The site comprised an existing city centre building, which was undergoing significant refurbishment to accommodate a new private school. During preliminary works, intrusive investigation was undertaken within the basement to investigate the foundation construction and inform design.

When the concrete floor slab was breached, an audible hissing noise and an unexpected release of gas was identified. This unexpected release of gas was recognised as presenting a potential hazard to the drilling operatives, the building and other occupants, or visitors. As such, the pilot hole was temporarily plugged, and intrusive works were suspended until further investigation was completed and a safe system of work was in place.

GGS supported the implementation of a safe system of work by:

• Developing a system of control measures for a range of potential gases of concern, inclusive of RAG ratings and action levels.
• Provision of site-specific Risk Assessments and Method Statements (RAMS).
• Undertaking a high-resolution gas sweep survey of the basement area prior to works commencing to provide an indication of baseline conditions and ensure safe conditions prior to works commencing.
• Provision of a briefing to operatives regarding the control measures and action levels.
• A watching brief during intrusive works, with ground gas measurements recorded at parts per million by volume level to provide an early indication of the potential release of ground gas.
• A high-resolution gas sweep survey of the basement area once the intrusive works were complete to confirm that no adverse changes in ground gases had occurred following the works.

Outcome

GGS presence on site ensured that a safe system of work was in place to enable the intrusive works to continue and for the refurbishment to remain on schedule. A factual letter report was provided to The Client on completion of the works to remain on file and provide evidence that a safe system of work was implemented.