40% alcohol by volume is 70 degrees proof spirit in UK, or 80 degrees proof spirit in USA. This is the most common strength in UK, higher strengths are available. This will easily light, as I demonstrate every Christmas.
Some expensive 'cask strength' whiskys are around 57% alcohol by volume (49% by weight), 100 degrees proof spirit in UK or 114 degrees proof spirit in USA. The three different measures are a source of confusion. If you are accustomed to seeing it sold as so many degrees proof and you see it quoted as percentage alcohol you may be under the impression it is a weaker product than what you usually drink.
So you can light a fire with 40% alcohol, or get dangerously drunk on 13% wine - if flight attendants don't stop you.