{"product_id":"watchgas-replacement-so2-sensor-sst-spare-s","title":"WatchGas Replacement SO2 Sensor SST-SPARE-S","description":"\u003cp\u003e\u003cstrong\u003eWhen your SO2 sensor drifts, you don't replace the whole monitor. You swap the sensor cell.\u003c\/strong\u003e\u003c\/p\u003e\n\n\u003cp\u003eThat'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 \u003ca href=\"https:\/\/pksafety.com\/products\/watchgas-sst1-serviceable-so2-gas-detector-sst1-s\"\u003eWatchGas SST1-S Serviceable SO2 Gas Detector\u003c\/a\u003e and any WatchGas SST4-series multi-gas monitor configured with an SO2 sensor slot.\u003c\/p\u003e\n\n\u003cp\u003e\u003cstrong\u003eSmell isn't a reliable backup when your SO2 sensor drifts.\u003c\/strong\u003e 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.\u003c\/p\u003e\n\n\u003cp\u003e\u003cstrong\u003eWhat this sensor is (and isn't):\u003c\/strong\u003e\u003c\/p\u003e\n\u003cul\u003e\n\u003cli\u003e\n\u003cstrong\u003eIt IS\u003c\/strong\u003e 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 \u003cem\u003estandard\u003c\/em\u003e 4-gas sensor set is LEL\/O2\/CO\/H2S — SO2 is a custom configuration on SST4 monitors, not the default.\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eIt is NOT\u003c\/strong\u003e compatible with the Limited-Life \u003ca href=\"https:\/\/pksafety.com\/products\/watchgas-sst1-2-year-so2-gas-detector-sst1-s-24\"\u003eSST1-S-24 (2-year)\u003c\/a\u003e 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).\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eIt is NOT\u003c\/strong\u003e a standalone gas detection device. The sensor cell requires a compatible WatchGas SST monitor to function.\u003c\/li\u003e\n\u003c\/ul\u003e\n\n\u003cp\u003e\u003cstrong\u003eSolid polymer electrochemical sensor technology.\u003c\/strong\u003e 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.\u003c\/p\u003e\n\n\u003cp\u003e\u003cstrong\u003eWhen to replace an SO2 sensor cell:\u003c\/strong\u003e\u003c\/p\u003e\n\u003cul\u003e\n\u003cli\u003eThe sensor fails a bump test and won't recover on recalibration\u003c\/li\u003e\n\u003cli\u003eCalibration 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\u003c\/li\u003e\n\u003cli\u003eThe monitor displays a sensor fault code specific to the SO2 channel\u003c\/li\u003e\n\u003cli\u003eThe sensor's warranty period (2 years) has elapsed and calibration reliability starts trending down\u003c\/li\u003e\n\u003cli\u003eYou'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\u003c\/li\u003e\n\u003c\/ul\u003e\n\n\u003cp\u003e\u003cstrong\u003eWho buys the SST-SPARE-S:\u003c\/strong\u003e\u003c\/p\u003e\n\u003cul\u003e\n\u003cli\u003eOwners of the WatchGas SST1-S serviceable SO2 monitor whose current sensor has drifted, failed a bump, or reached end-of-warranty\u003c\/li\u003e\n\u003cli\u003eOwners of WatchGas SST4-MINI, SST4-MICRO, or SST4-PUMP multi-gas monitors that were \u003cem\u003ecustom-configured\u003c\/em\u003e with an SO2 sensor slot (not the standard LEL\/O2\/CO\/H2S set)\u003c\/li\u003e\n\u003cli\u003eRefinery operators handling sour crude, hydrotreating, or sulfur recovery units\u003c\/li\u003e\n\u003cli\u003ePulp and paper mill supervisors running Kraft-process campaigns or on-site sulfur recovery inspections\u003c\/li\u003e\n\u003cli\u003eMetal smelter operations (copper, zinc, lead) maintaining continuous SO2 monitoring\u003c\/li\u003e\n\u003cli\u003eSulfuric acid manufacturing plants running ongoing exposure programs\u003c\/li\u003e\n\u003cli\u003eCoal-fired power plant operators monitoring boiler-outlet and stack SO2\u003c\/li\u003e\n\u003cli\u003eIndustrial boiler and combustion equipment operators\u003c\/li\u003e\n\u003cli\u003eMining and mineral processing operations with sulfide ore roasting\u003c\/li\u003e\n\u003c\/ul\u003e\n\n\u003cp\u003e\u003cstrong\u003eSensor specifications:\u003c\/strong\u003e\u003c\/p\u003e\n\u003ctable\u003e\n\u003ctbody\u003e\n\u003ctr\u003e\n\u003ctd\u003e\u003cstrong\u003eGas\u003c\/strong\u003e\u003c\/td\u003e\n\u003ctd\u003e\u003cstrong\u003eSensor technology\u003c\/strong\u003e\u003c\/td\u003e\n\u003ctd\u003e\u003cstrong\u003eWarranty\u003c\/strong\u003e\u003c\/td\u003e\n\u003ctd\u003e\u003cstrong\u003eCompatible monitors\u003c\/strong\u003e\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr\u003e\n\u003ctd\u003eSO2 (sulfur dioxide)\u003c\/td\u003e\n\u003ctd\u003eSolid polymer electrochemical (dry-cell)\u003c\/td\u003e\n\u003ctd\u003e2 years\u003c\/td\u003e\n\u003ctd\u003eSST1-S, SST4-series (with SO2 sensor slot configuration)\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003c\/tbody\u003e\n\u003c\/table\u003e\n\n\u003cp\u003e\u003cstrong\u003eKey features:\u003c\/strong\u003e\u003c\/p\u003e\n\u003cul\u003e\n\u003cli\u003eHigh accuracy across the full detection range\u003c\/li\u003e\n\u003cli\u003eLong operational lifetime — 2-year warranty\u003c\/li\u003e\n\u003cli\u003eUltra-low power consumption (optimized for battery-operated and IoT-integrated monitors)\u003c\/li\u003e\n\u003cli\u003eHigh precision at low SO2 concentrations — critical for NIOSH REL-aligned monitoring (2 ppm TWA \/ 5 ppm STEL)\u003c\/li\u003e\n\u003cli\u003eNo zero drift\u003c\/li\u003e\n\u003cli\u003eSilicone-resistant (no poisoning by common industrial silicone contaminants)\u003c\/li\u003e\n\u003cli\u003eDirect linearity across the detection range\u003c\/li\u003e\n\u003cli\u003eHigh temperature range tolerance\u003c\/li\u003e\n\u003c\/ul\u003e\n\n\u003cp\u003e\u003cstrong\u003ePK Safety services the full WatchGas SST line with factory-trained technicians in-house.\u003c\/strong\u003e 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 \u003cstrong\u003e800.829.9580\u003c\/strong\u003e to talk through your SO2 sensor replacement workflow with someone who understands the SST1 \/ SST4 platform.\u003c\/p\u003e\n\n\u003cdiv class=\"specification\"\u003e\n\u003cp\u003e\u003cstrong\u003eTechnical documents (WatchGas SST1):\u003c\/strong\u003e\u003c\/p\u003e\n\u003cp\u003e\u003ca href=\"https:\/\/watchgas.com\/app\/uploads\/2024\/03\/SST1-brochure-1.1.pdf\" target=\"_blank\"\u003e\u003cimg border=\"0\" height=\"65\" width=\"63\" alt=\"Brochure\" src=\"https:\/\/cdn.shopify.com\/s\/files\/1\/0872\/5469\/6254\/files\/pdf-icon_ac4da377-e8e0-4a9c-9dcc-746269055096.png\"\u003e\u003c\/a\u003e \u003cstrong\u003eSST1 Brochure\u003c\/strong\u003e\u003c\/p\u003e\n\u003c\/div\u003e\n\n\u003cp\u003e\u003cstrong\u003ePart Number:\u003c\/strong\u003e WG01-SST-SPARE-S — WatchGas Replacement SO2 Sensor (2-year warranty)\u003c\/p\u003e\n\n\u003ch2\u003eFrequently Asked Questions\u003c\/h2\u003e\n\n\u003cdetails open\u003e\n\u003csummary\u003eWhich WatchGas monitors is the SST-SPARE-S sensor compatible with?\u003c\/summary\u003e\n\u003cp\u003eThe SST-SPARE-S is compatible with:\u003c\/p\u003e\n\u003cul\u003e\n\u003cli\u003e\n\u003ca href=\"https:\/\/pksafety.com\/products\/watchgas-sst1-serviceable-so2-gas-detector-sst1-s\"\u003eSST1-S Serviceable SO2 Gas Detector\u003c\/a\u003e — the single-gas SO2 monitor is designed around this sensor\u003c\/li\u003e\n\u003cli\u003eWatchGas SST4-series multi-gas monitors (\u003ca href=\"https:\/\/pksafety.com\/products\/watchgas-sst4-mini-diffusion-4-gas-detector\"\u003eSST4-MINI\u003c\/a\u003e, \u003ca href=\"https:\/\/pksafety.com\/products\/watchgas-sst4-micro-diffusion-4-gas-detector\"\u003eSST4-MICRO\u003c\/a\u003e, \u003ca href=\"https:\/\/pksafety.com\/products\/watchgas-sst4-pump-4-gas-detector\"\u003eSST4-PUMP\u003c\/a\u003e) \u003cstrong\u003eonly when custom-configured with an SO2 sensor slot\u003c\/strong\u003e\n\u003c\/li\u003e\n\u003c\/ul\u003e\n\u003cp\u003eThe SST4 platform's \u003cem\u003estandard\u003c\/em\u003e 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.\u003c\/p\u003e\n\u003cp\u003eThe SST-SPARE-S is NOT compatible with the Limited-Life \u003ca href=\"https:\/\/pksafety.com\/products\/watchgas-sst1-2-year-so2-gas-detector-sst1-s-24\"\u003eSST1-S-24 (2-year)\u003c\/a\u003e alert-only monitor — that one is non-serviceable by design. There is no 3-year alert-only SO2 variant in the SST1 line.\u003c\/p\u003e\n\u003c\/details\u003e\n\n\u003cdetails open\u003e\n\u003csummary\u003eHow do I know it's time to replace my SO2 sensor?\u003c\/summary\u003e\n\u003cp\u003eFour common signals:\u003c\/p\u003e\n\u003col\u003e\n\u003cli\u003e\n\u003cstrong\u003eThe sensor fails a bump test\u003c\/strong\u003e 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.\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eCalibration drift exceeds acceptable tolerance\u003c\/strong\u003e 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.\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eThe monitor displays a sensor fault code\u003c\/strong\u003e specific to the SO2 channel. Cell exhaustion, extreme temperature or humidity exposure, or physical damage can trigger a fault.\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eThe sensor is out of its warranty period.\u003c\/strong\u003e The SST-SPARE-S 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.\u003c\/li\u003e\n\u003c\/ol\u003e\n\u003c\/details\u003e\n\n\u003cdetails open\u003e\n\u003csummary\u003eWhy does SO2 sensor drift matter more than drift on other gases?\u003c\/summary\u003e\n\u003cp\u003eBecause 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.\u003c\/p\u003e\n\u003cp\u003eThat 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.\u003c\/p\u003e\n\u003cp\u003eProactive sensor replacement is worth the discipline for SO2 more than for gases where sensory backup provides real cover.\u003c\/p\u003e\n\u003c\/details\u003e\n\n\u003cdetails open\u003e\n\u003csummary\u003eCan I install the SST-SPARE-S myself, or do I need to send the monitor to PK Safety?\u003c\/summary\u003e\n\u003cp\u003eBoth 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.\u003c\/p\u003e\n\u003cp\u003eIf 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.\u003c\/p\u003e\n\u003c\/details\u003e\n\n\u003cdetails open\u003e\n\u003csummary\u003eShould I replace the sensor or buy a new SST1-S monitor?\u003c\/summary\u003e\n\u003cp\u003eThe SST-SPARE-S 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 \u003ca href=\"https:\/\/pksafety.com\/products\/watchgas-sst1-serviceable-so2-gas-detector-sst1-s\"\u003eSST1-S monitor\u003c\/a\u003e costs $290. Sensor swap saves you $110 vs. a full new monitor — roughly 62% of the full-monitor price for the maintenance action.\u003c\/p\u003e\n\u003cp\u003eThe 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.\u003c\/p\u003e\n\u003c\/details\u003e\n\n\u003cdetails open\u003e\n\u003csummary\u003eHow is the SST-SPARE-S calibrated after installation?\u003c\/summary\u003e\n\u003cp\u003eAfter 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.\u003c\/p\u003e\n\u003cp\u003eAutomated calibration is fastest using the \u003ca href=\"https:\/\/pksafety.com\/products\/watchgas-docking-station-w-touchscreen-sst-dock\"\u003eWatchGas SST-DOCK Touchscreen docking station\u003c\/a\u003e — one docking cycle handles bump test and full calibration in about 60 seconds. Manual calibration through the monitor's menu also works.\u003c\/p\u003e\n\u003c\/details\u003e\n\n\u003cp\u003e\u003cstrong\u003eNot 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.\u003c\/strong\u003e A person who knows the SST platform's service ecosystem will pick up.\u003c\/p\u003e","brand":"WatchGas","offers":[{"title":"Default Title","offer_id":52671728058735,"sku":"WG01-SST-SPARE-S","price":180.0,"currency_code":"USD","in_stock":true}],"thumbnail_url":"\/\/cdn.shopify.com\/s\/files\/1\/0872\/5469\/6254\/files\/SST-SPARE-S---Watchgas-SST-sensor-SO2-0-50ppm-for-all---1---K1E800x800compressed.jpg?v=1771008066","url":"https:\/\/pksafety.com\/products\/watchgas-replacement-so2-sensor-sst-spare-s","provider":"PK Safety Supply","version":"1.0","type":"link"}