Update at 4:48 p.m.: One man was killed, one critically injured and four others transported by ambulance to Brooke Army Medical Center, said Robert Hogan, fire chief of Bexar County Emergency District No. 10. Hogan said the deceased victim was discovered inside the oil tanker. One victim was found on top of the tanker and was airlifted to BAMC. The other victims were taken by ground ambulance. The victims were cleaning residue in the tanker when the explosion occurred, Hogan said. Original story: A rail tanker explosion resulted in at least three injuries Friday afternoon in south Bexar County, said Eric Maldonado, Bexar County Precinct 4 spokesman. Maldonado said four people were working inside a tanker at the Alamo Junction Rail Park, in the 12500 block of Old Corpus Christi Road, which is near Braunig Lake and Interstate 37, when the explosion occurred. Three victims suffered thermal injuries. It's unknown if the fourth worker was hurt, Maldonado said. A woman told KSAT's Garret Brnger that police notified her that her 23-year-old son is trapped. She could not go into further detail. VIDEO: Officials hold news conference on tanker explosion Two Airlife helicopters are at the scene, as well as the San Antonio Fire Department Hazmat unit. Officer Glenn Harlow, with the Elmendorf Police Department, said there is no longer an immediate danger and the fire is contained. While there are multiples companies at the Alamo Junction Rail Park, Harlow confirmed with KSAT.com that the explosion happened at the station of CRU Railcar Services. Crews with SAFD, Bexar County Fire Marshal, China Grove Fire Department and Wilson County Fire Department are at the scene trying to determine what led up to the explosion, Harlow said.