The 1969 Rocky Flats Fire: The Accident That Brought Rocky Flats Into Public View

On Mother’s Day 1969, plutonium caught fire inside one of Rocky Flats’ major production buildings. Firefighters battled the blaze for hours, portions of the filtration system were damaged, and plutonium was released. The accident would become a turning point in how Colorado understood the nuclear weapons plant operating outside Denver.

On Sunday, May 11, 1969, another major plutonium fire broke out at the Rocky Flats Plant.

It had been less than twelve years since the devastating 1957 fire. This time, the fire occurred in the North Foundry glovebox line in Buildings 776/777, a major plutonium-processing facility.

According to Colorado's later Historical Public Exposures Study, the fire began at about 2:00 p.m., when a pressed plutonium-metal briquette stored in an open can spontaneously ignited. At 2:27 p.m., an alarm reached the plant fire station. Two minutes later, firefighters arriving at the building encountered flames extending roughly 18 inches above the glovebox line.

What followed became one of the most serious accidents in Rocky Flats history.

A plutonium fire inside the glovebox system

Plutonium work at Rocky Flats was conducted inside enclosed gloveboxes intended to contain radioactive material while workers manipulated it from outside. During the 1969 accident, the fire spread along the North Foundry glovebox line and then into another connected glovebox line. Firefighters heard loud noises and observed fireballs. Smoke eventually appeared from the building's roof and exhaust vents. The fire was considered contained by approximately 6:40 p.m. and extinguished by about 8:00 p.m., although smaller fires recurred during the night and into the following morning. Firefighters faced an especially difficult decision. Because water around significant quantities of plutonium could create concerns about nuclear criticality, its use had been restricted except as a last resort. The building therefore did not have the automatic sprinkler protection we might expect in a facility containing combustible materials. But the fire wasn't responding adequately.

Drawing partly on his experience fighting the 1957 Rocky Flats fire, the fire captain directed crews to use water. That decision helped bring the fire under control.

The filtration system was damaged

One of the most important questions was whether plutonium escaped the building.

Rocky Flats' ventilation system was designed to pull contaminated air through multiple stages of filtration before releasing it through exhaust stacks. During the 1969 fire, one booster filtration system became clogged, shifting airflow through another system. Later reconstruction found that the first two of four HEPA filter banks in that system were breached and gaskets in the remaining banks were also damaged. Electrical failure disabled some stack-sampling equipment at approximately 4 p.m. The surviving measurements and evidence collected after the fire allowed researchers decades later to reconstruct the likely release. Their estimate was not a single exact number. The Colorado Historical Public Exposures Study estimated that approximately 140 to 900 milligrams of plutonium — about 0.37 to 2.2 gigabecquerels — may have been released during the fire. As with the 1957 fire, uncertainty matters. Researchers were reconstructing an accident after the fact using incomplete measurements, historical records, contamination measurements and atmospheric modeling.

The fire that changed public awareness

The significance of May 11, 1969, extends beyond what happened inside Buildings 776/777.

Rocky Flats had already been producing nuclear weapons components for nearly two decades. Releases and accidents had occurred before, including the 1957 plutonium fire and contamination associated with leaking drums at the 903 Pad. But most Coloradans knew relatively little about what was happening inside the highly secretive facility.

A contemporary Rocky Mountain News report on May 12 told readers that a fire at Rocky Flats had released a small amount of plutonium contamination. Colorado's subsequent Historical Public Exposures materials describe the 1969 fire as the first time the public became generally aware of contaminant releases from Rocky Flats. That makes the fire an important dividing line in Rocky Flats history. There was the history of Rocky Flats that occurred largely outside public view. And there was the history that increasingly unfolded under public scrutiny.

What happened afterward

The accident also forced changes inside the plant. DOE's own historical account describes the 1969 fire as the costliest industrial accident in the United States at the time. Cleanup took approximately two years and involved around 600 workers. Afterward, Rocky Flats implemented significant new fire-safety measures, including additional firewalls and water sprinklers. DOE's history also states that plutonium work was thereafter to be conducted in an inert atmosphere to reduce the possibility of another plutonium fire. But the accident also intensified questions outside the plant. Scientists, public-health officials and community members increasingly began asking what contaminants had left Rocky Flats—not only during this fire, but throughout the plant's operating history. Those questions would eventually lead to environmental sampling, health studies, public controversy and, decades later, Colorado's comprehensive effort to reconstruct historical public exposures.

The 1957 and 1969 fires were not the same event

It's tempting to combine the two major Rocky Flats fires into a single story. They deserve to be understood separately. The 1957 fire involved Building 71, later called Building 771, and created an atmospheric release that Colorado's later reconstruction modeled as being transported toward Arvada and the Denver metropolitan area. The 1969 fire occurred in Buildings 776/777 under different meteorological conditions, with a different ventilation and filtration system and a different reconstructed pattern of potential off-site exposure.

They also occurred in very different public contexts. In 1957, Rocky Flats remained largely hidden behind Cold War secrecy. By 1969, metropolitan Denver had continued growing around the plant—and the Mother’s Day fire helped bring questions about Rocky Flats contamination into public view.

Why the 1969 fire still matters

The fire is more than an accident from Rocky Flats' past. It helps explain what happened next. It contributed to changes in fire protection at the plant. It drew public attention to the possibility that radioactive materials could leave the facility. And it helped generate questions about contamination beyond the plant boundary that Colorado scientists, public-health officials and residents would continue asking for decades. Those questions ultimately became part of the reason Colorado commissioned the Rocky Flats Historical Public Exposures Studies in the 1990s. The Colorado State Publications Library now preserves roughly 150 Rocky Flats-related documents, including specific reports on both the 1957 and 1969 fires, estimated airborne plutonium releases, historical emissions and public-health research. That historical record allows us to understand considerably more about the fire today than people living near Rocky Flats were told in 1969. And that may be one of the most important parts of this story.

Understanding Rocky Flats requires knowing not only what happened, but also what surrounding communities knew about it—and when they were finally able to begin asking questions.

Read the original sources

The Colorado State Publications Library's Rocky Flats Fires collection is particularly useful because it links directly to the state's 1969 Fire citizen summary, along with the technical report Estimated Airborne Releases of Plutonium During the 1969 Fire in Buildings 776-77 and related historical exposure studies.

The Colorado Historical Public Exposures Study — Technical Summary contains the state's reconstruction of both major fires. The Department of Energy Rocky Flats historical record provides DOE's account of the accident and subsequent safety changes.