Federal safety regulars are investigating how a Yale forklift broke through a Springfield concrete sidewalk, plunged backward into an open space and came to rest with its tynes, tilted at about 45 degrees toward the sky.

Region 1 of the US Occupational Safety and Health Administration has launched the investigation.

An unidentified operator using the MassMutual Centre-owned propane-powered forklift was moving large planter boxes as a favour for the Springfield Business Improvement District. Apparently, he was unaware the heavy equipment should not have been used on a city sidewalk.

He was treated for minor injuries at the Baystate Health System's medical centre in the city.

The 2 July incident caught the attention of motorists and pedestrians and slowed traffic. A crane was summoned to remove the forklift.

Speculation focuses on the possibility of the underground area formerly being used as a coal chute, a delivery opening or perhaps a cellar.

The Massachusetts Convention Center Authority owns the MassMutual Centre for which the Massachusetts Mutual Life Insurance Co has naming rights.