Level X2 · Breathing endurance
ALL DAY
High comfort — at the limit of perception
New respirator · Within the manufacturer's stated conditions of use
What it means
The resistance is at the limit of perception.
At this level the resistance stays at the limit of what a healthy adult perceives. The mask can be worn a whole day — office, school, shop, transport — without the resistance itself calling for a break. Most well-designed disposable respirators on the market fall here.
Continuous wear over a full day without imposed breaks: office, school, retail, transport, urban travel.
- Specific resistance
- 30 – 60 Pa/(L·s⁻¹)
- Comfort qualification
- High comfort — at the limit of perception
- 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 X2/X3 boundary, at 60 Pa/(L·s⁻¹), is the lower bound of the psychophysical detection threshold measured in the literature (58,8–74,5), rounded down by prudence. It is the best-supported boundary of the scale.
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 X2 (Pa) |
|---|---|---|---|
| P1 | Rest, seated | 30 L/min | 15 – 30 |
| P2 | Light to moderate activity | 60 L/min | 30 – 60 |
| P3 | Sustained occupational effort | 95 L/min | 48 – 95 |
| P4 | Intense, sporting effort | 140 L/min | 70 – 140 |
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