A portion of the Giaspura locality in Punjab's Ludhiana where 11 people died allegedly after inhaling toxic gas remained cordoned off on Monday while the district authorities said the affected area underwent a night-long decontamination process. Teams of the Punjab Pollution Control Board checked what led to the buildup of Hydrogen sulphide in the sewer that might have led to the tragedy, the officials said, adding that the poisonous gas is no longer being detected in the air. Eleven people, including three children, died after allegedly inhaling toxic gas in the city's thickly populated Giaspura locality on Sunday, with high levels of Hydrogen sulphide detected in the air and authorities suspecting that it emanated from a sewer.