The details of our work at the direction of the customer included contact HEPA (high efficiency particulate air) vacuuming 17 return air risers serving the second level of the podium section of the casino. HEPA vacuums and filters can trap 99.97% of particles 0.3 microns or greater. Risers were cleaned 20 feet upwards or to a turn. Fire dampers in all 17 risers were contact HEPA vacuumed and hand wiped. In addition, return ductwork for AHUs 6 and 10, where reachable and accessible, were contact HEPA vacuumed inwards of 20 feet or to a turn.