The Chernobyl nuclear accident in 1986 led to an urgent need for protection of workers from radioactive aerosols. Approximately 300,000 negative pressure filtering facepieces of the model "Lepestok" were sent to Chernobyl in June 1986. These respirators were considered to be very effective (the declared protection factor for the most common model was 200). However, the individuals who used these respirators were exposed to excessive contamination. Just as in the case of the studies noted above, the declared protection factor was very different from the actual protection factor under real-world conditions. As seen in other workplace tests, the passage of unfiltered air through the gap between the mask and face undermined the efficiency of the respirator. However, these discoveries did not lead to a change in assessments of the effectiveness of respirators in the USSR.