Well no, minimal isn't what you want to look at it as..
Think of all the people you have seen torch bowls. Do you think that butane is just dissipating before it hits the nug? It's being literally bathed over it
Think of all the bowls you have hit by yourself and you just can't get it to light by using your bic, causing you to constantly hit the emit fumes button and you eventually inhale that 'tane...
notice the back of your throat if you were to go and smoke a bowl with a tane lighter.... on my body, my throat got this itchy tingling feeling if I used a bic lighter... went out to my lhs and bought a spool of hemp wick
Just think of all the times you've ever used a butane lighter to light your nug, and add those up together and just imagine capturing all the butane that eventually got down your pipe and condense it into one giant container over your smoking career, essentially, this is what your inhaling, just not all at once. Now, some can argue that the body can repair itself by the time anything major happens, but I beg to differ
Inhalation of butane can cause euphoria, drowsiness, narcosis, asphyxia, cardiac arrhythmia, and frostbite which can result in death from asphyxiation and ventricular fibrillation. Butane is the most commonly misused volatile substance in the UK, and was the cause of 52% of "solvent related" deaths in 2000. By spraying butane directly into the throat, the jet of fluid can cool rapidly to –20 °C by expansion, causing prolonged laryngospasm. "Sudden sniffer's death" syndrome, first described by Bass in 1970, is the most common single cause of "solvent related" death, resulting in 55% of known fatal cases.