Cheyenne, WY – Loud explosions were heard and massive flames were seen Monday afternoon at the Frontier Refinery in Cheyenne. Frontier Community Relations Manager Selina Hoflund says there were no injuries due to the incident. She says the fire started in the Coker Unit, where asphalt is made into coke used when refining oil. Holfund was at the refinery when the explosions occurred and says it sounded like a sonic boom or a sound that trains often make near the refinery. According to Hoflund, there are between five and ten people working in that area at any given time. But fortunately she says everyone was on break when the explosions happened. Hoflund says a quick response helped contain the fire. Frontier will spend the next day or two conducting a Root Cause Analysis to determine how the explosion happened. Hoflund says it's still to early to know how much damage there was. She thinks they lost the Coker Unit's heater, where the fire was. But she doesn't think that will seriously impair operations at the refinery.