In more than 20 years as a volunteer firefighter, Chief Scott Smith has witnessed some pretty traumatic events and experienced his share of dangerous situations. But nothing like what happened to him and his 5-year-old son on Saturday. Smith said he and son were sitting on the living room couch on Ridge Road in South Brunswick at about 4:30 p.m., when a compact car crashed into the front wall of the house a few feet from them, right where his son had just been playing on the floor. “Where the car hit the house there’s kind of bay window, and there’s a chair right there that he had been playing…