Embalming is considered hazardous to morticians because conventional embalming fluid contains formaldehyde which has been deemed a carcinogen. Long-term exposure to formaldehyde has been linked to myeloid leukemia and other cancers but funeral homes insist it preserves and firms body tissue better than any alternative products. Undertakers are aware of formaldehyde's risks and dangers and consequently take precautions especially by using sophisticated ventilation systems. The air quality is tested periodically to keep formaldehyde air concentrations minimal. Morticians also wear protective clothing, masks, and eyewear. Embalming fluid with 5% formaldehyde is generally injected into the arterial system to replace blood but a 50% solution of formaldehyde is used to fill the body cavity. The average amount of embalming fluid used in a body is three gallons.