Cleaning parts in the shower?

Yup the Mistress of Metal is giving some good info there.

If you do use silica sand at least wear a proper respirator with at the lowest a P95 or N95 filter but I use a P100 (HEPA) as I'm dealing with mould spores, silica, asbestos and lead particles. And have lots of ventilation to remove the dust if possible.

Silica can be some nasty stuff if you get exposed to enough of it....

Silicosis is a disease caused by the prolonged breathing of crystalline silica dust. Fine particles deposited in the lungs cause thickening and scarring of the lung tissue. Crystalline silica exposure has also been linked to lung cancer.
A worker may develop any of the following three types of silicosis, depending on the concentrations of silica dust and the duration of exposure:

• Chronic silicosis - develops after 10 or more years of exposure to crystalline silica at relatively low concentrations.
• Accelerated silicosis - develops 5 to 10 years after initial exposure to crystalline silica at high concentrations.
• Acute silicosis - symptoms develop anywhere from a few weeks to 4-5 years after exposure to very high concentrations of crystalline silica.

Initially, workers with silicosis may have no symptoms. However, as the disease progresses a worker may experience:

• Shortness of breath
• Severe cough
• Weakness

These symptoms can worsen over time and lead to death.