Which type of alcohol should never be consumed by humans due to its toxicity?

Methyl alcohol, also known as methanol, is highly toxic to humans and should never be consumed. When methanol is ingested, it is metabolized in the liver to formaldehyde and formic acid, which can lead to severe metabolic acidosis, damage to the optic nerve, and can ultimately result in death. This toxicity is the key reason why methanol is not suitable for human consumption.

In contrast, ethyl alcohol (ethanol) is the type commonly found in alcoholic beverages and is safe for consumption in moderation. Isopropyl alcohol is often used as a disinfectant and, while it is harmful if ingested, its toxicity is different from that of methanol. Butyl alcohol, while also not meant for consumption, does not possess the same level of lethality to humans as methanol. Therefore, the significant danger posed by methanol makes it the correct answer in this context.