Learn Portuguese (Portugal): Deves usar o capacete enquanto estás na obra. - You must wear the helmet while you are at the construction site.

The word enquanto means 'while'. It introduces a time-related phrase that happens at the exact same time as the main action. Because both actions are real facts in the present, we just use the normal present tense for both verbs (deves and estás).

Doesn't usar mean 'to use'? Why is it translated as 'to wear'?

In Portuguese, the verb usar is used for both using a tool and wearing an item. While there is a specific verb for putting on clothes (vestir), you always use usar for accessories like a helmet (o capacete), hats, glasses, or jewelry.

Why do we say na obra instead of just em obra?

Na is a combination of the preposition em (in/at) and the feminine word for 'the' (a). In Portuguese, specific locations like this almost always need 'the' before them, so 'at the construction site' becomes em + a = na obra.

Could I say Tens de usar instead of Deves usar?

Yes! Tens de usar (you have to wear) sounds like a strict, mandatory rule. Deves usar (you must or should wear) is also a strong obligation, but sounds slightly more like a serious safety recommendation or moral duty. Both are very common and natural here.