Silica dust generated by cutting, grinding, or drilling concrete is a serious health hazard. An effective way to reduce worker exposure to respirable crystalline silica is to:

Explanation

Respirable crystalline silica is controlled at the tool: water delivered to the blade or bit, or a shroud with a dust collector and HEPA filter, are the engineering controls the standard specifies task by task, and an employer that follows the specified control for a task is relieved of assessing that task's exposure. Each wrong answer reaches for a lower tier. Respirators alone (b) are PPE, last in the hierarchy, and depend on fit and discipline every hour. Sweeping afterwards (c) arrives too late and re-suspends the dust, which is why dry sweeping is prohibited where a wet or vacuum method is feasible. Compressed air (d) is the worst of the three, because it throws settled dust into everyone's breathing zone, and the standard bars using it to clean surfaces unless it is used with ventilation that captures the cloud.