Farm Respiratory Hazards

Farmer’s Lung and Organic Dust Toxicity Syndrome (ODTS) are names given to two farm occupational diseases caused by inhaling airborne mold spores.
Farm Respiratory Hazards - Articles


Many people associate farming with fresh air and a healthy, robust environment where farmers work and live. However, farming is filled with respiratory hazards: pesticide vapors, dusty fields, dangerous hydrogen sulfide accumulations in manure pits and pump sumps, nitrogen dioxide in conventional silos, and many other things. Farmer's Lung, organic dust toxicity syndrome (ODTS), and silo fillers's disease are three occupational diseases associated with production agriculture. Asthma continues to emerge as an ongoing respiratory illness for many farmers.

One of the main culprits in respiratory illnesses for farmers is mold spores. Mold spores are produced by microorganisms which grow on living plants and on baled hay, stored grain, or silage with high moisture content (30 percent). These microorganisms become active when temperatures reach 70 degrees Fahrenheit in poorly ventilated areas. Farmers typically contract these diseases in the winter and early spring because the mold has had time to develop in closed storage areas and the crop is being removed from storage.

Heavy concentrations of mold spores appear as a dry, white or grey powder in grain or forage. When the feed is moved, billions of these microscopic sized particles become airborne and attach themselves to dust. The particles pass through the body's natural filtering mechanisms (e.g., nose, hair, and throat mucous) and accumulate in the lungs where they can cause an allergenic type of pneumonia. Repeated attacks can lead to scarring of lung tissue which impairs its function and can cause permanent damage.

Farmer's Lung

Farmer's Lung can also be referred to as farmer's hypersensitivity pneumonitis (FHP) and is a noninfectious allergic disease that affects normal lung function. This condition is a result of inhaling mold spores from baled hay, stored grain, or silage with high moisture content (30%). These mold spores are so minuscule that about 250,000 of them can fit on the head of a pin so a person could easily breathe in millions of them in just a few minutes. Once they are inhaled, these tiny mold spores easily move into the lower part of the lungs causing symptoms to appear within four to six hours. Exposure to mold spores may produce the following symptoms: First, there is a delayed reaction of 3 to 8 hours during which the patient may develop shortness of breath; tightness in the chest; fatigue; a dry, unproductive cough; muscle ache, headache, chills and fever. The most serious stage of the reaction may last approximately 12 to 48 hours, but some effects are likely to linger for up to two weeks. Acute exposure symptoms eventually disappear with no apparent lasting effect, particularly with first time or mild exposures.

A farmer's allergic reaction to these mold spores can be acute, resembling flu or pneumonia or with chronic symptoms similar to a nagging chest cold. If a producer has been diagnosed with Farmer's Lung, they should avoid any additional exposure to mold spores to reduce the risk that their condition could worsen to the point that it could be fatal. A farmer that thinks he or she may have Farmer's Lung should contact their physician immediate to explain their symptoms and the occupational health risk of contracting an agricultural related respiratory illness.

Follow these recommendations to reduce your risk of contracting Farmer's Lung:

  • Identify and reduce the contaminants in your work area.
  • Decrease your exposure to contaminants (e.g., mold spores).
  • Reduce mold spores by using commercially available mold inhibitors.
  • Harvest, bale, store, and ensile grains at the recommended moisture level to reduce mold growth.
  • Examine your feeding system to identify ways to automate feeding to decrease the release of airborne mold spores.
  • Avoid working in dusty places in confined space areas.
  • Ventilate (e.g., fans, exhaust blowers, etc.) to mechanically remove air contaminants.
  • Wear a double strap dust mask or organic dust filter equipped respirator rated at least N95 to reduce your exposure to contaminants.

Organic Dust Toxicity Syndrome

Silo Unloaders Syndrome is another name for organic dust toxicity syndrome (ODTS) because the condition often occurs during the unloading or uncapping of silos. However, other names for this condition include grain fever, toxic alveolitis, or pulmonary mycotoxicosis. Similar diseases associated with other agricultural occupations have been termed Bird Fanciers' Lung, Mushroom Workers' Lung, and Wood Pulp Workers' Disease.

ODTS is caused by exposure to large amounts of organic dust. Some areas on the farm that may have high dust levels include silos, grain storage, hog barns, and poultry barns. This disease can display symptoms approximately four to six hours after exposure. Symptoms include cough, fever, chills, fatigue, muscle pain, and loss of appetite. ODTS and Farmer's Lung are both similar in routes of entry and symptoms. Since the symptoms of Farmer's Lung and ODTS are often similar to other health conditions (e.g., pneumonia, flu, etc), the diseases are often unrecognized by farmers and family members and misdiagnosed by physicians not familiar with agricultural health hazards.

To reduce your risk of contracting ODTS, follow the same recommendations for the prevention of Farmer's Lung. Wear a respirator to reduce your exposure to organic dust. Implement best management practices to maintain good air quality in confinement buildings used for swine and poultry and always wear the appropriate respiratory protective equipment.

Silo Filler's Disease

Silo Filler's Disease occurs when a person inhales nitrogen dioxide, which is a gas produced during the fermentation of silage. The primary danger of this disease is that the person exposed to this silo gas may not experience symptoms even though lung damage has already occurred. For example, fluid can build up in a person's lungs up to 12 hours after they have been exposed to nitrogen dioxide.

The National Institute for Occupational Safety and Health (NIOSH) has designated 20 ppm as a moderate level exposure called 'immediately dangerous to life and health (IDLH). At this level, a farmer can have the following symptoms: cough, hemoptysis (coughing up blood), shortness of breath, and chest pain. At a higher level of 100 ppm, the farmer may experience pulmonary edema (fluid in the lungs) and swelling in the lungs leading to long-term respiratory problems or death. Lower concentrations (15 to 20 ppm) are still considered dangerous and can result in a respiratory impairment. Immediately seek medical attention if you have been exposed to any level of silo gas.

Follow these recommendations to reduce your risk of contracting Silo Filler's Disease:

  • Never enter the silo during the first 2 - 3 days after filling.
  • If entry is required after day 3, ventilate the silo and all adjacent areas by running the silo blower for 15 to 20 minutes before and during entry.
  • Use a portable gas monitor to monitor the gas and oxygen levels in the silo.
  • Always have at least two people outside of the silo that you can visually communicate with at all times.
  • Wear a harness that is attached to a life line and secure anchor point.
  • Wear a N95 rated dust mask if entering the silo after the three week post-filling period.
  • If entry is completely unavoidable during the three week period, wear a self-contained breathing apparatus.


Of growing concern is the high incidence of asthma in all age groups and occupations. Typically, asthma includes airflow obstruction, bronchial hyper-responsiveness, and chronic inflammation of the airways which can cause wheezing, shortness of breath, coughing, and tightness in your chest. Asthma is typically classified into two types including allergic or non-allergic. Allergic asthma or atopic is caused by exposure to an allergen (e.g., pollen, pet dander, mold, etc.). Non-allergic asthma is caused by exposure to non-allergic substances (e.g., grain dust, cleaners, wood smoke, etc.). Asthma types can be broken into additional categories that include occupational, viral induced, nocturnal, and Reactive Airway Dysfunction Syndrome (SADS).

Follow these recommendations to reduce your risk of triggering an asthma attack:

  • Store grain at recommended moisture content levels to reduce the growth of mold spores.
  • Ventilate animal housing areas to decrease the accumulation of ammonia and other gases.
  • Frequently remove animal waste from the barn to decrease ammonia build-up and reduce exposure to urine and fecal allergens.
  • Identify high dust hazards around the farmstead and reduce dust exposure by cleaning these areas.
  • When cleaning a barn or stable, lightly water areas to reduce the risk for airborne dust.
  • Wear a NIOSH approved and properly fitted N-95 or N-100 disposable particulate respirator when completing work tasks (e.g., cleaning, harvesting, grain handling, etc.) to protect yourself from dust, bacteria, fungi, insects, and animal products.


Respirators can prevent these types of respiratory ailments related to production agriculture - but only if you wear one! Make sure you choose the right type of respirator for the hazard(s) you will encounter. Before long, wearing a respirator will become a habit.


Asthma and agriculture. (2012). Farm and Ranch eXtension in Safety and Health (FReSH) Community of Practice.

Written by: Dennis J. Murphy, Distinguished Professor