Hydrogen Cyanide Sensors
Select HCN sensors for personal safety, firefighting, emergency response, petrochemical plants, mining, electroplating, pharmaceutical production and fixed industrial monitoring. Compare electrochemical range, response time, bias requirements, cross-sensitivity and exposure-life limits.
HCN measurement needs useful resolution well below full scale
Hydrogen cyanide is an acute toxic hazard. NIOSH lists a short-term recommended exposure limit of 4.7 ppm and an IDLH value of 50 ppm. These values are exposure references rather than universal gas-detector alarm setpoints, but they show why a 0–100 ppm sensor still needs reliable low-ppm behavior.
Short-term exposure reference with a skin notation.
Immediately Dangerous to Life or Health reference value.
Typical electrochemical ranges for personal and industrial HCN instruments.
Choose the HCN sensor around the hazard and instrument format
HCN is usually measured with amperometric electrochemical cells. The most important selection differences are mechanical format, T90, bias, humidity behavior, cross-sensitivity and whether the sensor will see gas only during incidents or continuously.
0–50 ppm
Miniature cells prioritize fast alarms and small package height for clip-on instruments.
- HCN-D4 / H4 class
- Fire, mining and rescue wearables
0–100 ppm
Standard A-Series or 20 mm cells fit handheld toxic-gas analyzers and multi-gas platforms.
- Petrochemical and chemical plants
- Confined-space checking
0–100 ppm
Larger electrolyte volume and environmental stability can help in humid or outdoor fixed installations.
- High-humidity plant areas
- Continuous fixed transmitters
0–50 / 100 ppm
Fast HCN should be combined with other fire gases rather than treated as a stand-alone combustion indicator.
- HCN + CO
- Fireground / overhaul
0–100 ppm
HCN can be associated with cyanide chemistry and acidic conditions; gas matrix and H₂S interference need explicit testing.
- Fixed or portable safety
- Headspace / local release monitoring
Gas-phase HCN
Use a gas sensor only when the target is HCN in air or headspace. Total cyanide in water is a different analytical task.
- Short gas path
- High humidity / condensation control
HCN cells are not electrically interchangeable
Hydrogen cyanide sensors use electrochemical reactions at a working electrode to produce a current related to HCN concentration. The mechanical principle is familiar, but the required electrode potential and analog front end can vary between products.
Working electrode
HCN reacts at the sensing electrode and produces the concentration-related current.
Sensitivity is specified in nA/ppm or µA/ppm.Reference electrode
Controls working-electrode potential and makes the specified bias condition possible.
Bias must follow the exact datasheet.Gas diffusion path
Membrane, cap and enclosure geometry determine how quickly HCN reaches the catalyst.
Finished T90 is usually slower than bare-cell T90.AFE / potentiostat
Converts low sensor current into a stable voltage or digital concentration.
Zero drift and bias stability affect low-ppm alarms.HCN sensors for wearable, portable and fixed safety systems
The most useful comparison is not simply 50 ppm versus 100 ppm. Package size, T90, bias, environmental behavior and interference profile often determine which HCN cell fits the instrument.
| OEM need | Manufacturer | Model | Type | Published range | Key engineering point | Official source |
|---|---|---|---|---|---|---|
| 20 mm industrial HCN | Winsen | ME3-HCN | 3-electrode EC | 0–100 ppm max 150 ppm | 0.2 ppm resolution, T90 <120 s, +300 mV bias and 2-year anticipated life. | Official ↗ |
| Miniature wearable | Alphasense | HCN-D4 | Miniature EC | 0–50 ppm | T90 <50 s, D-Series footprint and 30–50 nA/ppm sensitivity for clip-on personal monitors. | Official ↗ |
| Miniature wearable alternative | Alphasense | HCN-H4 | Miniature EC | 0–50 ppm | T90 <50 s, H-Series format for compact firefighting, mining and industrial wearables. | Official ↗ |
| Portable / general safety | Alphasense | HCN-A1 | A-Series EC | 0–100 ppm | T90 <70 s, 45–85 nA/ppm sensitivity and application positioning for firefighting, mining and industrial safety. | Official ↗ |
| Fixed / high-humidity | Alphasense | HCN-B1 | B-Series EC | 0–100 ppm | T90 <120 s, larger electrolyte volume and fixed/high-humidity positioning. | Official ↗ |
| Life-safety 7-Series route | Honeywell City Technology | 7HCN | 3-electrode EC | 0–100 ppm | 0.5 ppm resolution, T90 <200 s, no bias required and 2-year expected life in air. | Datasheet ↗ |
| Fast compact HCN | Membrapor | HCN/C-100 | 3-electrode EC | 0–100 ppm max 200 ppm | <0.3 ppm resolution, T90 <20 s, no bias recommended and 3–5 year application-based life. | Datasheet ↗ |
Published values are component specifications. Validate HCN response, interferents, bias, temperature and complete detector performance before production.
HCN sensor priorities change with the exposure scenario
Wearable and portable personal safety
Personal instruments need fast response in a small package, but the alarm channel also has to remain stable near a few ppm.
| Product | Range | T90 | Engineering point |
|---|---|---|---|
| Alphasense HCN-D4 | 0–50 ppm | <50 s | Miniature D-Series for slim clip-on instruments. |
| Alphasense HCN-H4 | 0–50 ppm | <50 s | Miniature H-Series route for wearable multi-gas platforms. |
| Membrapor HCN/C-100 | 0–100 ppm | <20 s | Very fast compact cell where 100 ppm full-scale coverage is preferred. |
Fixed industrial and high-humidity monitoring
Fixed transmitters often trade package size for electrolyte volume, environmental stability and longer service intervals.
| Route | Range | Strength | Watch point |
|---|---|---|---|
| Alphasense HCN-B1 | 0–100 ppm | B-Series fixed / high-humidity positioning. | Confirm interferents and response through the final enclosure. |
| Winsen ME3-HCN | 0–100 ppm | Compact 20 mm industrial raw cell. | Requires +300 mV bias and ≥48 h aging/stabilization before use per manual. |
| Honeywell 7HCN | 0–100 ppm | No-bias life-safety architecture. | Not recommended for repeated or continuous HCN exposure. |
Fire and emergency response
HCN is one of several toxic combustion products that can matter in fireground and post-fire environments. Portable multi-gas instruments should treat HCN as a dedicated channel rather than infer it from CO.
| Measurement need | Recommended design approach | Reason |
|---|---|---|
| Firefighter wearable | Miniature 0–50 ppm HCN + CO + O₂ / other required gases | Combines HCN alarm coverage with other immediately relevant fire hazards. |
| Post-fire overhaul | Portable pump or diffusion multi-gas instrument | Checks local pockets before respiratory protection is relaxed. |
| Hot smoke / remote sampling | Condition and validate the sample before the HCN cell | Electrochemical cell limits are not the same as raw smoke temperature and particulate conditions. |
HCN and CO should be measured as separate fire-gas channels
Combustion of nitrogen-containing materials can generate hydrogen cyanide. CO is also common in fires, but the concentrations do not follow a fixed ratio, so one gas should not be used as a universal surrogate for the other.
Portable / wearable design
- Use a dedicated HCN electrochemical cell.
- Combine with CO and the other gases required by the mission.
- Prioritize response time and low-ppm alarm stability.
- Check bump response before use according to the instrument procedure.
Smoke-laden sampling
- Protect the cell from soot and liquid contamination.
- Do not expose the electrochemical sensor directly to temperatures outside its rating.
- Account for pump and tubing delay in remote sampling.
- Validate the complete gas path with HCN target gas.
H₂S can produce a very large false HCN reading
Cross-sensitivity is one of the most important HCN selection factors. The direction and magnitude vary by chemistry, so use the exact sensor's interference table rather than a generic HCN correction.
| HCN sensor | Interfering gas | Test concentration | Published HCN-equivalent response | Engineering implication |
|---|---|---|---|---|
| Winsen ME3-HCN | H₂S | 20 ppm | 100 ppm | Strong positive false HCN response; mixed H₂S/HCN sites need a different strategy or validated compensation. |
| Winsen ME3-HCN | CO | 300 ppm | 20 ppm | Relevant in fire and combustion environments. |
| Winsen ME3-HCN | C₂H₄ | 100 ppm | 30 ppm | Review hydrocarbon/process gas composition. |
| Winsen ME3-HCN | SO₂ | 5 ppm | <8 ppm | Sulfur-gas mixtures can create material error at low HCN alarm levels. |
| Membrapor HCN/C-100 | H₂S | 15 ppm | ~25 ppm | Positive HCN bias even at modest H₂S concentration. |
| Membrapor HCN/C-100 | SO₂ | 20 ppm | ~38 ppm | Large positive response; evaluate sulfur processes carefully. |
| Membrapor HCN/C-100 | NO₂ | 5 ppm | ~−12 ppm | Negative interference can suppress a real HCN reading. |
Bias voltage changes the HCN electronics design
HCN cells from different manufacturers can use different electrode potentials. The analog front end must keep the working/reference relationship at the specified voltage during operation and, where required, during storage or startup.
Winsen ME3-HCN
- Published bias: +300 mV.
- Recommended load resistance: 10 Ω.
- Manual calls for at least 48 hours aging before use.
- PCB firmware should allow stabilization before trusting alarms.
Honeywell 7HCN / Membrapor HCN/C-100
- Honeywell 7HCN: bias not required.
- Membrapor HCN/C-100: bias not recommended.
- The AFE can therefore differ materially from a +300 mV design.
- Do not treat common range and pin count as electrical compatibility.
HCN life-safety cells may not tolerate continuous target gas
Published operating life is not the same as allowable cumulative HCN exposure. A sensor can age normally in clean air yet drift quickly when used as a continuous process monitor.
Occasional safety exposure
This is the intended duty for many personal and fixed life-safety HCN cells.
- Gas appears mainly during a leak, fire or test.
- Periodic bump and calibration checks confirm recovery.
Repeated release events
Repeated target-gas doses can change output and shorten replacement intervals.
- Track exposure history where possible.
- Recheck response after a significant HCN event.
Continuous process HCN
Use a sensor or analyzer specifically validated for continuous exposure.
- Honeywell 7HCN explicitly warns against repeated or continuous exposure.
- Do not extend a life-in-air claim to a constant HCN process stream.
HCN gas sensors do not measure total cyanide in water
Mining, electroplating and wastewater projects can involve both gaseous hydrogen cyanide and dissolved cyanide chemistry. The measurement method depends on which phase and chemical form the project needs to quantify.
| Measurement | Target | Typical unit | Instrument route | Example use |
|---|---|---|---|---|
| HCN gas | Hydrogen cyanide in air / headspace | ppm | Electrochemical gas sensor or detector | Worker safety, process release, tank / wastewater headspace |
| Cyanide in water | Dissolved / free / total cyanide depending method | mg/L | Water-analysis method or dedicated liquid analyzer | Mining water, plating wastewater, process chemistry |
Validate HCN through the complete enclosure or pumped sample path
Humidity, condensation, particles and sample-line delay can make a detector respond differently from the bare sensor. This becomes especially important in fire, wastewater headspace and pumped portable instruments.
Choose the point
Sample the breathing zone, process release point or representative headspace.
Control particles
Protect the diffusion barrier without excessively slowing HCN transport.
Avoid condensation
Keep liquid water away from the sensing inlet and sample line.
Measure transport delay
Pumps, tubing and filters add response time beyond the cell T90.
Test with HCN
Verify the assembled instrument with target gas at the final inlet.
ME3-HCN engineering profile
Winsen's current HCN gas-sensor listing centers on ME3-HCN, a 20 mm-class raw electrochemical cell for industrial and environmental HCN detection.
| Parameter | ME3-HCN published value | Design implication |
|---|---|---|
| Measurement range | 0–100 ppm | Suitable for general personal / industrial HCN range architecture. |
| Maximum detecting concentration | 150 ppm | Do not interpret max concentration as the normal calibrated measuring range. |
| Sensitivity | 0.1 ± 0.02 µA/ppm | AFE gain must support low-ppm resolution without saturation. |
| Resolution | 0.2 ppm | Useful for low-ppm industrial safety when complete-system noise is controlled. |
| T90 | <120 s | Finished detector response will also include enclosure / sample transport. |
| Bias voltage | +300 mV | Requires the correct potentiostat / bias architecture. |
| Anticipated life | 2 years | Life depends on storage, environment and exposure history. |
| Key published interference | 20 ppm H₂S → 100 ppm HCN equivalent | Do not use the cell in an H₂S-rich application without a validated mitigation strategy. |
Other hydrogen cyanide sensor product ranges
These manufacturers publish HCN sensors for personal monitors, fixed systems, fire and rescue, mining and industrial safety.
Alphasense
A-, B-, D- and H-Series HCN cells plus IST versions for wearable, portable and fixed instruments.
Honeywell City Technology
7HCN 0–100 ppm life-safety electrochemical sensor with no bias requirement.
Membrapor
HCN/C-100 compact electrochemical sensor with fast response and published cross-sensitivity data.
Submit an HCN sensor
Manufacturers can provide an official product page and current datasheet for inclusion.
HCN calibration should use target gas, not an interferent
Because cross-sensitivity varies so much between HCN cell chemistries, calibration with CO, H₂S or another surrogate gas can create large error. Use the instrument's approved HCN calibration method.
Bias stabilization
Allow the required bias / aging time before zeroing or calibration. This is especially important after power loss or sensor replacement.
Bump check
Confirms that HCN reaches the sensor and the measurement / alarm chain responds. Follow the finished detector procedure.
Post-exposure check
After a high HCN event or repeated gas exposure, confirm zero, span and response before returning the instrument to normal safety service.
Hydrogen cyanide sensor questions
What HCN sensor range is common for personal and industrial safety?
Many personal and industrial HCN electrochemical sensors use 0–50 ppm or 0–100 ppm measurement ranges. The useful range should preserve low-ppm alarm performance while covering the credible release concentration for the application.
Why is low-ppm performance important for HCN?
Hydrogen cyanide is highly toxic. NIOSH lists a 4.7 ppm short-term recommended exposure limit and a 50 ppm IDLH value. These are exposure references, not universal detector setpoints, but they show why resolution and response near the low-ppm region matter.
Why is H₂S cross-sensitivity a major issue for HCN sensors?
Some HCN electrochemical cells respond very strongly to hydrogen sulfide. For example, manufacturer data for several commercial HCN sensors show large positive H2S responses. A sensor that works in a clean HCN test can therefore over-read badly in mixed sulfur-gas environments.
Do all HCN electrochemical sensors require the same bias voltage?
No. Winsen ME3-HCN specifies a +300 mV bias, while Honeywell 7HCN specifies no bias. The analog front end must follow the exact cell datasheet; HCN sensors should not be treated as electrically interchangeable.
Why is HCN monitored in firefighting and post-fire overhaul?
Combustion of nitrogen-containing materials can produce hydrogen cyanide. Portable multi-gas instruments can monitor HCN together with CO and other hazards during fireground assessment, overhaul and confined-space checking.
Can an HCN sensor be used continuously in a process stream?
Only if the sensor is designed and validated for that exposure profile. Some life-safety HCN cells are intended for occasional gas exposure and can drift or age rapidly under repeated or continuous HCN exposure.
Does an HCN gas sensor measure cyanide in wastewater?
No. An HCN gas sensor measures gaseous hydrogen cyanide in air or headspace. Dissolved or total cyanide in water requires an appropriate water-analysis method or liquid-phase instrument.
How should HCN sensors be calibrated?
Use certified HCN calibration gas and the complete detector gas path. Follow the sensor or instrument instructions for bias stabilization, flow rate, temperature and bump testing, and use target gas rather than an interfering gas as a calibration surrogate.
Final checks before design freeze
Validate the finished HCN detector in the gas mixture and duty cycle expected in service. Low-ppm response, cross-sensitivity and cumulative target-gas exposure can matter more than nominal full scale.
- Confirm 0–50 ppm versus 0–100 ppm range around the actual safety task.
- Review H₂S, SO₂, CO, ethylene and oxidant cross-sensitivities for the exact cell.
- Match the AFE to the specified HCN bias voltage and sensor polarity.
- Add enclosure, filter, pump and tubing delay to the bare-sensor T90.
- Do not extend a life-in-air claim to repeated or continuous HCN exposure without validation.
- Use a dedicated HCN channel in fire / rescue instruments rather than infer HCN from CO.
- Separate gaseous HCN monitoring from liquid cyanide analysis.
Need an HCN sensor for an OEM project?
Send the target range, personal / fixed / fire / process application, expected interferents, humidity, response requirement, bias / interface constraints and exposure duty cycle. Manufacturers can also submit HCN sensor models with an official product page and current datasheet.
Specifications and product availability can change. Confirm the latest manufacturer datasheet before engineering, compliance or purchasing decisions.