Muskegon firefighters are crediting a broken water pipe for putting out an explosive fire at a licensed medical marijuana grow operation.Firefighters were called to the commercial facility at 181 South Getty Street shortly before 8 a.m. Wednesday. 24 Hour News 8 reports, by the time they arrived, the fire was extinguished.Investigators believe a refrigerator motor ignited butane that a 35-year-old assistant was using to make suspected butane hash oil. The site’s garage tenant discovered the fire and called 911.The fire caused an estimated $60,000 to $70,000 in damage to the building, mostly to its electrical system.The incident remains under investigation.