I guess its worth looking at a material safety data sheet and ask yourself.
Here is a link to one in the UK: https://www.flints.co.uk/pdffiles/isopropyl_alcohol_msds.pdf
And one in the USA: https://monumentchemical.com/uploads/files/SDS/IPA%20-%20SDS.pdf
and in Canada: https://www.fishersci.ca/shop/msdsproxy?productName=A426P4&productDescription=2-propanol-histological-fisher-chemical-5
Some interesting points from both:
Vapours may irritate the respiratory system and cause coughing, asthmatic breathing and breathlessness. Prolonged inhalation of high
concentrations may damage respiratory system. Central nervous system depression. Vapours may cause headache, fatigue, dizziness and nausea.
UNUSUAL FIRE & EXPLOSION HAZARDS
Heat may cause the containers to explode. Solvent vapours may form explosive mixtures with air. May travel considerable distance to
source of ignition and flash back. May ignite at high temperature. Vapours are heavier than air and may spread near ground to sources of
My own thoughts are that if someone wants to ignore the safety data sheet and they get away without any accidents then good luck to them - But its their own risk!! BTW - In Canada its classified as a hazardous substance (See extract below)
Just as a footnote - You need a minimum of 2% in air to form an explosive mixture, but that should not be confused with the amount to flash ignite, its got a flash point of only 12c so any sparks near it may ignite it
This article makes interesting reading: https://www.ccohs.ca/oshanswers/chemicals/flammable/flam.html