CSB issues update on Horizon Biofuels explosion investigation

The U.S. Chemical Safety and Hazard Investigation Board (CSB) yesterday provided an update on its ongoing investigation into the fatal July 29, 2025 explosion and fire at the Horizon Biofuels facility in Fremont, Nebraska.

The incident resulted in the deaths of three people - an operator and his two young daughters, ages 8 and 12.

“This terrible tragedy should not have happened,” said Steve Owens, CSB chairperson. “Preliminary evidence points to a combustible wood dust explosion, a well-known - and completely avoidable - hazard in wood processing.”

At the time of this update, the CSB said the Horizon Biofuels facility remains unsafe and officials have advised that people maintain a safe distance from the facility due to the potential for the structurally-compromised building to collapse, also preventing the CSB from approaching the building so far.

The CSB said its investigation plans to examine the operations and conditions at the Horizon Biofuels facility, as well as dust control systems, industry guidance for safe dust operation, and regulatory oversight.

A combustible dust explosion can occur when certain conditions align at a facility, including dust accumulation, dispersion, and ignition within a confined space, potentially triggering a powerful secondary explosion, like the one that occurred at the Horizon Biofuels facility.

Fires continue to smolder in Fremont

The incident occurred at the Horizon Biofuels facility shortly before noon on July 29, following a sudden release of dust or smoke from an elevator tower, quickly followed by flames and a much-larger, major blast that caused significant structural damage.

The day shift operator, who had brought his two young daughters to work with him, was trapped inside the collapsed structure and died. His two daughters, who were in the break room at the facility, also were killed in the explosion.

Emergency responders were unable to enter the unstable, burning building until the following day, when they recovered the bodies of the three fatally injured people. The explosion caused severe damage within the facility, affected vehicles on-site and nearby, and led to road closures that disrupted local businesses for several days.

Several fires also occurred at the facility, and combustible material has continued to smolder there for more than a month.

CSB to evaluate dust control systems, procedures

The CSB previously has investigated a number of combustible dust incidents across industries.  Additionally, in 2006 the CSB issued a major study of combustible dust incidents involving 281 dust explosions that resulted in 119 deaths and 718 injuries.

“The Board is committed to a thorough, independent investigation, said Sylvia Johnson, CSB board member. “We owe it to the victims, their families, and the broader community to identify the root causes and share important safety lessons.”

The CSB said its ongoing investigative actions of the Horizon Biofuels incident include:

• Examining the facility’s design, process flow, dust handling, and dust control systems, including cyclones and dust collectors.
• Assessing whether the facility site operating procedures and practices met safety standards.
• Interviewing employees, management, first responders, and others knowledgeable about the facility’s operations, maintenance, and safety practices.
• Reviewing the conditions at the facility and whether prior audits or inspections addressed combustible dust hazards in the facility.

The CSB continues to gather facts and analyze several key areas, including:

• Cause or probable cause of the initiating dispersion of dust
• Events and conditions at the facility prior to the incident
• Post-incident equipment condition and failure analysis
• Properties of combustible wood dust
• Industry guidance for facilities that generate wood dust
• Regulatory analysis