The purpose of this study is to analyze the diffusion behavior of aldehyde in the air under hypothetical scenarios of formalin leakage during the use of this hazardous substance in laboratories. Based on the findings, permissible handling limits for safe use are proposed. The time required to reach the Immediately Dangerous to Life or Health (IDLH) concentration of 20 ppm, as defined by the National Institute for Occupational Safety and Health (NIOSH), was calculated according to the amount of formalin leakage. In a 150 ㎡ laboratory, it was observed that IDLH was reached within 8.6 seconds for a leakage of 250 ml, 2.2 seconds for 1000 ml, and 0.5 seconds for 4000 ml. Even in laboratories equipped with local exhaust ventilation systems, hazardous substances were found to linger due to various factors. Notably, when the air supply vent was located above the local exhaust system and the exhaust vent was positioned above the workbench, formalin vapor rising from the floor showed no reduction in concentration at the researcher’s breathing zone. This study aims to enhance the safety and health standards for laboratory personnel by proposing appropriate handling limits and safety equipment guidelines to ensure safety in various laboratory settings in the event of formalin leakage.