Keep a safe working pressure.

保持安全工作压力。

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Keep safe working load of derricks.

让吊杆在安全负荷下工作。

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What's the safe working load of each derrick?

每根吊杠的安全工作负荷是多少？

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General ventilation controls should provide a safe working environment.

一般通风调控须足令工作环境安全。

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General ventilation controls should provide a safe working environment.

一般通风调控须足令工作环境安全。

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