That's an interesting question. I don't know the answer, but I can share the observation that in the Masoretic Hebrew bible there are 17 occurrences of the word "and fire" (ואשׁ). 15 times the vowel pointing is "וְשׁ" and twice the vowel pointing is "וָשׁ". Both vowel pointings seem permissible, but I don't know how to make that vowel pointing decision? It's been a year since you asked your good question, let's hope someone can come along and take us further on this question.
Thank you for your research. I would have thought this combination to be more common in Biblical language than just גָּפְרִית וָאֵשׁ Gen 19.24 sulphur and fire and דָּם וָאֵשׁ Joel 3.3 blood and fire, but looking closer at all the other passages, and fire is not closely knit to a preceeding noun forming to a pair, but begins something new syntactically with disjunctive cantillation signs like יוֹמָם וְאֵ֕שׁ Ex 40.38 by day, and there was fire.
Thanks to your comments, now you have me doing more research on this! I think there is a pattern concerning the conjunctive and disjunctive accents to help figure out these vowel choices for "and fire" (ואשׁ). There seems to be a pattern concerning the adjacent Hebrew word that immediately proceeds the Hebrew word "and fire" (ואשׁ). The Hebrew words that immediately proceed "and fire" are disjunctive accents of various kinds, which results in the vowel pointing of "וְאֵשׁ", while the Hebrew word that proceeds "and fire" in Gen 19:24 and Joel 3:3 are each identified with a conjunctive accent (that is called "מוּנַח" = ֣ ). See the accents in Gen. 19:24 (גָּפְרִ֣ית) and Joel 3:3 (דָּ֣ם). Notice the common conjunctive accent called "munach" "מוּנַח"( ֣ ) that they each share. Perhaps it is the conjunctive accent immediately proceeding "and fire" that makes it necessary to change the vowel under the letter Vav to a "קָמֶץ" (ָ ). I can't say that I am correct in this, but at least it fits a potentially meaningful pattern in the biblical text. Thanks for your original question and insights.