The chemicals used in the launch of spacecraft can pose exceptionally high dangers to human health. Liquid nitrogen and helium can cause asphyxiation.
Liquid oxygen can increase fire hazards by enhancing the inflammability of combustible materials.
Liquid hydrogen readily ignites when it is mixed with air. Of more concern are the hypergolic propellants, so-called because they ignite spontaneously when mixed with a complementary fuel. The chemical formulation for basic hydrazine is N2H4. The vapor is highly irritating to eyes, upper respiratory tract and skin. Liquid coming in contact with the eye may cause permanent corneal lesions and severe exposure may result in temporary blindness.