Perry residents who live near the Grafham Water Treatment Works were advised to move inside and close all windows and doors after a chlorine alarm sounded at 8am.Workers managed to contain the leak within the building at the Anglian Water plant by dousing the gas with water.At least 25 firefighters from Huntingdon, Sawtry, St Neots and Yaxley then worked with water company staff to ventilate the building. The leak also led to police closing the B661 from the Grafham junction and reiterating the warning that people should stay indoors. Chief inspector Mike Hills said that the precautionary measures have now been lifted and people are free to go about their usual business. He said: We put out the advice as a precaution following the leak of a very small amount of gas. The leak was contained to the building but it was necessary for us to release it into the atmosphere in a controlled process. The risk to the public was minimal throughout that process, however we felt it necessary to take the maximum precautions to ensure the public were protected. We would like to thank residents and visitors to the area for their cooperation and apologise for any inconvenience caused.