Isle of Wight Council bosses have overturned a vote by councillors - who had rejected the partnership to secure £900 million of funding.
Emergency Services' Hazardous Chemical Response Tested
Hampshire's police, fire and ambulance services will test how well they work together in situations involving hazardous chemicals.
Exercise Cameron will use HM Naval Base buildings in Portsmouth to test multi-agency emergency preparedness and response plans to a spontaneous hazardous material release. The exercise is being held within the naval base to enable emergency services to work together in an area that simulates an inner city urban environment including terraced housing in narrow roads.
Approximately 400 personnel and volunteers from response agencies including the emergency services, Portsmouth City Council and students from Portsmouth and South Downs College are taking part.
The exercise will test the interoperability of different agencies from across the region, plus the initial reconnaissance and mass decontamination facility.
The exercise lasts around seven hours, and will be assessed by the Hampshire and Isle of Wight Local Resilience Forum, which is chaired by Chief Constable Andy Marsh.
Chief Inspector Clive Marsh, who leads on Chemical Biological Radiological and Nuclear issues for the force and is a director of the exercise, said:
"We are gathering to put our officers and staff through their paces and ensure we are effectively prepared for any potential contingency. Our message to anyone who sees the vehicles and officers gathering is to not be alarmed - it is simply an exercise to make us better prepared for any eventuality.
"All agencies taking part on the day are committed to ensuring we can provide an excellent professional collaborative response to such risks and this exercise provides us with a rare opportunity for all involved to rehearse our response together."
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