Harry Daghlian was a physicist working on the Manhattan Project at Los Alamos National Laboratory. The project was critical for the development of atomic weapons during World War II. Daghlian was involved in experiments to determine the properties of a plutonium core known as the Demon core, which was intended for use in future nuclear devices. On August 21, while attempting to create a neutron-reflecting configuration using tungsten carbide bricks, Daghlian inadvertently dropped a brick that led to an uncontrolled reaction. This criticality accident resulted in a flash of intense radiation, which exposed Daghlian to a lethal dose. After the accident, he experienced severe radiation sickness, which resulted in his eventual death less than a month later.

The Demon core was later involved in another fatal incident that occurred during separate experiments with a physicist named Louis Slotin, leading to enhanced safety protocols in nuclear research. The circumstances surrounding Daghlian's work exemplified the perilous nature of early nuclear experiments, where safety procedures were not well understood. This event underscored the importance of safety measures and awareness in laboratories handling radioactive materials.

Daghlian's accident and the subsequent analysis of the incident played a crucial role in shaping safety protocols in nuclear physics, ultimately leading to a more cautious approach in the handling of nuclear materials. The lessons learned from his and Slotin's fatalities led to improved training and clearer guidelines for laboratory safety, influencing future research practices.