November 2012, Vol. 24, No.11

Safety Corner

Sewer Rehabilitation: Plan for Safety

Douglas Prentiss

Rehabilitation activities in sewers almost always present workers with potential hazards. Managers, planners, and supervisors can help by adding additional emphasis on safety when performing rehabilitation on the collection system, lift stations, or treatment plants.

Many new and innovative methods for sewer rehabilitation can help limit the number of hazardous tasks performed by workers, but ultimately someone will have to enter parts of the sewer system to perform potentially hazardous work.

 

Risks from new products 

In some cases, new chemicals used to minimize exposure to underground conditions also could introduce new hazards not previously encountered. If new chemicals are being used to repair lines, workers should review the Material Safety Data Sheet (MSDS) for the compounds. For example, for the application of a sealing compound, which uses a new mixture of chemicals, the MSDS will identify the type of personal protective equipment (PPE) needed and the exposure levels at which PPE is needed.

In addition, information on first aid, reactivity to other chemicals, signs of exposure to workers, and many more critical pieces of information are contained on an MSDS and should be reviewed with workers prior to the use of new chemicals.

Many new chemical grouting systems use special equipment that almost completely eliminates worker exposure to the chemical hazards during the sealing of leaks and cracks in the underground pipe. These systems use closed-circuit TV monitoring and remotely operated robotic equipment.

However workers aboveground still mix the grout and operate the high-pressure pumps to allow the entire operation to take place. A simple mixing of incompatible materials by sharing the same scoop and allowing the chemicals to mix has resulted in many fires and releases of toxic gases.

 

Equipment safety 

Many new truck-mounted and portable systems not only have improved the safety of sewer system rehabilitation, but also have eliminated potential hazards associated with their basic operation.

Many new jet trucks have multiple capabilities and are a primary tool for sewer rehabilitation. However, simply backing a jet truck toward an overflowing manhole poses several serious hazards and requires a well-trained and safety-conscious operator. This begins with having a properly licensed operator with a commercial driver’s license and the necessary endorsements. The driver also needs to be properly trained on the all aspects of the equipment and be aware that the area near the overflowing manhole may have a void beneath the pavement. Many jet trucks have backed over manholes only to have the road collapse under the weight of the truck.

 

Special hazards 

Supervisors must review with all workers the special issues relating to parts of the sewer system undergoing rehabilitation work. Communications dispatch centers and call-out personnel also may need to be made aware of any special hazards posed by the interim condition of the sewer system awaiting rehabilitation or any special conditions created during rehabilitation.

For example, a wide range of basic rehabilitation operations require around-the-clock pump-watch-type activities for short periods. Once again, basic safety must be heightened for workers monitoring the pumping operation. Not only must workers be kept safe, but the importance of the pumping function also must been clearly explained to those onsite.

These workers must be well-informed and able to take prompt corrective action to ensure not only their safety but also continuation of the process. An important part of this training is to identify and put in place a realistic contingency plan for the workers prior to the work taking place. Pumps used during rehabilitation must be designed to meet the expected flows, and consideration for a backup pump is part of a basic rehabilitation plan.

 

Time of day (or night) concerns 

It is not unusual for critical activities surrounding rehabilitation projects — such as a tying in or taking out a section of main line — are done late at night when flows are low. However, these same off-hours may pose additional hazards for workers.

Uneven walking and working surfaces are common around wastewater collection field activities. Slip and fall hazards are made worse in diminished light. Managers and supervisors should remind workers of the additional hazards, provide additional lighting (where possible), and carefully monitor worker access around the hazardous areas.

 

Trenches and confined spaces 

Since much rehabilitation work happens below ground, trenches often become one of the main hazards workers face. Trench safety must be monitored by someone trained in excavation safety.

Heavy equipment needs to be used properly and safely. For example, the depth or reach of a digging machine is an important consideration and is critical for excavation safety. The proper equipment used properly prevents hazards and accidents.

In addition to crush and engulfment hazards, trenches and excavations also can contain the same hazardous atmospheres found in collection systems. Flammable, toxic, and oxygen-deficient atmospheres can exist in any excavation. Excavations for existing sewer infrastructure have a real probability that a hazardous atmosphere has existed at one time or does exist now. The Occupational Safety and Health Administration (OSHA) Trench and Excavation Standard (29 CFR 1926.650) includes requirements for atmospheric monitoring similar to the confined space requirements.

Many confined space standards also apply to trench and excavation operations. Rehabilitation of collection lines, lift stations, air-relief pits, treatment plants, or any other sewer-related facility require reviewing and adhering to OSHA’s confined space standard, CFR 1910.146 Appendix E, Sewer System Entry.

Everyone who reads a safety article probably has a basic understanding of OSHA’s permit-required confined space standards, but not many have actually read Appendix E about sewer entries. Appendix E is a letter from OSHA to the wastewater industry; OSHA is very clear in what it thinks the industry should be doing.

The trench and excavation and confined space standards are tied together with worker safety as the common goal. All wastewater professionals should read and learn both of them.

 

Working with contractors 

In some cases, rehabilitation is too costly or dangerous to perform in-house and requires hiring a subcontractor. However, the system owner still has safety responsibilities during confined space work. Review OSHA’s Contractor Requirements (CFR 1910.146 [c][8]) to ensure the sewer rehabilitation specialist meets all required safety and worker training requirements.

Ultimately, the decision to use in-house labor or contractors is an individual organization’s decision, but it’s always better made in advance of the need. Monitoring the collection system and performing preventive maintenance not only helps to avoid dangerous situations, but also helps to keep rehabilitation costs in check.

 

Douglas Prentiss is president of Doug Prentiss Inc. (Alachua, Fla.).