New Delhi, Oct 23: The fire that started at the sprawling Bhalaswa landfill site here on Sunday is continuing for the third day on Tuesday, while a very poor quality air is choking Delhi.The fire-services said that while four tenders are already trying to douse the fire, two more have been sent to the site. Municipal engineers said they have procured more debris to cover the exposed area to extinguish the fire.The inferno on Delhi's second largest un-engineered mountain of garbage started due to gaseous fumes. The 40 m tall oversaturated landfill that spreads over 50 acres is located amid one of the most populated regions of Delhi. "The fire usually starts due to formation of methane gas within the layers of garbage," Sanjay Jain, Engineer, Department of Environment Maintenance Services (DEMS) at North Delhi Municipal Corporation (NDMC), told IANS.Meanwhile, harmful chemical vapours and gases from the landfill site started showing its effect as the nearest air monitoring station to the Burari Crossing area showed "severe-plus or emergency" air-quality. The major pollutant PM2.5 or particle with diameter less than 2.5 mm in Burari Crossing was 333 units at 3 p.m. on Tuesday, while the national standard is 60 units and international standard is 25 units.About 2,000 tonnes of mixed garbage is dumped at Bhalaswa everyday. According to the 2016 solid-waste management rules, a landfill site must not exceed 20 m in height, must not be older than 22-25 years and must have a clay-lining at the bottom to save the land and ground water.