Level X1 · Breathing endurance
NO LIMIT
Neutral comfort — resistance not perceptible
New respirator · Within the manufacturer's stated conditions of use
What it means
The resistance is not perceptible.
At this level the mask adds a resistance you cannot feel. Breathing through it is, for the airways, the same as breathing without it. This is the only level suitable without restriction for children, elderly people and people with reduced respiratory capacity, and for sleep.
Continuous wear without time limit, including for sensitive groups (children, elderly people, people with reduced respiratory capacity) and during sleep.
- Specific resistance
- ≤ 30 Pa/(L·s⁻¹)
- Comfort qualification
- Neutral comfort — resistance not perceptible
- Reference state
- New respirator, unworn, taken out of its original packaging for the test, measured on a constant-flow bench
Where the boundary comes from
No threshold is set by convention.
The X1/X2 boundary is set at half the lower bound of the detection threshold of added inspiratory resistance, as a safety margin for people whose perception threshold is lowered.
Same level, four situations
The level does not change with effort; what you feel does.
Specific resistance is invariant, so a mask keeps its level whatever the activity. But the pressure the wearer actually overcomes grows with the breathing flow, and the work of breathing grows with its square: a mask that is comfortable at rest becomes demanding in fast walking without having changed nature.
| Profile | Situation | Bench flow | Δp at X1 (Pa) |
|---|---|---|---|
| P1 | Rest, seated | 30 L/min | 0 – 15 |
| P2 | Light to moderate activity | 60 L/min | 0 – 30 |
| P3 | Sustained occupational effort | 95 L/min | 0 – 48 |
| P4 | Intense, sporting effort | 140 L/min | 0 – 70 |
What the level does not say
How long you can actually wear the mask is the smallest of several limits. This level sets one of them.
- Breathing enduranceSet by the resistance of the device. This is the object of the XRS scale.
- Clogging of the filterResistance rises as particles accumulate, at a rate that depends on the working atmosphere.
- Exhaled moistureLoads the media, alters the fit and favours microbial growth.
- Surface hygieneThe outer surface is contaminated by deposit and by handling.
- Fit over timeDegrades with handling and the loosening of the straps.
- The manufacturer's instructionsPrevail over everything else — notably the NR marking limiting use to a single work shift.
The XRS level qualifies breathing comfort. It does not qualify filtration efficiency: the protection of a mask is declared separately, under the applicable standard. The level describes a new mask; it never authorizes use beyond the manufacturer's conditions.
The other levels