As a technology, anaerobic digestion offers many potential environmental and economic benefits for dairy farms. However, anaerobic digestion can pose significant health and safety hazards when not operated properly.

It is important system operators and owners have sound knowledge about the potential hazards facing workers and visitors and take adequate steps to ensure their safety. Regular employee training and good safety practices will not only result in a safer facility but also a more profitable system through reduced downtime and consistent operation.

Anaerobic digestion is intended to optimize the conversion of organic material (dairy manure) to biogas. While biogas is a valuable renewable energy source, the components of biogas – including methane, carbon dioxide and hydrogen sulfide – are dangerous and can be deadly.

Some constituents, such as methane, are colorless and odorless, which can result in unknown exposure. Other components have a pungent odor, such as hydrogen sulfide, but after brief exposure one becomes desensitized.

Common symptoms of biogas exposure are drowsiness, headache, disorientation and respiratory irritation. The severity of the symptoms will depend on the concentration of biogas and length of exposure. Employees should be instructed to exit the digester facility immediately if they begin to feel any of the symptoms of biogas exposure.

While an individual can be exposed to biogas in the general area of a digester, most exposures occur in confined spaces such as storage tanks or buildings. Improper training on confined space entry is a leading cause of accidents related to anaerobic digestion systems.

There are no documented deaths associated with on-farm digesters in the U.S.; however, there have been numerous fatalities linked to manure and feed storages on farms. Under no circumstance should a person enter a confined space, anaerobic digester, manure storage or feed bin without proper training and safety equipment.

In regards to confined space entry, there are far too many examples of unprepared or ill-equipped responders becoming victims. Some basic precautions related to confined space entry that every employee associated with an anaerobic digester should be aware of include:

• When entering a confined area, you should always have another person observing outside the confined area.

• At a minimum, air quality in the confined space should be monitored for oxygen and explosive levels before and during any entry.

• Wear a self-contained breathing apparatus (SCBA).

• Provide a continuous supply of fresh, ventilated air (due to the presence of biogas, an explosion-proof blower should be used).

• Maintain constant conversation with your co-worker so the person can tell if you get into trouble or start acting “funny” while in confined space.

• Wear a harness or safety belt with a lifeline secured to mechanical equipment – such as a winch, hoist or pulley – outside of the pit. Instruct co-workers on its operation.

• Keep ignition sources far away from confined space and sources of biogas.

• Never enter a confined space in which another person is unconscious unless all precautions are taken into account (i.e. buddy system, safety equipment above the precautions of the unconscious person, all other mentioned precautions).

Anaerobic digester operators and owners should receive training on the proper procedures and equipment necessary to enter confined space. Contact the Occupational Safety and Health Administration in your state to learn more about training opportunities in your area.

Other safety concerns associated with anaerobic digesters include the potential for explosion, fire, burns, electrical shock, drowning, falls from elevated platforms and exposure to loud noise. Because digesters utilize “waste” materials as feedstock, there is a potential for exposure to pathogens as well. Proper use of safety signs will alert employees and visitors to potential hazards, significantly reducing the risk of injury.

In addition, basic personal protective equipment should be available and required to be used by all employees and visitors to the digester site. Basic personal protective equipment includes safety glasses, hard hats, steel toe shoes, hearing protection and protective clothing (gloves and laboratory-style jackets).

Additional protective equipment suggested for digester facilities includes multi-gas alarms, fire extinguishers (ABC classification), ring buoy, rigging equipment for fall protection and rescue (harness, lanyard and hoist), hand-held multi-gas detector with extension hose, first-aid kit and explosion-proof safety tools (e.g., flashlight, ventilation blower, and hand tools).

Planning and prevention is the best medicine to avoid accidents and unnecessary downtime. Emergency response to accidents at digester sites should be broken down into the following steps:

1. Assess the extent of risk or danger in the following order:

• Human health
• Environmental health
• Mechanical integrity

2. Correct the problem immediately if possible

3. Contact the appropriate agencies and personnel to resolve the problem

A simple tool to aid with employee training and accident prevention is an Emergency Action Plan (EAP). The EAP is intended as a guide for employees in the event of an emergency, providing necessary information to ensure a safe and timely response to the crisis. Basic information which should be included in the EAP is:

1. Emergency contact phone numbers for the:

• System operator
• Facility manager
• Facility owner
• Local emergency responders (fire, ambulance and police)
• Utility companies affiliated with the digester

2. List of employees trained for emergencies

3. Facility address and exact direction to the digester site from the nearest crossroads

4. Detailed site map showing:

• Electrical service
• Utility disconnects
• Biogas pipelines and shutoff valves
• Location of fire extinguishers and other safety equipment
• Steps to take in specific emergencies

The EAP is intended to be a concise document. A copy of the EAP should be clearly posted at entrance points to the digester facility in order to be readily accessible in the event of an emergency by employees or visitors.

In addition, all equipment manuals should also be maintained in a clearly labeled location at the digester facility. It is suggested that the EAP be reviewed and updated by operators and facility managements a couple of time each year. This ensures the information contained in the EAP is accurate and that employees are familiar with the document and information.

While the safety concerns associated with anaerobic digesters may seem overwhelming, with a little common sense and good employee training, the potential for an accident can be minimized. PD

Safety information contained in the Michigan On-farm Anaerobic Digester Operator Training Course developed by Michigan State University , MSU Extension and the Michigan Department of Agriculture and Rural Development was used as the basis for this article. For more information regarding digester safety or operator training opportunities, please contact Dana Kirk at kirkdana@anr.msu.edu

• Dana Kirk

• Anaerobic Digestion Research and Education Center
• Michigan State University
• Email Dana Kirk