SPRINGFIELD, Mass. (AP) - The president of the gas company behind an explosion in Springfield, Massachusetts that injured 21 people says the employee blamed for piercing a gas line followed proper procedure and protocol.

The blast Friday that leveled an adult entertainment club and damaged 42 buildings was blamed on "human error." Investigators say the employee was following incorrect markings on a sidewalk that indicated the location of the gas line.

Columbia Gas of Massachusetts President Steven Bryant says the unnamed employee was following standard company procedure when he responded to the smell of gas.

Bryant said the employee had the presence of mind to order an "appropriate" evacuation of the building.

Columbia plans to open a claims center at City Hall on Monday for residents and businesses affected by the explosion.

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