Investigation of ill health in an office located below ground

The project

Complaints of poor indoor air quality led to an assessment of a 2 storey concrete office building with one storey underground. A detailed screening assessment identified excess volatile organic chemicals (VOCs) with highest levels in the underground floor, particularly at the base of the walls.

Further investigation indicated that the building had been designed with a crushed stone drain surrounding its perimeter, a sound engineering practice to prevent water intrusion and hydraulic pressure on the concrete walls of the below-ground level floor. However, leakage from an underground storage tank containing petroleum products on an adjacent property had caused contaminant flow into the drainage conduit. Once there, with little resistance to flow, it rapidly moved as both a liquid and a vapour, completely around the building.

Unfortunately, negative pressurisation from the building’s HVAC system due to poor operational characteristics then sucked these vapours through the concrete below-ground foundation walls, into the occupied space, creating the observed contamination and health symptoms.

The outcome

The building owner was able to take immediate steps to modify the HVAC system to ameliorate the issue, minimize risk to workers and other occupants of the office space, and notify the adjacent property owner to rectify the source.