Level X3 · Breathing endurance
SEVERAL HOURS
Ordinary comfort — perceptible, without discomfort
New respirator · Within the manufacturer's stated conditions of use
What it means
The resistance is perceptible, without discomfort.
At this level you feel the mask when you breathe, without it being unpleasant. It suits several hours of active work — standing, light handling, brisk walking — with the natural breaks of a working day. At rest the effort is slight; it becomes distinct during sustained physical effort.
Wear of several hours interspersed with natural breaks: active standing work, light handling, brisk walking.
- Specific resistance
- 60 – 100 Pa/(L·s⁻¹)
- Comfort qualification
- Ordinary comfort — perceptible, without discomfort
- 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 X3/X4 boundary, at 100 Pa/(L·s⁻¹), is the exit of the detection band (74,5) increased by the uncertainty margin, in the vicinity of the most demanding published breathability ceiling (103,8). Beyond it, resistance is no longer merely perceived: it is endured.
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 X3 (Pa) |
|---|---|---|---|
| P1 | Rest, seated | 30 L/min | 30 – 50 |
| P2 | Light to moderate activity | 60 L/min | 60 – 100 |
| P3 | Sustained occupational effort | 95 L/min | 95 – 158 |
| P4 | Intense, sporting effort | 140 L/min | 140 – 233 |
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