Blythe:

Acetone is one of the safer industrial solvents. The concentration of acetone in the air needed to make you puke is only 1/10th the amount of the amount needed to start a fire or house explosion. So, with acetone you get dizzy and light headed long before there's any real risk of a fire or explosion.

I've worked with acetone for years, and my best advice is to get him to do his work over the kitchen sink. Acetone will not harm stainless steel nor plastic laminate counter tops. It WILL, however dissolve any acrylic gloss coating put over a marble or granite counter top, and it will dissolve cultured marble, so if you have a cultured marble vanity in your bathroom, keep him out of there.

Acetone is completely soluble in water, so if you ask him to pour some water down the kitchen sink every few minutes, you'll get rid of the acetone dissolved in the water in your p-trap. Tell him to pour a full gallon down the sink to ensure that any acetone in the p-trap gets past any garburator you have on the kitchen drain piping.

I'd tell him to do his work in your garage, and if he starts daydreaming too much, then to take a breather. But, if that's not feasible, tell him to work over the kitchen sink if you have a plastic laminate counter top. Acetone won't harm a stainless steel kitchen sink or a plastic laminate counter top. And, leaving the kitchen ceiling fan on while he's working will provide the needed ventilation.

Acetone is used by itself, or mixed with amyl acetate (also called "banana oil") to make nail polish remover.

You don't need to know the rest:

Newbies often think that acetone and methyl ethyl ketone are completely different solvents because they have a different name. In fact, they're chemical cousins. Both acetone and methyl ethyl ketone belong to a chemcial family of solvents called "ketones". Every ketone has the general formula:

A
|
C=O
|
B

If A and B are both methyl groups (-CH3) then that chemical is called di-methyl ketone, or acetone for short.

If A is a methyl group and B is an ethyl group (-CH2-CH3) then it's called methyl ethyl ketone, or MEK for short.

So, if this guy is using acetone to remove the lettering on his plastic pipes, most likely MEK will work equally well, and because it's a larger molecule, evaporate less rapidly. Tell him to use MEK instead so that there's less solvent vapours inside your house.

And, I can't see why he can't do this in the garage where he's out of the wind and the smell isn't gonna stink up the house.