Currently, achievements involving Extinguisher and Chem Spray are pretty much the same thing -- "Extinguish X fires with Y tool" (with Chem Spray being a bit tougher because it only extinguishes 3 stacks of fire at a time). To make things more interesting and bring more focus to what makes Chem Spray not just a "weaker Extinguisher with some post-use preventative effect," let's change the achievement requirements to something geared more towards its purpose like:
"Prevent X fires with Chemical Spray"
(This counts the fire stacks that would have inflicted a sprayed component if it had not been sprayed.)
This way, newer players may learn to be more proactive in their Chem Spray usage, especially now that extinguishing isn't possible during tool cooldowns. Instead of only using the tool to extinguish fires after they happen, they may begin to realize the benefits of spraying components briefly before combat starts and sometimes choosing Chem Spray over Extinguisher depending on opponents' loadouts/strategies.
For reference, the current achievements for Engineer involving Chem Spray are the following three:
Fixin' 11 -- Chemical Welfare [sic] (<--By the way, should this be "Warfare"? Or is it to imply that spraying aids the ship's wellness?)
Extinguish 200 fires on hull with Chemical Spray
Rebuild 200 guns
Teamwork 2 -- Fireproof
Extinguish 20 fires on guns with Chemical Spray
Experience 3 -- Dowsed
Extinguish 100 fires with Chemical Spray