Should hydrogen-sulfide monitors be worn on swine production sites during manure transfer?
Hydrogen sulfide (H2S) is a toxic, colourless, flammable gas — a byproduct of anaerobic bacterial reduction of sulfates. Anytime manure is being agitated, or when shallow-pit plugs are pulled, there is a potential for airborne concentrations of H2S to become elevated, potentially putting both workers and pigs at risk of being overexposed.
The H2S concentration considered immediately dangerous to life and health is 100 parts per million (ppm). Above 600 ppm, a person can die after only one or two breaths. It is important for farms to identify situations and practices in which there may be increased amounts of airborne H2S. Field studies have shown that H2S concentrations can exceed this level quickly during slurry agitation with concentrations recorded as high as 1,300 ppm.
Human detection and awareness
Human exposure to hydrogen sulfide is primarily through inhalation. The “rotten egg” smell can be detected at low levels, but with continuous low-level exposure or at higher concentrations, the ability to smell the gas — even though it is still present — is lost. The ability to smell H2S may begin to dull at 50 ppm. You cannot depend on your sense of smell for indicating the continuing presence of H2S or for warning of hazardous concentrations.
H2S awareness training on swine farms in Canada has proven effective in changing attitudes regarding safety of employers and employees. Hydrogen-sulfide monitors are being used when liquid manure is being agitated or when pit plugs are pulled within barns systems.
Training for H2S covers properties of H2S, exposure limits, detection and the importance of standard operating procedures and emergency-response plans. Pork producers should be quick to appreciate the importance of H2S monitors. First, they provide early detection of the gas within a facility. This knowledge, when coupled with employee training, helps people understand when to exit that facility immediately.
The monitor can also be used to determine if, after turning on the ventilation, the H2S level is lowered and it is safe to enter. Individual monitors can be purchased for a reasonable cost of $130 or up to $1,000, depending on battery life and sensory levels.
Similar to stories of coal miners, the pig might be the unsuspecting canary. It is not unusual for producers and veterinarians to find one or a few dead pigs housed in pens that have “dead air” or limited air exchange during or immediately after manure transfer.
“We lost 200 head of finishing pigs to hydrogen-sulfide poisoning during routine manure pumping,” explained one farmer. “We were walking back from lunch with assignment to scrape pens, and fortunately, our father recognized the ominous silence as we neared the finishing barn. Had he not been with us, three of his children would have walked into the same fate as those pigs.”
It is known that H2S is sometimes released during manure agitation. While the number of cases submitted to Iowa State University Veterinary Diagnostic Laboratory (ISUVDL) due to H2S toxicity is relatively few, the true incidence of H2S intoxication is likely to be underreported. Field observations by Drs. Steve Ensley, Wilson Rumbeiha and Kent Schwartz at ISUVDL suggest that livestock death typically occurs on the same day as manure agitation in barns with deep pits.
Warning signs are inconsistently present, but may include mucosal, corneal, conjunctival and/or respiratory tract irritation. ISUVDL is currently working on diagnostic biomarkers in serum and urine of affected pigs.
Rescue and recovery
If overcome by H2S, it is important to note that a rescuer has only about six minutes to apply cardiopulmonary resuscitation. The victim or the rescuer will require a self-contained breathing apparatus — like the ones firefighters wear — to enter the space and, most likely, recover the exposed individual. The majority of hydrogen-sulfide poisonings (approximately 86 per cent) occur in confined spaces, and many poisonings are the direct result of others trying to help co-workers in need. Use of H2S monitors and training help avoid these tragic outcomes.
Recommendations for farmers during manure transfer:
Madonna Benjamin, Beth Ferry, Jerry May, Tom Guthrie, Shelby Burlew, Dr. Ron Bates and Dale Rozeboom are researchers with Michigan State University in East Lansing.