The smokebox (or front end) is an extension of the boiler shell where the heated exhaust gases are drawn from between the tubes and flues. A chamber is created by the forward (or front) tube sheet which divides the water space from the smokebox. The blast pipe's exhaust-steam nozzle creates a partial vacuum in this chamber, pulling combustion gases forward and then forcing them out the smokestack. The smokebox may also contain a series of baffles and screens to trap sparks—as well as inducing additional heat to saturate the steam.