If you blow on a spark, it will glow; if you spit on it, it will be put out; and both come out of your mouth: A spark is the smallest beginning of what could become a fire. While it is still a spark, you can easily put it out. But you can also help it grow into flames. Ben Sira is simply saying that you blow with your mouth (to make a fire) and you spit with your mouth (to put out the spark). His meaning, of course, is that a person’s words can take a small conflict and make a big argument out of it, or end the conflict completely. It is permissible for translators to make this meaning clear as Contemporary English Version does:

• Blow on a spark
and it bursts into flames;
spit on a spark
and it dies out.
In the same way, your words
can either heat up an argument
or make it cool down.

Quoted with permission from Bullard, Roger A. and Hatton, Howard A. A Handbook on Sirach. (UBS Helps for Translators). New York: UBS, 2008. For this and other handbooks for translators see here.