A Summary of Fatalities and Injuries Involving Horizontal Bunk or Open Pile Silos Used in Agricultural Production

The frequency of horizontal silo-related fatalities and injuries was lower than anticipated, based upon historical media coverage. Horizontal bunk silos are a safer design than conventional tower silos based upon the frequency of documented cases. Implementing prevention strategies should focus on dairy and beef production operations. Consideration should be given to incorporating recommendations on safe work practices in the current ASABE bunk silo design standard. Workers should be trained to keep no less than the height of the silage pile away from the face of the silage when entering the silo for any reason, including when sampling silage. The frequency of both fatal and non-fatal bunk silo incidents does not justify significant changes to federal workplace safety regulations.

Horizontal bunk silos, including open or surface storage of silage, though not new concepts, have rapidly replaced conventional wood, concrete stave, and steel tower silos at dairy and beef production operations. Horizontal silo designs have allowed for much larger capacities, in some cases exceeding thousands of tons. These storage structures have reduced the need to climb 70-120 feet (21.3-37.6 meters) vertically to access the surface of the silage or internal equipment, such as distributors and top unloading silo unloaders for service or repair. The use of horizontal silos has increased the filling and unloading rates by eliminating the restriction of forage blower capacities and height limitations. Furthermore, they have contributed to increased uniformity and quality of silage due to more rapid filling and increased packing density. However, a relatively few highly publicized injuries and fatalities over the last decade involving these structures have resulted in considerable attention by agricultural safety and health professionals and enhanced regulatory enforcement by state and federal Occupational Safety and Health Administrations (OSHA), resulting in citations for unsafe work practices and civil litigation due to personal injuries and economic loss. There has been, however, no reliable assessment of the frequency and severity of these incidents upon which to develop effective evidence-based prevention strategies or assess relative risk between silage handling practices. Research was undertaken to identify and document horizontal silo-related injuries and fatalities building on cases included in the Purdue Agricultural Confined Space Incident Database (PACSID), OSHA reports, the National Institute for Occupational Safety and Health's Fatality Assessment and Control Evaluation (NIOSH FACE) reports, online databases such as AgInjuryNews, state farm fatality summaries, and prior legal litigation. Approximately 2,400 cases identified as occurring in agricultural confined spaces, including "silos," and related structures were reviewed. A total of 33 cases, involving 35 individuals, were confirmed as having occurred in the U.S. in bunk-type silos or associated with open silage storage piles between 1962 and 2023. This frequency was considerably lower than originally anticipated. In some instances, the same cases were repeated by the media numerous times, giving the appearance of multiple incidents. Of the cases examined, the primary contributing factors were suffocation due to being buried by collapsed silage caused by undercutting of the silage face or silage instability, being crushed by a tractor rollover, entanglement during silage packing operations, and falls from the silage surface or sidewalls. In addition to farm operators and farm workers, victims included veterinarians buried at the face of the silage while attempting to collect silage samples for nutritional analysis. Prevention recommendations include discouraging the overfilling of bunk silos, restricting unprotected worker access to the face of the silage at any time, especially if overhanging silage is present, use of appropriate unloading equipment that can access the full face of the silage and still protect the operator, safer means of accessing the top surface of the silage, and restriction of packing equipment to only vehicles equipped with rollover protection for the operator. Prevention strategies should target primarily dairy and beef producers with horizontal or open pile storage of silage. The inclusion of warning signage and safer access to the surface of the silage pile for removal of coverings should be considered. Considering the infrequency of these incidents, the need for additional regulatory language does not appear justified. The need for an expanded engineering standard for bunk silos that includes a safety component, such as safety signage, should, however, be considered.