In the United States, two companies which process perlite were visited and interviews taken; there was also a meeting with the representative of the perlite association, with whom an interview was also taken.
Í Bandaríkjunum voru heimsóttar tvær verksmiðjur sem eru að þenja perlustein og tekin þar viðtöl og síðan hitti rannsakandi einnig forsvarsmann perlusteinssamtakanna og tók við hann viðtal.