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The heat is on

The summer of 2024 has passed after logging some extremely hot days. Thanks to a changing climate with an apparent tendency toward more extreme heat events, the summer of 2025 could match 2024’s extreme heat records, and possibly beat them.

Working in extreme heat can be dangerous for anyone working outdoors, but it comes with an extra risk for manure applicators. Here’s what the dangers are, and how to beat them.

An odoriferous danger

The aroma that goes along with manure application is more than just a nuisance; it’s a potentially deadly odoriferous danger. One of the reasons is hydrogen sulfide along with other gases that can displace breathable oxygen. Hydrogen sulfide gas is emitted by decomposing manure. It is released whenever solid or liquid manure is agitated or moved, and is toxic to breathe.

“Hydrogen sulfide is produced by the action of certain bacteria, and obviously, as temperatures increase, bacterial action really speeds up,” says John Shutske, professor and agricultural safety and health specialist at University of Wisconsin-Madison. “Think of leaving a sandwich or other food product on the counter or picnic table in 85-degree weather versus 45-degree: Which will lead to faster bacterial spoilage? The same is true with respect to bacterial action in stored manure: As temperatures increase, some of the hydrogen sulfide and other gases produced by bacterial action escape to the ambient air. And when you begin to pump, agitate, and stir it up, it’s just like shaking a can of soda – the gases within are rapidly released. The effect is often magnified if the stored manure is crusted, because even more gas can be trapped in the liquid slurry to be released suddenly.”

Walter Grose is president of Husky Farm Equipment in Alma, Ontario and also serves as a safety advocate, including as secretary with the Wellington County Farm and Home Safety Association. In addition to being toxic, “hydrogen sulfide usually stays close to the ground because it’s heavier than air,” says Grose. “However, when you’re pumping out liquid manure and hauling it on the field, you’re doing a lot of mixing and stirring. This causes some of the hydrogen sulfide to escape as you apply the liquid manure, rising up into your breathing area. If you breathe it in, you’ll suffer anything from a headache to unconsciousness and even death, depending on the concentration of hydrogen sulfide in the air around you.”

Donning a typical “air purifying” respirator won’t protect you from hydrogen sulfide or manure gases. However, a gas detection monitor can warn you of its presence. 

“The monitors I recommend in the U.S., usually will have an audible alarm that will go off at the permissible exposure limit (PEL) of 10 parts per million (ppm),” says Shutske. “Ten ppm is high considering that the maximum short term exposure limit is only five ppm, and working for a full day at levels over one ppm is considered to be a threat to human health. Exposure at levels as low as two ppm will lead to headaches, nausea and significant respiratory problems with people who have asthma. Levels of 100 ppm or higher are considered immediately dangerous to life and health. Hydrogen sulfide is tricky because at those higher levels, the gas deadens your sense of smell, which means people who die often are no longer smelling the gas. At higher levels, a person no longer able to smell the noxious rotten egg odor might take a couple breaths that will result in rapid unconsciousness and death.” 

How heat factors in

Beyond the dangers of hydrogen sulfide, manure applicators face the same health-related risks as anyone working outdoors in extreme hot conditions. “The heat produced by your body while working plus high outdoor temperatures makes it more likely for your body to overheat,” says Dr. Laurel Harduar Morano, associate professor at Michigan State University. “In addition to the weather, other factors that may increase the body’s likelihood of overheating include the amount of clothing a person is wearing, such as the personal protective equipment (PPE) used to keep a person safe; the workload, such as pushing a heavy wheelbarrow; prior heat-related illness, sun burns, certain medications, obesity and chronic conditions such as cardiovascular disease or diabetes, make it harder for the body to maintain the correct temperature.”

There are many medical conditions that are caused by overheating, the most dangerous of which is heat stroke. “If symptoms of heat stroke occur in someone such as confusion, slurred speech, fainting, nausea/vomiting, rapid pulse, seizures, hot dry skin or heavy sweating, call 911 immediately, then move the person to a cool place and help lower their temperature with a cool wet cloth and/or cool bath,” says Morano. “Remove any extra clothes such as shoes, socks, or PPE and do not leave the person alone. Ice, cold towels, or fans can be used to cool the individual by being placed on the person’s head, neck, face, armpits, and groin area. Individuals can also wash their head and neck with cool water.”

Other illnesses to watch out for: 

• Heat exhaustion symptoms include fatigue, irritability, thirst, dizziness, lightheadedness or heavy sweating. It can be treated the same way as heat stroke. 
• Heat rash presents as clusters of red bumps on the skin, usually on the neck, upper chest and skin folds. It is treated by keeping the affected area dry – don’t apply ointments or creams. 
• Heat cramps are muscle spasms or pain usually taking place in the patient’s legs, arms, or the trunk. Treat heat cramps by having them drink water – eight ounces every two minutes – and eating a snack. 
• Heat syncope symptoms are fainting or dizziness. Treat by having the affected person sit or lie down. Have them slowly drink fluids. 
• Rhabdomyolysis, often called rhabdo, is a medical condition associated with heat stress and prolonged physical exertion. Rhabdo causes the rapid breakdown, rupture, and death of muscle. When muscle tissue dies, electrolytes and large proteins are released into the bloodstream. This can cause irregular heart rhythms, seizures, and damage to the kidneys. “Anyone can get rhabdo, even people in great shape,” says Morano. “Dehydration doesn’t cause it but does make it worse. To treat rhabdo, stop activity, drink liquids such as water, and seek immediate medical care – ask to be checked for rhabdo.”

Heat stress can also cause many issues that impact the safety and well-being of individuals. With heat and fatigue can come distraction – forgetting to take key safety precautions and doing important steps “out of order” such as not turning off equipment before unhooking a piece of equipment or hose connection, or chocking the wheels of a tractor parked next to a lagoon. 

Preventative measures

There are many preventive measures that manure applicators can take to protect themselves during extreme heat. Avoiding heat is “not always practical,” sayd Shutske, “and thankfully in most cases, ‘application’ will be done in a vehicle or tractor with a cab and AC. Cabs with AC will increase comfort and reduce dust exposure leading to less fatigue.”

Even in ideal locations – at the edge or corner of a lagoon, with a good breeze blowing manure away, “Having a monitor with the pumping crew is important. In situations where you are pumping from a corner or side of a storage structure and the wind is blowing right toward the pump out staff, either consider moving the equipment if possible or waiting for a change in wind direction.”

Meanwhile, drink plenty of fluids; take frequent breaks in the shade and, if possible, reschedule high-energy tasks for earlier or later in the day, says Morano. As temperature and humidity rise, so should the number of breaks. One last tip: “Use the buddy system,” says Morano. “Often it is a coworker who first notices signs of heat stress in another worker.” •

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