available.

This is an article from our magazine Trävärden, view it here! (Link)

The Swedish Building Regulations (BBR 18 6:52) state that well-researched and documented critical moisture conditions should be used during the design and construction period. If this does not exist, 75% RH should be used as the critical moisture condition for mould growth. Moisture levels in building components vary in different parts of a building, as different activities and premises are more humid than others. Choosing a product that has a higher critical moisture condition than the expected moisture level in the building element reduces the risk of mould growth. 

Mould growth in a building is a consequence of moisture either as humidity or the introduction of free water through, for example, water damage or condensation. If the relative humidity RF in a building section exceeds 75% at room temperature, there is a risk of mould growth on the building materials. This level is a general minimum level but not all products will grow mould at this level. This is because the threshold for mould growth on a material varies between different products. Some products can be exposed to high moisture levels without mould growing on them, while others grow at lower levels. This property is described by the critical moisture state of the material with respect to mould growth. The difference between different products' critical moisture conditions for mould growth is that they contain different amounts of organic nutrients for the moulds to grow on.

There are no standardised values for the critical moisture condition for groups of building materials. The critical moisture condition can be affected by various factors, including any additives in the material and layers on the material surface. Research shows that different products within the same material group, such as plasterboard, wood fibre board or wood fibre insulation, can have significantly different properties and limit values for mould growth. Therefore, it is impossible to estimate or guess the critical moisture condition for a product group; it needs to be determined for each individual product within the group.

The critical moisture content of a material is determined by testing the product in the laboratory in a standardised way. According to the test method, the products are tested at four different moisture levels at +22°C The critical moisture state is affected by temperature and if it is colder, more moisture is needed for mould to grow. The method includes an equation to calculate the critical moisture condition at temperatures other than the constant temperature of +22 °C used in the test. It is important to point out that the critical moisture condition of a product is not a measure of how good or bad it is. Instead, it is an aid to making informed decisions on the choice of materials for building elements where the moisture level is known. To reduce the risk of mould-related damage in buildings, more actors in the industry would need to recognise the importance of using critical moisture conditions in the design of buildings. To facilitate this work, more material manufacturers need to choose to test and report the critical moisture condition on their products.

This is an article from our magazine Trävärden, view it here! (Link)

An aerosol is a mixture of small particles or liquid droplets suspended in a gas, such as air. They affect our health and can be linked to allergies, respiratory diseases, cardiovascular diseases, and cancer. Aerosol particles occur naturally, such as pollen or droplets formed when we sneeze, but are also a result of emissions, wear and tear on roads or tires, combustion, and industrial processes.

“Certain metals have been specifically linked to negative health effects. There are methods to measure the concentration of aerosol particles in the air, and the metal content in them, but to better understand the actual causes of the negative health effects, or determine where the particles come from, we need to continue to develop measurement methods”, says Jenny Rissler, senior researcher in aerosol physics and expert in X-ray spectroscopy methods.

Calibrated Measuring Instruments Require References

For reliable measurements, calibrated measuring instruments are needed, and to calibrate measuring instruments, something to compare with, a reference, is needed. By developing better references, in this case for aerosols with very well-known properties, one can evaluate and develop measuring instruments and methods. This is, among other things, what the European research project AEROMETII has worked on.

“At RISE, for example, we evaluated how different low-cost instruments for aerosol measurements perform in different environments, at different places, in different temperatures, and so on. Advanced instruments are often more precise, but it's also important with cheaper instruments since this enables more measurements and in more places. At the same time, these instruments are often limited in their performance, and it's important to have knowledge about what the limitations are and when they work as well as the advanced instruments. In another work package, we looked at what chemical form metals in aerosol particles from different European cities have”, says Jenny Rissler.
 

Chemical Form Affects Health Effects

The chemical form of a substance, i.e., what chemical compound the atoms form, can vary depending on how and where the particles were formed.

“For example, zinc in particles generated from tires probably forms other chemical compounds than zinc in particles from brakes, and lead from a battery factory forms different compounds than those from traffic related emissions. With better knowledge, we could trace the origin of different particles based on their chemical form and use this information to improve air quality.”

For some elements, it has been seen that the chemical form also affects health effects. Through developed methods to characterize chemical form, we can contribute to continued research on these health effects.

The Beamline Balder

In the AEROMETII project, Jenny Rissler and her colleagues used advanced spectroscopy techniques at the beamline Balder at the synchrotron laboratory MAX IV in Lund.

“We used x-ray absorption spectroscopy to compare samples from different parts of Europe, and could see that the chemical form of, for example, zinc actually differed depending on where the sample came from. But more research is needed, this was one of the first European studies. Most previous studies have been conducted in China.”

Pollen Measurement with AI

In the coming years, the plan is for aerosol research to continue along with European colleagues.

“Emissions from traffic and roads would be interesting to investigate. If we assume that exhaust gases decrease because of electric car development, aerosols still remain as an effect of wear and tear on roads and vehicles, for example, from brakes or tires.”

This summer, the project BIOAIRMET, which deals with measuring and quantifying pollen, will also start.

“When measuring pollen today a lot is done manually, but in this project, we want to develop new AI methods. To do this, reference pollen, i.e., pollen with very well-known properties, is needed, which we can use to teach the AI system to measure correctly. These references will be developed in Switzerland, and then we at RISE will characterize them so that we know what chemical and physical properties they have”, says Jenny Rissler.