Perry residents who live near the Anglian Water plant have been advised to close all windows and doors after a chlorine alarm sounded at 8am. Anglian Waters head of communications, Ciaran Nelson, said the leak had been contained to a storage building but the gas needed to be dispersed. He added: In order for us to get in and repair where the leak is we need to do a controlled vent of that building. When we do that its a standard matter of process that chlorine alarms go off, so in the village of Perry, the alarms will have gone off. The best advice is to get indoors and shut doors and windows. Then theres an all-clear alarm which will be a couple of hours after the first alarm goes off. Theres not very much for people to worry about - theres no risk to public health at all. At least 25 firefighters from Huntingdon, Sawtry, St Neots and Yaxley are working with water company staff to ventilate the building. Mr Nelson said that the gas would be doused with water as it was dispersed which meant it would not leave the site. Police shut the B661 from the Grafham junction and reiterated the warning that people should stay indoors. Inspector Mark Greenhalgh said: As a precautionary measure we are advising the public who are within 1,300 metres of the site to go immediately into a house or building, close all doors and windows, turn off all ventilation and central heating systems. We have experts at the scene assessing the situation and would urge people not to panic. We will put updates out on our website and via the media as and when we have them.Keith Morton, landlord of the Wheatsheaf pub, which was within the cordoned off area, said he hoped the emergency would not affect trade. Its a Friday, the suns out so I thought we were going to be rammed, so we could do without this to be honest. Perry residents were familiar with the alarm, he said, as it was tested every Wednesday. No one is panicking, he added. Weve still got cyclists turning up.