1. The mask is contaminated with foreign bodies such as blood stains or droplets. 2. The user feels increased respiratory resistance. 3. Damaged masks. 4. Dustproof filter cotton: under the condition that the mask fits well with the user's face, when the user feels great respiratory...https://www.rollmed.net/face-mask/oxygen-mask-concentration.html
Oxygen Mask Concentration
Spedito - 15/11/2020 : 20:40:25
