Complex sentence: Ammonia gas is toxic in large concentrations for prolonged periods, and can be fatal, however smelling salts produce only a small amount and there have been no reports of any adverse health problems from their use.
Split into simpler sentences: Ammonia gas is toxic in large concentrations for prolonged periods, and can be fatal. Smelling salts produce only a small amount and there have been no reports of any adverse health problems from their use.