Flanders is hoping to put an end to the historical asbestos pollution in its building heritage and is therefore calling on remote sensing expertise of VITO and the Flanders Information Agency (AIV) for the inventarisation process.

Belgium was once a country that was highly contaminated by asbestos, and we still carry this historical legacy with us in our building heritage. According to estimates by the Public Waste Agency of Flanders (OVAM), there are still about 2.3 million tonnes of asbestos in homes, schools, businesses and other buildings today. A large part of that asbestos can be found in corrugated roofs and slates. This not only poses a risk during demolition work, but there is also a threat to the local environment (as well as health) as a result of weathering of the roofing due to exposure to natural elements and the ability of the released asbestos fibres to spread easily.

Asbestos plan

The Flemish government has asked OVAM to devise an ambitious 'asbestos plan', with the aim of making our region asbestos-safe in the long term – which means that during normal use of a building there should be no more risks from the present asbestos materials.

One of the key actions of the plan is the gradual removal of asbestos cement roofs, facades and cable insulation by 2034. By 2040 all other hazardous asbestos materials should be removed.

Unfortunately, there is hardly any geographic information available on the spread of asbestos in the construction industry in recent decades. That is why OVAM has called upon VITO and the Information Agency to use its remote sensing techniques to support the asbestos inventory for Flanders.

Archive images

"We began by looking at which data is available and to what extent we can use this data to identify asbestos roofs from the air", explains Jan Biesemans of VITO. "During that exercise, we learned that multispectral aerial images (RGB) with a resolution of ten centimetres or more are sufficient for recognising corrugated sheets and slates to an acceptable level of accuracy. The major benefit here is that, thanks to the Information Agency we already have these images for the whole of Flanders, the result of an intensive measurement campaign that ran from 2013 to 2015 within the framework of the Flanders II Digital Altitude Model."

VITO and the Information Agency are now compiling the first aerial map based on these images. Biesemans explains: "Just to be clear, this is a map of potential occurrence. It therefore indicates where asbestos roofs could be located." VITO researchers, together with AIV and Passwerk are also responsible for processing the images and thus detecting roofing containing asbestos. They are using new technology from the field of artificial intelligence in order to achieve this. Together with the AIV, VITO developed a number of deep learning models that were then specifically trained for this task.

How can the researchers use their images to establish when a building was erected or a roof was laid or renewed? "The year of construction cannot be deduced form an image, but in a later phase, combined with historical photographs, the year of construction can be determined more accurately and by doing so, we can better assess whether the roofing contains asbestos or not. If there is still any doubt in a specific case, an expert will need to visit the site", explains Biesemans.

According to Astrid Verheyen of the OVAM asbestos phase out team, the remote sensing approach also provides a useful tool for raising citizens' awareness and informing them about actions that support asbestos removal. “With a possible combination of the solar map and the information on asbestos removal we could give more targeted advice about the locations where asbestos removal followed by the installation of solar panels is profitable and for which locations the (target) milestone of 2034 is applicable.”"