Following the accident at Pachiayappa’s College Metro station, security has been stepped up at the Nehru Park Metro station, sources said. An external agency will check the equipment once in six months. Officials at the site have begun to undertake a safety audit every week.

“We will test the condition of the rope, boom and automated safe load indicator of the crane. The safe load indicator shows the safe working load for every crane. So, the operator is guided to choose the type of load by using the safe load chart. The safety and maintenance department inspects this and give a green card which indicates the crane is fit,” a source said.

Also, proximity sensors have been placed at the site, he said. For instance, if a worker accidentally walks close to the crane, the sensor detects it and the crane automatically stops; this is present only at this site.

The concrete structures used by the Tunnel Boring Machines (TBMs) to connect underground stations are also under no risk as they are pre-cast structures manufactured at a factory in Vayalanallur in the outskirts of the city, a source said. “During the excavation, the cutter may hit a manhole filled with toxic gases and release them. The workers are provided with portable and standalone gas analysers which instantly detect the discharge of such gases and the workers can use oxygen masks provided to them and leave the tunnel at once. Fire extinguishers are placed at every 50 metres inside the tunnel. The workers are also educated and trained to handle the equipments,” he said.

A construction expert said that a pre-cast structure will never fall because the concrete is allowed to set in the factory. The precast concrete ring structures are tested by IIT labs.

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