Level X5 · Breathing endurance
UNDER 1 HOUR
Constrained comfort — established breathing discomfort
New respirator · Within the manufacturer's stated conditions of use
What it means
Breathing discomfort is established.
At this level breathing discomfort is established. The mask is worn in short sequences of less than one hour, with mandatory breaks, by a trained wearer on a supervised task. It remains the right choice for a short intervention in a loaded atmosphere; it is not suitable for prolonged wear.
Wear in short sequences, under one hour, with mandatory breaks. Trained subject, supervised task.
- Specific resistance
- 140 – 200 Pa/(L·s⁻¹)
- Comfort qualification
- Constrained comfort — established breathing 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 X5/X6 boundary, at 200 Pa/(L·s⁻¹), is the resistance ceiling of the highest filtration class. Independently, the physiological limits of ISO 16976-4, converted to specific resistance, give 208 and 218 at the highest sustained work rate: two reasonings with nothing in common designate the same boundary.
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 X5 (Pa) |
|---|---|---|---|
| P1 | Rest, seated | 30 L/min | 70 – 100 |
| P2 | Light to moderate activity | 60 L/min | 140 – 200 |
| P3 | Sustained occupational effort | 95 L/min | 222 – 317 |
| P4 | Intense, sporting effort | 140 L/min | 327 – 467 |
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