Is there a time limitation for wearing the Dorma 99 respirator?

Recommended Dorma 99 wearing time

Dorma Filtration recommends a maximum time frame of 4-6 hours to sustain comfort and breathability.

DO NOT use the Dorma 99 respirator continuously for more than 8 hours. In heavily contaminated or humid environments the respirator may reach its filtration load more rapidly.
The user must be aware of the respirator’s filter load throughout use. If breathing becomes difficult, immediately leave the contaminated area and don a new/clean Dorma 99 respirator.