Negative conditions (à moins de)

When outlining strict safety protocols—like those for underground caving (la spéléologie)—you will often need to state what will happen unless a precaution is taken.

With an Infinitive

To express a negative condition ("unless"), use à moins de followed by an infinitive. This structure works when both actions share the same subject, or when stating a general rule.

The helmet is mandatory in caving, unless you stay outside.
Le casque est obligatoire en spéléologie, à moins de rester dehors.
You are going to fall into the chasm, unless you secure your harness.
Tu vas tomber dans le gouffre, à moins de fixer ton baudrier.

As always, de contracts to d' before a vowel or silent h.

Do not venture into this cave, unless you are very experienced.
Ne t'aventure pas dans cette grotte, à moins d'être très expérimenté.

With a Noun

You can also place a noun directly after à moins de to mean "unless there is" or "barring" a specific event.

We are about to go down, unless there is a problem.
Nous sommes sur le point de descendre, à moins d'un problème.