The major cause of injuries is slips and falls. Tools, parts, and other things should not be left lying around. Grease droppings, oil, sludge, and especially polymers should be cleaned up as soon as possible. Warning signs, railings, and covers in place can protect against low piping, open tanks, and open manholes or hatches. The simple knowledge of proper lifting techniques, bending the knees and lifting with muscles of the legs, can save many strained or injured backs.

For work in manholes in streets, safety requires full protective measures from traffic hazards as well as from the hazards of explosive gases, hydrogen sulfide, or the lack of oxygen in the manhole or sewer. Warning signs and barricades should be set up at suitable distances on each side of the manhole. On busy streets, it may be desirable to station workers to flag down and detour fast-moving vehicles. On wide, multi-lane streets, the service truck can be stationed on the side of the manhole toward on-coming traffic. It is important that sufficient workers be provided for the job at hand. There should be at least two workers at the top when one goes below. A cage or guard device around the manhole adds protection and aids entering and leaving the ventilation hole or lifting notch. When lifting a manhole cover, a pick-axe may slip and cause injury or, if struck hard, may give off an igniting spark. Unless a cover is very heavy, it is safer for one person to handle it alone.

Before entering a manhole, the confined atmosphere should always be tested for the presence of explosive gases, hydrogen sulfide, and oxygen deficiency. After determining that the conditions are safe for entry, positive forced air ventilation should be started and operated continually whenever a worker is in the manhole or sewer. There should also be a continuous sampling of the atmosphere with a visual signal alarm device kept near the worker.

Before descending into a manhole, note should be taken of the width, spacing, and arrangement of manhole rungs and, if they are staggered, particular care must be taken to get started with the proper foot and to avoid falling. Steel rungs may lose their galvanizing and become dangerously corroded. Each rung should be tested during descent while the worker distributes weight evenly between feet and arms. A safer means of entry would be to use a manhole ladder, which can be carried on the service truck. The ladder should extend about three feet above the street surface as the worker climbs down. Even with a separate manhole ladder, the worker should use caution as his or her boots may have oil on the soles, causing a fall.

On small sewers, no one should enter a manhole deeper than the height of the chin without wearing an approved parachute-type safety harness with rope attached. In an emergency, when a safety belt may not be at hand, a stout rope tied snugly under the arms with a bowline or other non-slip knot may be the means of saving a life. In either case, at least two people should be a the top of a manhole at all times when a third worker is inside in order to handle the life line and help the worker if necessary. A safety harness should also be worn when entering any enclosed spaces around a sewage treatment plant, such as pump suction wells, empty digestion tanks, sludge storage wells or any other space where access is difficult and assistance may be needed to climb out.