Altair 4XR Care & Use
ALTAIR 4XR
What Does the Altair 4XR Detect?
Tracks flammable gases/vapours as a % of the Lower Explosive Limit.
Toxic, colourless and odourless combustion byproduct.
Identifies oxygen-deficient and oxygen-enriched atmospheres.
Highly toxic and flammable gas; detected in ppm.
MSA XCell digital sensor platform • rapid response • multi-modal alarms
Turning On the Altair 4XR
PRESS + HOLD CENTERHold until the unit sounds and the startup sequence begins.
Display segments illuminate • audible alarm • LEDs flash • vibration activates.
Startup data, software version, sensor information and alarm set points are displayed.
If FAS appears, confirm you are in clean air. Press center to accept or an arrow to skip.
Startup checks complete and the detector returns to live gas measurement.
Never accept Fresh Air Setup in a suspected contaminated atmosphere. The detector uses the current atmosphere as its zero reference.
End-of-Sensor-Life Heart Symbol
LIFE
After calibration, the heart icon may indicate an XCell sensor is nearing the end of its functional life. The sensor is typically still operational.
If span calibration fails because sensor output is too low, the heart symbol can appear with an error such as SPAN ERR. The sensor has reached end of useful life.
When the warning first appears, schedule sensor replacement promptly to avoid downtime. A short lead window may remain.
If the detector fails calibration with an end-of-life condition, remove it from service until the affected sensor is replaced and the detector passes calibration.
How to Change a Sensor
Turn the detector OFF. Remove the four rear case screws and carefully separate the case front.
Use fingers only. Gently rock the old sensor and pull it straight up from the socket. Inspect for corrosion or fluid leakage.
Align contact pins and the sensor tab with the holder. Press the replacement sensor firmly straight down.
Do not pry sensors out with screwdrivers or other tools.
Reassemble carefully, confirm gasket position, then perform a full calibration before returning the detector to service.
Sensors & Alarm Set Points
Low alarm = oxygen deficiency. High alarm = oxygen enrichment. Normal ambient air is approximately 20.9% O₂.
At 100% LEL (or about 5.0% methane by volume), the combustible channel enters a protective Lock Alarm. Leave the atmosphere and reset only in known fresh air.
“XXX” on the Screen — Lock Alarm
EXPLOSION HAZARD
The combustible reading has reached or exceeded the instrument’s full-scale limit — approximately 100% LEL / 5.0% CH₄ by volume.
Withdraw from the hazardous area and move to a confirmed fresh-air location.
When completely safe, power the detector off and back on to clear the lock condition.
“+++” on the Screen — Over-Range
A +++ indication means the actual gas concentration is higher than that sensor/channel can display numerically.
Treat an over-range combustible or toxic reading as an extreme hazard and move to clean, uncontaminated air.
The area must be properly tested, cleared and verified safe before crews return.
Sensor Measurement Ranges
0–100% LEL
(0–5.00% CH₄)
0–30.0% by volume
0–1,999 ppm
0–200 ppm
An over-range indication means the actual concentration may be higher than the detector can measure.
Over-Range Recovery — CO & H₂S
Move the detector into clean air and allow the CO and H₂S sensors to recover.
Perform a Fresh Air Setup (FAS) before returning the detector to normal use.
Leave the detector in clean air for a full 24 hours, then perform zero + span calibration.
+++ replaces the numerical value when a sensor is above full-scale range.
TWA & STEL — What Do They Mean?
Tracks your average toxic-gas exposure over an extended work period — typically an 8-hour shift.
Tracks a short-duration average exposure — typically 15 minutes — to warn about dangerous short-term spikes.
Four Alarm Types for Toxic Gases
Gas concentration reaches the programmed low alarm set point.
Gas concentration reaches the programmed high alarm set point.
A short-duration exposure average reaches the STEL limit (15-minute average).
The time-weighted average exposure reaches the TWA limit (8-hour workday).
Monitoring Oxygen Concentrations
The 4XR continuously measures oxygen in the surrounding atmosphere.
Below 19.5% O₂ is an oxygen-deficient atmosphere and requires immediate attention.
Ambient air is approximately 20.8% O₂. Use this as a field reference — not as a replacement for the instrument.
Higher-than-normal oxygen increases fire intensity and ignition risk. A common high alarm is 23.0% O₂.
Measurement capability extends to 30% O₂; follow instrument approvals and your department SOPs.
Alarm Indicators & Screen Symbols
GX2 Automated Test Stand & Calibration Gas
Automates bump testing, calibration and record keeping for compatible MSA detectors.
REPEATABLE
DOCUMENTED
Combustible gas = 1.45% methane by volume, used as a 58% LEL pentane simulant. Balance gas: nitrogen.
Methane is stable in the cylinder and provides a practical, repeatable way to calibrate the combustible sensor to the intended pentane response curve without handling heavier hydrocarbon vapours.
LEL % — How the Math Works
Therefore, 1% LEL of methane ≈ 500 ppm.
Important: each combustible gas has a different LEL. The conversion is gas-specific.
Performing a Sensor Refresh / Zero Calibration
Move to a verified clean-air location. Keep calibration gas and adapters away from the instrument during the zero.
Let the Altair 4XR complete its normal startup and self-check sequence.
Enter the calibration menu until the display shows ZERO CAL?.
Confirm the zero calibration and sensor refresh.
ZERO PASS = successful. ZERO ERR = the affected sensor did not zero correctly.
Never zero the detector in contaminated air — it can create an incorrect baseline and compromise later readings.
Fresh Air Setup (FAS) Without Turning the Unit Off
Move to clean, uncontaminated air.
Press and hold UP for ~3 seconds.
Wait for the FAS? prompt.
Press the center button promptly.
Unit zeros sensors and returns to live readings.
Do not use FAS as a workaround for an alarm. If gas is present, performing FAS can incorrectly treat the current atmosphere as zero. Move to verified fresh air first.
FAS ERR means the sensor baseline could not be cleared. Remove the instrument from normal service and perform a full calibration before return to use.
Forcing a Calibration Using the GX2
Automated test stand
Why Does the Gas Company Detect Gas When We Don’t?
Altair 4XR displays combustible gas in 1% LEL increments.
For methane:
100 ppm methane = 0.2% LEL → the display may still read 0% LEL.
High-sensitivity leak detectors can read much smaller methane concentrations — often in ppm.
Different sensor technologies are optimized for different tasks.
0% LEL does not necessarily mean zero natural gas is present.
Different Meters. Different Missions.
Life safety • atmospheric hazard assessment • tactical decisions
% LEL — proximity to a flammable / explosive atmosphere
No measurable %LEL concentration is being displayed at that sampling point and time.
Leak location • isolation • infrastructure repair
PPM / high sensitivity — find very small methane releases
They may keep searching until the local background is confirmed clean and the leak source is located.
LEL Tactical Thresholds
Significant combustible-gas condition. Control ignition sources, reassess conditions and use department SOPs to guide continued operations.
Rapidly increasing hazard. Withdraw to a safer position and reassess. Remember that gas can stratify or pocket unevenly.
At the lower explosive limit. Expect over-range / lock alarm. Leave the atmosphere and reset only in known fresh air.
A.J. STONE COMPANY LTD. • FIRE SERVICE TRAINING