When you can start smelling chemicals in the air or when the filters have a smell of their own, it's time to change them.
(the filters; have; a smell of their own) (it; 's; time to change them; T:When you can start smelling chemicals in the air or when the filters have a smell of their own) (you; can start; smelling chemicals in the air) Context(you can start,List([5, 18))):(you; can start smelling; chemicals; L:in the air)
you can start,List([5, 18))
the filters it you you
have 's can start can start smelling
a smell of their own
time to change them T:When you can start smelling chemicals in the air or when the filters have a smell of their own
smelling chemicals in the air
chemicals L:in the air