Mr Hardwick also said that, if there were to be an emergency, "the dysfunctional cell call bell system gave us no confidence that officers would promptly attend".

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Dr. Mark Bell, principal of Emergent Medical Associates, which operates 18 emergency departments in Southern California, said the level of fear is unprecedented.

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"We have had a lot of nervous patients with minimal respiratory tract symptoms, " said Dr. Mark Bell, principal of Emergent Medical Associates, which operates 18 emergency departments in Southern California.

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It used to be that if a town wanted to communicate to its residents that there was an emergency, there was one tried-and-true method: ring a giant bell.

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And in Santiago, Chile, short-term emergency action was taken in the 90s when there were extraordinary bursts of smog, says Nigel Bell, professor of environmental pollution at Imperial College London.

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