"Hard hats must be worn at all times"

I'm a Engilish-Japanese translator.
Please tell me the meaning of the following phrase: "Hard hats must be worn at all times".

Hard hat here>
must
worn
must be worn
at all times

あなたのヘルメットをいつも身に着けなさい
あなたのヘルメットをいつも身に着けなければならない

It comes from the 安全第一 information campaign for construction sites, meaning "You always must wear a very hard plastic yellow hat for safety."