An industrial mixer system in a concrete plant is used to produce concrete. Concrete is produced by mixing cement, water, additives and aggregates at high speeds and temperatures to form a liquid composite material that hardens over time. Cement mixers are equipped with hatches that are normally used to clean the inside of the mixer. Such machines are interlocked and each hatch is equipped with a mechanical door lock to ensure that operators and/ or maintenance personnel do not gain access until power to the machine has been disconnected. All interlocks are constructed of a complete stainless steel housing specifically designed for continued operation in difficult, dusty environments.