SKU: WG01-SST-S-RPL

WatchGas Replacement SO2 Sensor SST-S-RPL

$180.00

Ships in 2 - 3 weeks

Description

When your SO2 sensor drifts, you don't replace the whole monitor. You swap the sensor cell.

That's the operational advantage of the serviceable WatchGas SST1 line. Traditional single-gas monitors are single-use — when the sensor reaches end-of-life or a bump test reveals unrecoverable drift, the whole unit gets discarded. The SST1 platform is designed to be maintained: this WatchGas Replacement SO2 Sensor drops into the WatchGas SST1-S Serviceable SO2 Gas Detector and any WatchGas SST4-series multi-gas monitor configured with an SO2 sensor slot.

Smell isn't a reliable backup when your SO2 sensor drifts. Sulfur dioxide has a pungent, unmistakable odor that most workers detect between 0.5 and 3 ppm. OSHA's permissible exposure limit is 5 ppm 8-hour TWA (29 CFR 1910.1000 Table Z-1), and NIOSH's more conservative REL is 2 ppm TWA plus a 5 ppm STEL. The range where you can smell SO2 overlaps the exposure limit — workers might notice a leak AT the limit, but not below it. A drifting SO2 sensor doesn't just mean a lagging alarm; it means workers may be exposed at NIOSH's TWA before they smell anything, and at OSHA's PEL before smell becomes strong enough to command attention. Sensor accuracy at low SO2 concentrations is the point of the monitor.

What this sensor is (and isn't):

It IS a factory replacement SO2 electrochemical sensor cell for the serviceable SST1-S monitor and any WatchGas SST4-series multi-gas monitor that was configured with an SO2 sensor slot. Note that the SST4 platform's standard 4-gas sensor set is LEL/O2/CO/H2S — SO2 is a custom configuration on SST4 monitors, not the default.
It is NOT compatible with the Limited-Life SST1-S-24 (2-year) alert-only monitor — that one is non-serviceable by design and is discarded at end-of-life. There is no 3-year alert-only SO2 variant in the SST1 line (two-tier SO2 product family, same structure as O2).
It is NOT a standalone gas detection device. The sensor cell requires a compatible WatchGas SST monitor to function.

Solid polymer electrochemical sensor technology. The dry-cell design eliminates the liquid electrolyte used in traditional electrochemical sensors, giving the cell better long-term stability, no leak risk in truck-bed or field storage, and better tolerance for temperature extremes. Ultra-low power consumption compared to older SO2 sensor designs.

When to replace an SO2 sensor cell:

The sensor fails a bump test and won't recover on recalibration
Calibration drift exceeds acceptable tolerance across successive cal events, especially at the low end of the detection range where the OSHA PEL and NIOSH REL sit
The monitor displays a sensor fault code specific to the SO2 channel
The sensor's warranty period (2 years) has elapsed and calibration reliability starts trending down
You're rotating a fleet's sensor generation on a proactive maintenance cadence — especially valuable in refinery, pulp mill, and smelter environments where SO2 exposure is continuous

Who buys the SST-S-RPL:

Owners of the WatchGas SST1-S serviceable SO2 monitor whose current sensor has drifted, failed a bump, or reached end-of-warranty
Owners of WatchGas SST4-MINI, SST4-MICRO, or SST4-PUMP multi-gas monitors that were custom-configured with an SO2 sensor slot (not the standard LEL/O2/CO/H2S set)
Refinery operators handling sour crude, hydrotreating, or sulfur recovery units
Pulp and paper mill supervisors running Kraft-process campaigns or on-site sulfur recovery inspections
Metal smelter operations (copper, zinc, lead) maintaining continuous SO2 monitoring
Sulfuric acid manufacturing plants running ongoing exposure programs
Coal-fired power plant operators monitoring boiler-outlet and stack SO2
Industrial boiler and combustion equipment operators
Mining and mineral processing operations with sulfide ore roasting

Sensor specifications:

Gas	Sensor technology	Warranty	Compatible monitors
SO2 (sulfur dioxide)	Solid polymer electrochemical (dry-cell)	2 years	SST1-S, SST4-series (with SO2 sensor slot configuration)

Key features:

High accuracy across the full detection range
Long operational lifetime — 2-year warranty
Ultra-low power consumption (optimized for battery-operated and IoT-integrated monitors)
High precision at low SO2 concentrations — critical for NIOSH REL-aligned monitoring (2 ppm TWA / 5 ppm STEL)
No zero drift
Silicone-resistant (no poisoning by common industrial silicone contaminants)
Direct linearity across the detection range
High temperature range tolerance

PK Safety services the full WatchGas SST line with factory-trained technicians in-house. If you'd rather send the monitor to us for sensor replacement than swap the cell yourself, we handle that in-house — full swap, calibration verification against a certified SO2 standard, and return-to-service. We also service BW/Honeywell (Factory Authorized Service Center), RKI, and RAE Systems monitors — one shop for a mixed-brand fleet's sensor lifecycle. Call us at 800.829.9580 to talk through your SO2 sensor replacement workflow with someone who understands the SST1 / SST4 platform.

Technical documents (WatchGas SST1):

SST1 Brochure

Part Number: WG01-SST-S-RPL — WatchGas Replacement SO2 Sensor (2-year warranty)

Frequently Asked Questions

Which WatchGas monitors is the SST-S-RPL sensor compatible with?

The SST-S-RPL is compatible with:

SST1-S Serviceable SO2 Gas Detector — the single-gas SO2 monitor is designed around this sensor
WatchGas SST4-series multi-gas monitors (SST4-MINI, SST4-MICRO, SST4-PUMP) only when custom-configured with an SO2 sensor slot

The SST4 platform's standard 4-gas sensor set is LEL/O2/CO/H2S. If your SST4 monitor was ordered with the standard configuration, it doesn't have an SO2 slot and this sensor won't fit. If your SST4 was custom-configured with SO2 replacing one of the standard four gases (usually H2S is swapped out in favor of SO2 for refinery-specific work), then this sensor is the right replacement. Not sure which configuration your SST4 has? Call PK Safety at 800.829.9580 with your monitor's serial number.

The SST-S-RPL is NOT compatible with the Limited-Life SST1-S-24 (2-year) alert-only monitor — that one is non-serviceable by design. There is no 3-year alert-only SO2 variant in the SST1 line.

How do I know it's time to replace my SO2 sensor?

Four common signals:

The sensor fails a bump test and won't recover after recalibration. Bump testing before each use is the industry-standard way to verify sensor response; a persistent bump failure means the sensor cell is no longer detecting reliably.
Calibration drift exceeds acceptable tolerance across successive cal events, especially at the low end of the detection range — the concentrations where the OSHA PEL and NIOSH REL sit. A sensor that drifts high at 2 ppm is missing the NIOSH threshold.
The monitor displays a sensor fault code specific to the SO2 channel. Cell exhaustion, extreme temperature or humidity exposure, or physical damage can trigger a fault.
The sensor is out of its warranty period. The SST-S-RPL carries a 2-year warranty. Beyond that, sensor reliability trends down and proactive replacement is best practice — especially in continuous SO2 environments like refineries, mills, and smelters where sensor drift is the difference between compliance and a missed exposure.

Why does SO2 sensor drift matter more than drift on other gases?

Because SO2's odor detection threshold overlaps the OSHA exposure limit. Most workers can smell sulfur dioxide between 0.5 and 3 ppm — but OSHA's PEL is 5 ppm 8-hour TWA, and NIOSH's REL is stricter at 2 ppm TWA plus 5 ppm STEL. The range where smell registers is the same range where you're already at or approaching the exposure limit.

That physiology has one operational implication for SO2 monitoring: smell is NOT a reliable early-warning backup when the monitor drifts. Unlike H2S (which registers as rotten-egg smell well below the exposure limit and provides some sensory redundancy), SO2 gives workers a warning only AT the compliance threshold, not below it. If the SO2 sensor drifts high and no longer alarms at 2 ppm or 5 ppm, workers won't feel a substitute warning until they're already breathing at or above the PEL.

Proactive sensor replacement is worth the discipline for SO2 more than for gases where sensory backup provides real cover.

Can I install the SST-S-RPL myself, or do I need to send the monitor to PK Safety?

Both paths work. The SST1 platform is designed for user sensor replacement — the sensor cell is accessed through the monitor's service compartment, and the WatchGas SST1 manual walks through the swap procedure. After installation, you'll need to complete a full calibration to verify the new sensor's response against a known SO2 standard.

If you'd rather not run the swap yourself, or if you want a factory-trained technician to verify the sensor's performance across its full range before it goes back into service, send the monitor to PK Safety. We handle the swap, full calibration verification, and return-to-service in-house.

Should I replace the sensor or buy a new SST1-S monitor?

The SST-S-RPL sensor cell costs $180 — slightly higher than the other RPL sensors in the WatchGas SST line ($160 baseline) because the sulfur-tolerant electrochemical cell is a premium component. A full new SST1-S monitor costs $290. Sensor swap saves you $110 vs. a full new monitor — roughly 62% of the full-monitor price for the maintenance action.

The sensor replacement is the more cost-effective path when your monitor's housing, display, battery, and electronics are in good working order and only the SO2 sensor has drifted. The full-monitor replacement is a better fit when the monitor itself is aging, has physical damage, or has a battery that no longer holds charge. Call PK Safety at 800.829.9580 with your monitor's condition and we'll walk you through the choice.

How is the SST-S-RPL calibrated after installation?

After installing the new sensor cell in the monitor, run a full calibration cycle using an SO2 calibration gas standard — typically 10 ppm SO2 in nitrogen or air balance. Sulfur dioxide cal gas is corrosive and reactive, so use a stainless-steel or nickel-plated regulator (not brass) and dedicated Teflon or Tygon tubing that won't degrade over time.

Automated calibration is fastest using the WatchGas SST-DOCK Touchscreen docking station — one docking cycle handles bump test and full calibration in about 60 seconds. Manual calibration through the monitor's menu also works.

Not sure whether your SST4 has an SO2 sensor slot, or whether a swap or full monitor replacement is the right path? Call PK Safety at 800.829.9580. A person who knows the SST platform's service ecosystem will pick up.