As debates about global warming get more intense and energy prices climb, there is growing interest in the advantages of geothermal energy. Such energy involves using heat generated by the Earth itself to condition spaces and generate electricity. While geothermal energy has not caught on in a big way in most parts of the U.S., workers are more likely to encounter projects in the next several years.Geothermal energy is not a single approach. Instead, it describes a wide variety of technologies taking advantage of local conditions in an equally wide variety of ways. That can range from geothermal heat pumps that heat and cool homes and small commercial buildings to massive power plants that tap into the same energy that powers the famed Old Faithful geyser in Yellowstone National Park.

No matter the size or scope, geothermal energy systems convert heat within the Earth into energy that can be used by earth’s residents. Whether it involves the year-round temperatures of dirt and rocks below the frost line, or the intense energy produced by the planet’s fiery core, geothermal energy transforms those temperatures into useful and predictable levels.

Geothermal heat pumps are based on the same heat-transfer concepts at the heart of the air-source heat pumps installed in tens of millions of homes, small businesses, and government facilities. Most use one or more loops of pipe installed below the frost line. Water or a mix of water and glycol or saline are circulated through these pipes to a heat exchanger. Throughout much of the U.S., the ground below the frostline stays at a fairly steady temperature all year long, balancing the air temperature with the heat created at the Earth’s core. Generally, that ground stays between 50 and 70 degrees Fahrenheit year ‘round.

During the winter months, geothermal heat pumps use the warmer temperatures underground to heat indoor air to comfortable levels. During warm weather, they exchange the hot and humid indoor air for the much-cooler temperatures underground.

Geothermal heat pumps are particularly helpful in rural areas that lack access to supplies of natural gas. Buildings in those areas are typically heated with electricity or propane gas, both of which can become costly. In addition, land tends to be more affordable, so buildings are spread out and it’s easy to install underground loops.

Geothermal power plants also use the heat of the Earth to generate energy, but in more powerful and dramatic ways. Many of them capture the steam produced by naturally forming geysers and similar geologic foundations, use it to power turbines linked to electric power generators, and then return it to the Earth. Advantage of this approach over steam generated by fuels such as coal include the lack of combustion that produces pollutants and carbon dioxide gas, and the perception that steam generated from the Earth’s core is limitless.

These power plants gain access to this Earth-generated steam in one of two ways. Some are designed to tap into naturally occurring features such as geysers, capturing the steam that would normally be vented into the atmosphere. Others involve drilling holes into underground rock that spans over sources of steam and piping that to the power plant.

As with any work activity, installing or working around geothermal energy sources can create hazards for workers.

Trenching and Excavating Hazards

Typically, geothermal projects involve trenching or excavating, so fall protection must be considered. OSHA rules regarding open trenches must be followed, and workers who are exposed to potential fall distances of at least 6 feet need to be protected. Safety planning for trenching and excavating must consider the possibility of unstable soils and collapses, both of which may require reinforcement. In addition, when tapping into deep sources for underground steam, there is also the possibility of encountering caves or other underground cavities.

Chemical Hazards

Workers may be exposed to naturally occurring chemicals such as hydrogen sulfide and other chemicals such as ammonia and glycols. If work requires drilling through or cutting concrete, there is the possibility that crystalline silica particles may become airborne. Safety planning should consider all possible chemical exposures, regardless of the source, and provide adequate ventilation and other protection.

Welding and Cutting Hazards

Most geothermal systems use underground metal piping to transport steam or liquids, so workers must be familiar with proper safety practices associated with welding and cutting metal, including appropriate personal protective equipment (PPE).