Medics, the military and the emergency services are taking part in a major exercise to see how they would cope in the evacuation of a hospital.
Around 140 people are involved in the operation at the Friarage Hospital in Northallerton, where a disused ward has been filled with smoke to simulate a fire.
Doctors, nurses, the Fire Service and Ambulance Service are working to evacuate the ward, which has been filled with hospital staff playing the roles of patients.
The exercise director says they are aiming to create as real a scenario as possible so the teams are equipped to deal with an actual emergency.
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Dry, warm and sunny with sea breezes. Isolated heavy showers by evening and overnight