manlock

A manlock is a small sealed chamber that allows workers to enter or exit a pressurized work environment while maintaining the pressure differential. It functions as a transitional airlock, typically cylindrical or rectangular, with two doors: an outer door opening to atmosphere and an inner door opening to the pressurized zone. The worker enters through the outer door, the outer door seals, air is pumped in to match the pressure inside the working chamber, then the inner door opens to allow entry. On exit, the process reverses, allowing the worker to decompress safely.

Manlocks are essential in mining, caisson work, and tunnel boring where ground conditions or construction methods require compressed air to hold back water or unstable ground. The chamber itself is typically steel, ranges from 4 to 8 feet in length, and has internal diameters of 3 to 5 feet depending on site requirements. A typical manlock will have pressure gauge ports, air supply lines, and relief valves to prevent dangerous overpressurization during the transition.

Decompression and safety

The critical function of a manlock is managing decompression sickness (the bends) in workers exposed to elevated pressure. A worker in a caisson working at 30 pounds per square inch gauge (about 2 atmospheres) must decompress in steps rather than immediately returning to atmospheric pressure; the manlock provides this controlled transition. Decompression schedules are based on depth, duration of exposure, and regulatory standards. Rapid pressure changes can force nitrogen bubbles to form in blood and tissues, causing pain, paralysis, or death.

The term 'manlock' distinguishes this worker-scale airlock from the larger 'material lock' or 'muck lock' used to move equipment and spoil out of the pressurized chamber. In modern tunnel boring machine (TBM) operations, the manlock is built into the machine shield and allows workers to access the cutting face for inspection and emergency repairs without depressurizing the entire working chamber. Modern installations often include electric hoists, communication systems, and dual-door interlocks to prevent both doors being open simultaneously.

Regulatory bodies including OSHA and various national mining codes specify manlock dimensions, pressure ratings, inspection intervals, and the presence of a lock tender or authorized attendant during all transitions. Failures, stuck doors, air leaks, gauge malfunctions, have caused accidents; periodic hydrostatic testing and certification are required to verify structural integrity and seal reliability.