If you can't see the manure, then you can't smell it. Right?

Not necessarily, but public perception is a major driving force behind the industry trend of building deep-pit manure storage units.

Some of you may have determined that with strict environmental regulations a deep pit is your best bet. In some states, it's nearly the only way to get a hog building permit.

That's what producer Dale Holmgren found. He and his brother, Tom, are expanding their farrow-to-finish operation outside of Mankato, Minn. The plan is to grow from 380 sows to 700 sows.

Holmgren admits that construction permits for deep-pit buildings are much easier to receive in Minnesota and there is less resistance from neighbors.

The pits also can temper odors, he contends. In the Midwest, an outside lagoon or slurry storage unit will freeze in the winter and will usually turn over in the spring and fall, sometimes producing strong odors.

Another advantage of deep pits, Holmgren notes, is that the manure maintains a high nutrient value as fertilizer. It can almost double that of a lagoon. When you pump the lagoon, some of the valuable nutrients, especially phosphorus, may be left behind.

Although deep pits have advantages, there are still questions surrounding this manure storage system. Most notably is that of the building's air quality.

"I'm concerned that we're transferring the problem from outdoor concerns to indoor air quality ones," says Larry Jacobson, University of Minnesota agricultural engineer.

The buzz in the industry now focuses on outdoor odors, but Jacobson says this could change. When we talk about such things as worker satisfaction – including a pleasant working environment – indoor air quality becomes an issue.

"In the future, this will be more important than some of the perceived odor issues," Jacobson says.

So far, Holmgren hasn't had any air quality problems in his buildings. His finishing building has two pit fans in each room, and the gestation barn has four per room. Even if one fan quits working, there's a backup.

In deep-pit buildings, the biggest hazard occurs when the pits are being agitated. Jay Harmon, Iowa State University agricultural engineer, cautions that when hydrogen sulfide levels exceed 50 parts per million, it paralyzes your olfactory senses. That means you can't smell, and you lose the ability to judge if there's a problem. Hydrogen sulfide at that level is highly dangerous.

"You should never remain in a building when the pit is being agitated," Harmon stresses.

It's also best to agitate the pits when there are no hogs in the buildings. Deep pits are usually pumped once a year – in the spring or fall. So finding a time when the building is empty, the pit is full, and weather and field conditions are ideal doesn't often happen.

The key to managing deep-pit buildings is pit ventilation. But how do you know if you have enough? Steve Hoff, Iowa State University agricultural engineer, is trying to find out. Hoff is looking at performance testing for mechanically ventilated livestock systems.

"Pit ventilation systems exist to help prevent pit gases from entering the pigs' breathing zone," Hoff explains. "However, these systems affect only a small portion of the head-space region and do not represent the final story." The head space is the area between the top of the manure and the underside of the slats.

His research shows that it's common practice for producers to draw minimum ventilation air through the pit. The perception is that these pit fans pull in air and prevent pit gases from entering the breathing zone.

"That's clearly not what happens," Hoff says. "I've found that the proper airflow required to guarantee that pit gases won't enter the breathing zone is much higher than minimum-ventilation fans can provide."
With minimum-ventilation fans, he notes, you pull a small portion of air through the slatted floor to the fan, but a large portion of the pit remains poorly ventilated.

At minimum-ventilation rates, you would have to reduce the floor opening to get proper air movement through the slats. Ideally only 5 percent to 6 percent of a slatted floor's area would be open for air movement and drainage. However, at that rate it would be difficult to get manure through the floor opening because there wouldn't be enough openings.

Hoff explains that you typically need a 14 percent to 17 percent floor opening to keep pens clean. This is the percent opening currently used for full-slatted barns. He is trying to come up with a better method to ventilate the pit area and still maintain a high-percentage floor opening.

So what's the answer? There isn't one yet. "We obviously need to maintain certain minimum floor openings to guarantee that manure gets into the pit, and we can't get it with a 5 percent to 6 percent slat opening," Hoff explains.

He and other Iowa State engineers are working on a solution. It consists of a new inlet system that attempts to provide fresh-air ventilation in the head-space region to dilute the gases in case they enter the pigs' breathing space. But this system is still being developed.

In other studies, Hoff found that air inlets placed too near the walls will channel air down the wall and into the pit, displacing pit gases into the room. You can avoid this problem by placing air inlets at least 15 feet in from the walls.

Although Hoff says he realizes there are potential drawbacks to deep pits, he's not opposed to them if proper precautions are used. On the other hand, John Hoehne, University of Missouri agricultural engineer, isn't an advocate.

Like other engineers, Hoehne is concerned about the indoor air quality. If you have the land available to build an outdoor concrete tank, he still prefers this option. He also prefers a shallow, pull-plug manure removal system inside the building.

Another potential drawback of a deep-pit system is the extra installation cost. Depending on where you live and the construction requirements, you could have more money tied up in a deep pit compared to the cost of a lagoon.

However, if you live in Minnesota or another state with extremely cold winters and tough environmental opposition, the extra cost may be worth it. "We have to put in such deep footings (usually four feet) under a barn, so the cost is comparable to lagoons in Minnesota," Holmgren explains.

For now, the outdoor environmental advantages of deep pits are outweighing the indoor disadvantages – at least in some states. So if deep pits are the route you choose, make sure to install enough ventilation to keep your pigs and your workers safe.

Are Deep Pits Hazardous to Your Health?

Indoor air quality in hog facilities is rapidly becoming a big issue with the resurgence of deep-pit buildings.

Iowa State University agricultural engineers Jay Harmon and Hongwei Xin developed this outline of potential health hazards to be aware of, monitor and address in hog confinement buildings.

AMMONIA
Odor: Sharp, pungent.
Target level for swine: Less than 10 parts per million.
Sources: Urine (urea) drying on solid floors, slats and in scraper gutters.
Possible solutions: Prevent manure from drying by keeping manure in solution through pit recharge. Increase pit ventilation, especially with a deep-pit manure system.
Human effects: 10 to 15 ppm irritates nose and eyes. May irritate bronchi and cause bronchitis. May irritate bronchioles (asthma). May cause long-term deep lung effects.

HYDROGEN SULFIDE
Odor: Rotten-egg smell, nauseating.
Target level for swine: Less than 5 ppm.
Sources: It's produced during anaerobic degeneration of manure, especially in deep pits. It can be deadly when manure is being agitated in a storage pit.
Possible solutions: Dilute manure. Ventilate pit properly. Agitate manure in pit with all fans running. Never enter a building while agitating the pit. Store manure outside if possible.
Human effects: 1 to 5 ppm, you will detect a rotten-egg smell. At 50 to 100 ppm, you will have olfactory paralysis, meaning you can't smell it. Greater than 100 ppm, rhinitis (runny eyes); 100 to 150 ppm, bronchitis (dry cough); 200 to 500 ppm, headaches, dizziness, nausea, pneumonius and pulmonary edema (symptoms like pneumonia, like tuberculosis in hogs). Greater than 1,000 ppm, rapid respiratory arrest, death (requires only one to three breaths at this level.)

CARBON DIOXIDE
Odor: None.
Target level for swine: Less than 3,000 ppm.
Sources: Exhalation, unvented heaters and anaerobic manure decomposition.
Possible solutions: Increase ventilation rate.
Human effects: 30,000 ppm, increased breathing rate, headaches and drowsiness; 300,000 ppm possibly fatal.

DUST
Odor: None.
Target level for swine: Less than 10 milligrams per cubic meter.
Sources: Dried fecal matter, feed, animal hair, animal skin and bacteria. Deep pits alone don't contribute to dust problems unless slat surface area is such that it promotes manure and feed collection.
Possible solutions: Keep building clean to prevent manure from drying onto surfaces. Use feed drops and feeder lids. Use pelleted feed or add fat to feed.
Human effects: Respiratory irritation, especially with particles less than 5 microns in size. Respirable dust operates as a conveyance mechanism for disease pathogens.