Automated manure and wastewater handling for livestock and dairy production is most often accomplished by collecting and storing manure and waste in storages located directly beneath the animals or in a nearby containment structure that may be located either belowground or at ground level. The collection system often involves a smaller belowground pit for pumping manure to a longer-term storage structure or directly into a manure spreader. While this method is efficient, it can create a unique set of hazards.
Manure storages and confined spaces
Most belowground manure storages, aboveground tanks and transfer structures meet the definition of a confined space: large enough and so configured that a worker can enter and perform work; limited or restricted means for entry or exit; and not designed for continuous human occupancy. Hazards include lack of oxygen, toxic and flammable gases, and exposure to drowning.
Once a person has entered a confined manure storage area, it is often too late to mitigate the associated hazards. Gases generated by manure are colorless, sometimes odorless, and easily masked by other common farm smells. For example, hydrogen sulfide, one of the most dangerous manure gases, has an odor but it is often undetectable above 100 parts per million because it deadens the sense of smell.
Fatalities occur when workers enter facilities and are overcome by toxic manure gases or exposed to an oxygen-deficient atmosphere.
Monitoring gas levels
Use of a hand-held gas detection monitor prior to and during any entry event is highly recommended. These monitors must be properly calibrated, maintained and used.
Portable monitors can provide a reliable digital readout of the gas levels present, as well as warning alarms. Many newer portable detectors can measure multiple gases, including oxygen.
Recalibrate these detectors periodically according to the owner’s manual. Battery-powered units should be checked regularly to ensure they are fully charged.
Monitoring can also be done with gas detector tubes, which contain a reactant that changes color based on the gases that are present and their concentration. The drawbacks are the delayed time in which gas levels are displayed and the lack of an accurate measurement (it can differ by as much as 25 percent from the actual gas level). Manure gases, especially hydrogen sulfide, are particularly critical at higher levels, and any delay in detecting or accurately measuring these dangerous levels is life-threatening.
Mechanical ventilation systems
A specially designed, positive-pressure, mechanical forced-air ventilation system is needed to reduce risks. It forces air into the storage to replenish oxygen levels and mitigate a buildup of dangerous levels of manure gas. Forcing fresh air through a fan into the storage reduces the risk of fire or damage from exposing electric fan motors to manure gases. The ventilation fan should be capable of moving a volume of air equal to at least 0.5 times the volume of the empty manure facility every minute. The fan can be permanently installed or portable.
New manure storages should be designed with permanently installed positive-pressure ventilation systems. All ventilation systems should be connected to a standby power system.
Never enter a manure storage when the manure is being agitated or while emptying it.
Ventilation efficiency is improved and ventilation time prior to entry is reduced when intake air is ducted from a fresh air source that is not contaminated by manure gases exhausted from the storage. Ventilation system ducting should be cleaned as needed to remove dust and other material. The fan guard should be removed periodically to clean the fan housing and blades.
All confined-space manure storages located away from but interconnected to animal living quarters should use gas traps in transfer pipes to prevent gases from flowing back into the animal housing area.
Entering a confined-space manure storage will always entail some risk and should be avoided if possible. If you must enter, there are several actions you can take to reduce risk. These actions are applicable for entering storages that are currently being used or that may have been empty and unused for months or years:
* Test from outside for contaminant gas and oxygen levels before entry. The person entering should be able to observe all pre-entry testing.
* Ventilate the manure storage with a positive ventilation system prior to and during the entry event.
* The person entering should wear an adjustable body harness with a lifeline attached to a combined rescue and retrieval system. This person should also have a portable gas and oxygen monitor to protect against rapidly changing conditions.
* A second person should be available and stationed at the entrance. This person should be able to use the rescue and retrieval system to lift the person out of the storage in case of emergency.
* This second person should maintain either visual or verbal contact with the person in the storage. This person must also be mentally and emotionally strong enough not to enter the storage in case of emergency.
Additional suggestions to reduce risk include posting danger signs at all entrances to the storage; informing family members, employees, contractors and visitors about the dangers of confined-space manure storages; and preparing a written confined space entry procedure.
Adapted from the Penn State Extension publication “Confined Space Manure Storage Hazards” by Joel S. Steel, senior research associate; Dennis J. Murphy, professor; and Harvey B. Manbeck, professor emeritus.