Captain David Matschke is well aware of the dangers he faces on the job. A firefighter for 32 years, he is trained to race to the scene of house fires, car crashes and even industrial accidents, breaking through windows and doors to evacuate occupants and routinely putting himself in harm’s way. But beyond fire itself, a study published today in the journal Environmental Science & Technology sheds new light on another, more insidious threat that may be putting firefighters’ health at risk: toxic chemicals in smoke.