We've got him! The first of no-doubt many official reports on the 2012 Big Utrecht Asbestos Scare (BUAS) (pdf). See the earlier blog report here. The first surprise is no surprise at all: the asbestos levels in the affected apartments were insignificant. The asbestos varieties that have been found are amosite and chrysotile, An earlier report report mentions X-ray microanalysis and SEM as analytic tools (measurements in fibers per square meter). The Dutch norm is NEN 2991 but for some reason it costs 30 euro's to read it. Sorry! The international norm is ISO 14966 and also costs money. The closest public source if you are interested can be found here.
The presence of asbestos variety amosite did come as a surprise because according to the report it is never used in building homes. It was used in a type of sealant for a part of the roof. The report does not have anything to offer in terms of an explanation but in a radio interview one of the authors speculated that at one point during construction of the building (1960) a worker was looking for sealant and stumbled upon this particular amosite containing batch. Thanks a lot, worker! 52 years down the road you caused a mass-panic! Well, it goes to prove that accidents more often than not are freak accidents.