A driver walked away unscathed after his 18-wheeler caught fire on Everett Turnpike Monday night. According to Merrimack Fire Capt. Jason Marsella, firefighters and state police responded to a tractor-trailer fire on Everett Turnpike southbound near mile marker 15 at approximately 7:04 p.m. Authorities said the 18-wheeler appeared to have an issue with the brakes, which led to the tractor-trailer catching fire.Authorities said the driver pulled over safely and detached the tractor from the trailer. The driver then attempted to extinguish the fire before first responders arrived. However, the tractor-trailer carrying a load of peat moss was quickly engulfed in flames and crews stepped in to help.Marsella said firefighters were able to extinguish the fire soon after it started. The driver was not injured.The name of the driver has not been released.