Latin had two uses of the prefix in-. One was a negation (as in ineligible) and the other was an intensifier derived from the Latin preposition in (which just happens to be the same as in English). The two uses rarely clash, but people often misunderstand the intensive aspect of inflammable for the negation. So better to just say flammable and maybe save someone’s life from a fiery death.
Latin had two uses of the prefix in-. One was a negation (as in ineligible) and the other was an intensifier derived from the Latin preposition in (which just happens to be the same as in English). The two uses rarely clash, but people often misunderstand the intensive aspect of inflammable for the negation. So better to just say flammable and maybe save someone’s life from a fiery death.