This afternoon I received a telephone call about another barn explosion associated with a foaming pit. While there have been several of these in the past few years, what is unique about this site is the pit blew up again 2 days later while workers were in the barn making repairs.
I was surprised when I got the call as one would expect pit temperatures to have declined by now resulting in less bacterial activity. Also, pit levels are generally low this time of year.
Here are the details. The facility is a wean-finish barn in the Midwest. The pit had a couple of feet of manure and was noted to have a couple of feet of foam. It had been empty for 10 days or so. The first explosion occurred within a couple of hours of when the first weaned pigs were placed in the barn. The pig owners think the ignition source was a propane brooder. Several pigs were killed and the plastic feed lines melted, etc.
Two days later repair crews were at the site. The side wall curtains were down and the pit fans operating when a second explosion occurred. This explosion resulted in first and second degree burns to some of the repair crew personnel. The explosion was in the same general area of the barn as the first explosion and most likely was ignited by a furnace pilot light.
As I talked thru the event with the field supervisor for the production company, we concluded that lowering the curtains when the repair people were in the barn was the wrong thing to do. While there was some wind on the day of the repairs, I speculated that the explosion most likely occurred in a location within the barn that was relatively ‘dead’ in terms of air exchange due to the orientation of the barn to the wind that day.
A better strategy would have been to leave the curtains up and turn on ventilation fans. When the room is operated in this manner, static pressure from the fans means air must enter the room from the ceiling inlets. If the ventilation system is designed correctly and functioning correctly, there should be little change of dead air pockets and pockets of high methane concentrations from the decaying foam in the pit. The ceiling inlets are designed and installed to provide air to all parts of a facility, something that open curtains aren’t very good at in some circumstances.
What does all of this mean? It means foaming is now more than just a late summer and fall problem. The risk of explosion when the foam is disturbed or broken is very real. This is the first report I’ve had of foaming in late winter which suggests pits are more biologically active than we previously thought. It also means that unless the ventilation system is functioning correctly and turned on, there is a very real risk of a second explosion when workers are present in the facility repairing the damage from the first explosion.
So far, this is a growing industry concern that has eluded easy solutions. If you have a foaming pit, be very aware of potential ignition sources and keep the fans running!