The size of the particles in question tends to influence the toxicity of the fumes, with smaller particles presenting greater danger. Additionally, many processes produce fumes and various gases, most commonly carbon dioxide and ozone, that can prove dangerous if ventilation is inadequate. Furthermore, because the use of compressed gases and flames in many welding processes pose an explosion and fire risk, some common precautions include limiting the amount of oxygen in the air and keeping combustible materials away from the workplace.[3] Welders with expertise in welding pressurized vessels, including submarine hulls, industrial boilers, and power plant heat exchangers and boilers, are generally referred to as boilermakers.[5]