FIRES IN AGRICULTURAL SILOS

FIRES IN AGRICULTURAL SILOS

VOLUNTEERS CORNER

The deaths of two firefighters on August 5, 1993, in Morgan County, Georgia, during the suppression of an agricultural silo fire is a grim reminder of the need for education in farm emergencies. The two died as a result of an explosion of an oxygen-limiting silo into which they were directing a hose stream. This tragedy, unfortunately, has occurred across the country numerous times. This article examines the generally accepted approach to preplanning, assessing, and extinguishing a fire in an agrictiltural silo.

An estimated one million vertical silos are present in North America. They occasionally are the sites of fires in rural settings, where they are used to store chopped forage, usually hay or corn, for subsequent feeding to livestock. Silos stand up to 130 feet tall and are constructed of steel, concrete, tile, or wood.

Silo fires usually occur when farmers fail to follow proper forage storage procedures. These fires produce gases that include carbon monoxide, carbon dioxide, and oxides of nitrogen. Therefore, positive-pressure SCBAs, full protective gear, and confined-space techniques must be used when dealing with silo fires. Explosions in agricultural silos should not be considered to be the same as explosions in grain elevators. Grain elevator explosions are a result of very dense dust environments that detonate from a spark within the elevator.

PREPLANNING

Successful suppression of fires in silos begins with education and preplanning. Firefighters must be familiar with the structure, its function, and its hazards. Preplans on silos in your district should include the following:

• type and brand of silo and silo unloader,
• owner and manufacturers’ representatives,
• normal type(s) of contents,
• location of electrical power disconnects,
• exposures and their contents,
• water sources,
• silo dimensions and age, and
• modifications.

Having this information and keeping it current will save time and perhaps firefighters’ lives.

SILO FIRE SUPPRESSION

The method of controlling fires in silos depends on the kind of silo involved. Always be sure to determine if the silo has been modified. Two firefighters were severely injured in a silo explosion in New York State in 1987 when they directed water into an oxygen-limiting silo that had been modified into a more conventional style by the farmer. The farmer had cut unloading doors along the length of the silo and had plans to assemble a conventional-type unloader above the silage.

Conventional silos. Conventional silos typically are constructed from poured concrete, concrete staves (curved concrete blocks held in place by steel rings), steel, tile blocks, or wood. Silos usually can be identified by the approximately three-foot-diameter chute that runs the length of the silo. The chute allows the silage to fall down into the bam or wagon during the unloading operation. The silos may have no roof or a tall domed roof.

Fires in conventional silos pose little threat of explosion because the silos are not designed to be sealed structures. Time is also in the firefighters’ favor unless exposure problems develop. On arrival at a conventional silo fire, you should do the following:

• confirm your preplan information on the silo involved;
• have the owner/operator and silo dealer respond:
• check for and extinguish any hot embers that may have left the silo;
• have the farmer move any livestock, machinery, etc. from the area and adjacent structures, if possible;
• by means of a hand crank or electrical switch at the base of the silo, raise the silo unloader machine as far up as possible to minimize damage to its parts, and
• disconnect the electrical supply to the silo unloader.

At this point, a firefighter with full protective gear, including SCBA, and a lifeline must assess the fire from above the silage. This can be done by utilizing an aerial ladder or climbing the exterior or the chute of the silo. Use extreme care when climbing silos. The ladders and steel rungs usually are very slippery. In addition, the chute ladder may have been damaged by the fire. The chute also may be full of hot embers. Once above the fire, the firefighter should extinguish any visible hot spots.

The fire typically can be located around the perimeter, the unloading doors, and the top few feet of silage. A fire burning for an extended period of time can create hollowed-out areas in the silage. Therefore, any firefighter entering a burning conventional silo after knockdown of the burning surface must be secured with lifelines and stand on long boards or ladders. There are no interior ladders, per se, only the steel support rings at the chute opening. At this point, penetrating nozzles can help to reach subsurface burning. Confined-space techniques must be followed in silos.

It usually is impossible to completely extinguish fires in conventional silos. Even when the fire appears to have been extinguished, it sometimes reignites. The farmer must partially or sometimes totally empty the silo. You may have to be present during this unloading to douse hot spots. When unloading is an extended operation, consider rotating personnel.

(Photos by authors.)

Using carbon dioxide or nitrogen to extinguish conventional silo fires is a questionable practice, since the structure is open to the atmosphere and oxygen usually can still reach the fire. Some departments have had some success with these gases, but more experimentation must be done.

Oxygen-limiting silos. Unlike conventional silo fires, fires in oxygen-limiting silos can cause an explosion, as was the case with the two Georgia firefighters mentioned above and in an incident during which three Ohio firefighters died in 1985. The firefighters were killed when they injected water and/or foam into a burning oxygen-limiting silo. Since these structures are designed to limit the amount of oxygen inside, allowing any air to enter the silo can cause an explosion. Therefore, do nothing that may cause air to he drawn into the silo. Do not attempt to open hatches or spray water or foam inside.

You can recognize oxygen-limiting silos by the absence of an exterior chute. Also, their roofs are slightly less sloped than those of conventional silos. There are various brands of oxygen-limiting silos. Some are constructed of steel and others of concrete. It is imperative that firefighters know when this type of silo is involved in an incident. You must identify oxygen-limiting silos in your preplans.

Response to a fire in an oxygen-limiting silo should involve the following steps:

• Confirm your preplan information.
• If the structure is shaking, hot, noisy, or smoking heavily, stay off it. If you are unsure, stay away from the structure.
• Have the farmer and silo dealer respond.
• Do nothing that will increase the amount of oxygen inside the silo. Do not -. open hatches or unloader doors, and do not inject water or foam.
• Inspect for extension into any adjacent structures and have the farmer evacuate these structures if possible.
• If the structure is quiet, motionless, and cool and if smoke is minimal, close the “ bottom unloading door and top hatches, if open. Do not lock down these hatches. This will allow the silo to vent itself. ~
• Leave the silo closed for two or three weeks. If the structure is well sealed, the fire may self-extinguish.
• If the fire continues to bum, you may have to inject carbon dioxide or nitrogen. Ask the silo dealer for assistance.

Usually there is no great hurry to extinguish silo fires. They generally are well contained by the structure. Rushing into fire suppression activities can be disastrous. Silo fires are not common, but the possibility of firefighter death and injury is always present. Rural fire departments could benefit greatly by preplanning the farms in their districts and by taking farm rescue and firefighting training courses.