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Manure gas safety – Be aware, be safe

April 11, 2008  by Tony Kryzanowski

At one time, coal miners working underground used canaries to warn them of the presence of toxic gases.

At one time, coal miners working underground used canaries to warn them of the presence of toxic gases. Farm workers and manure haul contractors laboring in confined spaces where similar dangers involving toxic gases exist should be equally mindful of taking precautions to protect themselves against personal injury and even death.

Authors of a study conducted at Purdue University suggest no one should
enter a manure storage container or pit unless absolutely necessary and
farm employees must be instructed never to enter a manure pit to
attempt a rescue without being outfitted with the appropriate equipment
to conduct the rescue, which includes a self-contained breathing
apparatus, or SCBA, similar to those worn by firefighters.

Between 1975 and 2004, 77 people died in the U.S. as a result of being overcome by toxic gases in livestock manure handling or storage facilities, according to a groundbreaking study conducted at Indiana’s Purdue University. There were also 21 documented cases of severe injuries and 14 international fatality cases. While many believed that the greatest number of fatalities occurred within the pork industry, in fact more than half of the fatalities involved dairy operations.

An article summarizing the study’s findings was recently published in the Journal of Agromedicine, produced by the U.S. National Farm Medicine Center. “In my opinion, there is never any good reason for anyone to enter a manure storage pit,” says study and article co-author, Dr. William E. Field, yet he knows that in practical terms it will happen. He co-authored the study with Randy L. Beaver.


What Field would like workers to consider before they enter a manure pit is whether that piglet or broom stick that has fallen into the manure pit is worth the potential for permanent brain damage or the loss of life. Hydrogen sulfide, methane, carbon dioxide and ammonia pose a significant risk that can be avoided through properly designed manure handling facilities, properly ventilated intensive livestock structures, safety gear like portable air quality monitoring devices, signage in areas warning individuals about the potential danger of asphyxiation, installing fences to restrict access to dangerous sites and in extreme cases, using respirators to avoid asphyxiation. The cost of equipping workers with portable air quality monitors has been calculated at about $1.00 per day per worker.

What the study discovered is that fatality figures being used by some professionals in verbally reported incidents were vastly overstated, which did not earn the study’s authors any popularity contests in some quarters, particularly with some organizations that were receiving significant funding to operate certain farm safety programs. However, the study has painted a more realistic picture of what has occurred in terms of documented manure gas related injuries and fatalities. While these cases have been documented, the authors have no doubt that there have also been many undocumented near-misses or mis-reported fatalities related to manure gas exposure.

Farm workers and manure handlers need to be alert to telltale signs of a potentially hazardous environment. Firstly, animal behavior is a good indicator. If animals are quiet and sluggish, this can indicate the presence of toxic manure gases and the facility should be ventilated immediately. Secondly, if workers experience dizziness and disorientation, they should seek fresh air immediately. In cases where an individual is disoriented and remains in that state after exposure to manure gases, medical attention should be called upon immediately because more serious side effects could follow, such as permanent brain injury.

In addition to pinpointing the actual number of deaths that can be blamed on manure gas asphyxiation, the study provides some noteworthy data for manure haul contractors and farmers on where these deaths occurred. Below-ground manure storage structures and sump pits accounted for 65 or 84 percent of the 77 fatalities while open lagoons only accounted for eight of the documented cases. A total of 22 percent of total fatalities occurred during a rescue attempt. At the time of death, most of the victims were unclogging, cleaning, repairing, moving, retrieving, fixing and checking equipment and facility components.

Of particular concern is that 17 of the victims were under the age of 16, an age group that – according to the Fair Labor Standards Act and Hazardous Occupations for Agriculture – is prohibited from working for hire in agricultural confined spaces.

The cost of equipping workers with portable air quality monitors,
similar to this model marketed through Dräger Safety, has been
calculated at about $1.00 per day per worker.
Photo Courtesy Of Dräger Safety.

Time of year also factored into the highest occurrence of fatalities as, according to the authors, “the peak period of incidents were during the hottest part of the summer and often associated with transferring of manure for application to crop ground.”

Part of the problem with challenging the farm community to identify and take preventative action to avoid contact with toxic manure gases, says Field, is that so much of the research as it relates to the potential dangers of manure gases is focused on maximizing animal health rather than on protecting farm workers. That is because the industry is so focused on production. There is a trend toward leniency as it relates to applying the same standards to farm operations as compared to industrial facilities. For example, safety regulations related to confined spaces for industry do not apply to farm facilities. Field is concerned that it may take a major farm tragedy before legislators hear a wake-up call as to the importance of applying these safety measures equally for farm-based confined spaces such as manure storage pits.

He also points out that there are standards specifying how municipal waste facilities must be designed so that workers can properly maintain the facilities without putting themselves in mortal danger from sewage gas. Yet no such standards exist for the construction of manure storage and handling facilities on farms. He notes that when conducting research for the study, researchers witnessed many examples of older farm manure storage and handling facilities where piping was located in dangerous cramped quarters and constructed with steel components in regular contact with manure that were in advanced stages of corrosion.

Nor is there any data as to the dangers of long-term exposure to toxic manure gases. Only now is money being spent to establish a baseline to determine the quantity of manure gases within typical farm operations. All that is known, so far, is sows that live in an environment of prolonged exposure to manure gases tend to experience more aborted births. Therefore, Field says common sense would suggest that women in their child bearing years may want to avoid exposure to confined livestock areas where manure gases could be a concern.

The study makes several recommendations as to how fatalities may be avoided in the future. What is noteworthy is the number of deaths per year is increasing, largely due to changing manure storage practices over the past 30 years. Many suggestions relate to how incidents can be prevented in the first place through engineering controls in manure handling and storage facility designs as well as through worker safety education.

The authors suggest that manure and waste pits should be identified as confined spaces; manure and waste systems should be constructed in a manner that would allow maintenance to be performed on all serviceable components from outside the pits; manure waste systems should be equipped with some type of power ventilation system; manure storage or pits should never be entered unless absolutely necessary; entrances to waste pits should be covered by a grate-like cover; farm employees must be instructed never to enter a manure pit, or any other confined space to attempt a rescue operation, without proper consideration of their own safety and the appropriate equipment to conduct the rescue; and, manufacturers of equipment designed for manure waste pit systems should include warnings on the hazards associated with these systems.

Animal behavior is a good indicator of the possibility of manure gas
build up. If animals are quiet and sluggish, this can indicate the
presence of toxic manure gases and the facility should be ventilated

Other suggestions include limiting or restricting access through fencing, placing sufficient ‘danger’ or ‘warning’ signage in the vicinity of confined spaces, using air monitoring equipment and maintaining adequate ventilation. -end-

Manure storage safety procedures

Avoid entering manure storage areas if at all possible. Many deaths have occurred when people entered manure storage areas without proper safety precautions. If you must enter a manure storage area, the following confined space entry procedures will minimize, but not eliminate the risks.

  • Never enter a manure pit during or just after agitation because there is always the possibility of deadly concentration of this gas. Plumbing and pumping equipment should be installed so that it can be easily removed for repairs. Before agitation, take steps to ensure the welfare of the animals and people working in the area.
  • Remove all people and animals if possible. If animals cannot be removed, maximize ventilation and agitate slurry very slowly at first. Monitor the condition of the animals. If the animals act restless, agitated or abnormal, stop the agitation immediately and ventilate the area.
  • Always keep at least one foot of space between the highest manure level and the slats. This protects animals which are on the slats and inhale the gases that accumulate at the surface of the pit.
  • Do not enter manure pits without either a self-contained air supply like those that fire fighters use, dust masks or other cartridge respirators will not filter out the toxic gases nor will they provide the oxygen requirement to work in confined spaces such as manure pits, or test before entering. Test the oxygen level to make sure that adequate oxygen is available. Also test for hydrogen sulfide, a particularly toxic gas, to be sure that concentrations are safe – less than 10ppm.
  • Provide additional forced ventilation. Additional ventilation will increase oxygen and decrease hydrogen sulfide and other toxic gases.
  • Monitor conditions while working. Agitation from working can increase the toxic gas levels. When someone collapses in a pit, gases are so concentrated that it is suicidal for anyone else to enter without a self-contained breathing apparatus. The only reasonable immediate action is to ventilate the storage area and notify rescue personnel who can bring the proper equipment.
  • Barn fans may be activated to provide ventilation, but do not lower fans into the pit because this could cause a methane explosion.
  • Use a safety line. A worker in a confined space or manure storage area should wear a body harness with a safety line. Enough people and/or a winch should hold the safety line so that the worker can be pulled out of the area if a problem develops.
  • Wear a supplied air respirator. Never enter a pit without one. The person using a respirator should be trained on the use of the mask. It is particularly important that the mask form a tight seal around the face.
  • Provide a clear escape path. Make it as easy as possible for the worker to exit the manure storage area quickly. Do not block the path with tools or objects.
  • Keep fire away. Methane gas is a by-product of manure degradation and it is flammable. Keep fire and other ignition sources such as electrical tools away from the manure storage area. Test the methane level with an explosion meter.
  • Know first aid. Someone on the site should be trained in CPR and first aid.
  • Recognize that conditions are of greatest risk when manure is agitated or moved. Movement and agitation increase the release of dangerous gases, sometimes several fold. When agitating, pumping, or moving manure, take precautions to be sure that extra ventilation is provided to nearby areas (e.g., buildings over or near the manure storage).

Due to the equipment requirements and inherent risks associated with entering an area where there may be toxic gases or insufficient oxygen, you should consider hiring a professional trained in working in these areas to perform maintenance tasks. If hiring a professional or using a SCBA is not possible, the best advice is to stay out of the pit. -end-

Information courtesy of Farm Safety Association Incorporated.


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