Methane gas at levels that could explode has been detected at the 2025 World Exposition site in Osaka City, western Japan.



The Japan Association for the 2025 World Expo has pledged to tighten measures, as a methane explosion occurred at the same area last year.



The association says methane gas with a concentration level that could explode if ignited was detected at the basement in the Green World area on the northwest side of the expo site on Sunday.



A visitor with a detector who was attending a test run of the Expo reported the finding to firefighters. The area was ventilated for about half an hour and the gas was no longer detected.



In the same area in March last year, there was an explosion of methane gas triggered by a spark from construction work. The association then set up fans in the building's basement to ventilate the area to remove the gas.



Workers also periodically check levels of the gas in underground spaces and ventilate the gas.



As the gas was detected in an area subject to these preventive measures, the association says it will carry out checks three times a day instead of once a day, and increase observation points from two to seven locations.



Deputy Secretary General of the association, Takashina Jun, explained that when methane gas is detected underground, it does not pose immediate danger because it disperses when it reaches above ground.



He added the association will take all-out steps to confirm the safety of visitors.