In 2007 Airzone was called in to supervise and provide clearance sampling for a major mould remediation project in an apartment building in Toronto. Extensive mould growth was discovered in one unoccupied apartment caused by a hot water pipe leak. The particular challenge was to manage the remediation while minimizing disruption to other occupants of the building. Initial removal of damaged drywall led to the decision to completely gut the contaminated apartment and an adjacent (and similarly unoccupied) apartment. Post-remediation clearance samples did not show compliance immediately and the remediation contractor was called back to re-clean the gutted apartments. The repeat set of clearance samples confirmed that mould levels in the gutted apartments had returned to normal. Airzone used a unique technical approach in this case by using statistical sampling methods to show compliance.