Arsine (AsH₃)
Arsine is an extremely toxic, flammable gas used in semiconductor processing and capable of forming unintentionally when arsenic compounds contact newly generated hydrogen. Its hallmark systemic hazard is destruction of red blood cells, which can lead to hemoglobin in urine, jaundice and acute kidney injury after exposure.
What Is Arsine?
Arsine (AsH3) is encountered as colorless gas with a mild garlic-like odor that is not a reliable warning. Common synonyms include Arsenic hydride, arsenic trihydride, hydrogen arsenide.
Alarm settings depend on the gas, application, jurisdiction, instrument, applicable standards and site-specific risk assessment. Occupational limits, IDLH values, instrument ranges and alarm setpoints are related but are not interchangeable.
Arsine Key Properties
The values below support preliminary hazard review and instrument selection. Confirm current standards, the safety data sheet, process conditions and local legal requirements before design.
| Property | Value or description | Design relevance |
|---|---|---|
| Chemical formula | AsH3 | Confirms the target species and avoids confusion with related gases. |
| CAS number | 7784-42-1 | Useful for SDS, regulatory and calibration documentation. |
| Molecular weight | 78.0 g/mol | Supports comparison, but does not by itself predict detector height. |
| Physical description | Colorless gas with a mild garlic-like odor that is not a reliable warning | Human senses are not a quantitative measuring method. |
| Boiling point | −81°F (about −62°C) | Indicates whether liquid flashing, condensation or cryogenic effects may occur. |
| Gas/vapor behavior | About 2.69 relative to air | Must be combined with temperature, momentum and ventilation. |
| Fire/oxidation behavior | Flammable; NIOSH lists approximately 5.1–78% by volume | Determines whether toxic, flammable and oxidizer controls must be layered. |
| Conversion | 1 ppm = 3.19 mg/m³ | Supports comparison of ppm and mg/m³ references. |
Gas density alone is not sufficient to determine detector placement. Release point, gas temperature, process pressure, ventilation, air movement, room geometry, obstructions, pits, worker breathing zones and sample-line design must also be considered.
Where Does Arsine Come From?
The gas can be intentionally used, formed as a process intermediate, released from stored material or generated by an unintended reaction.
Source 1
Semiconductor arsine cylinders, gas cabinets and epitaxy/implant tools
Source 2
Acid cleaning of arsenic-contaminated metal
Source 3
Arsenic compounds contacting nascent hydrogen from metal-acid reactions
Source 4
Smelting, refining and metallurgical maintenance
Source 5
Battery, plating and laboratory reactions involving arsenic
Source 6
Accidental generation in wastewater or chemical treatment systems
Industries and applications
- Semiconductor doping and epitaxy
- Specialty chemical and research processes
- Calibration gas mixtures under strict controls
- Historical metallurgy and analytical chemistry contexts
Why Is Arsine Dangerous?
Health effects depend on concentration, duration, breathing rate, route of exposure and individual susceptibility. A suspected significant exposure requires professional medical evaluation.
Health concern 1
Rapid intravascular hemolysis destroys red blood cells
Health concern 2
Headache, weakness, dizziness, nausea and abdominal or back pain
Health concern 3
Dark or bloody urine, jaundice and kidney injury may develop after exposure
Health concern 4
Severe cases can cause anemia, shock and death
Health concern 5
Symptoms may be delayed, so medical observation and laboratory testing are critical
Do not use this page for medical diagnosis. Move exposed people to fresh air only without endangering rescuers, contact emergency services and tell medical staff the suspected gas and exposure circumstances.
Arsine Exposure Limits
| Reference | Value | Time basis and scope |
|---|---|---|
| NIOSH REL | Carcinogen; ceiling 0.002 mg/m³ for 15 minutes | U.S. recommended occupational exposure limit; see the cited NIOSH record. |
| OSHA PEL | TWA 0.05 ppm (0.2 mg/m³) | U.S. federal occupational limit for covered workplaces; verify the applicable standard and state plan. |
| NIOSH IDLH | Carcinogen notation; 3 ppm value shown by NIOSH | Emergency respirator-selection reference; not a routine alarm target or safe exposure level. |
| Instrument alarm | Site-specific | Set through applicable standards, risk assessment, response time and instrument performance. |
Keep units and objectives separate: ppm toxic exposure monitoring, %LEL flammable-gas monitoring and vol% process or asphyxiation measurement are different tasks.
Arsine Detection Strategy
Start with the safety objective, not the sensor catalog. Define the release and response before choosing technology.
Define the measurement
- Identify the target gas and credible interfering gases.
- Set the required range, resolution and response time.
- Decide whether the reading protects a person, room, process or property boundary.
- Specify environmental and certification requirements.
- Define alarm actions, data logging and proof testing.
Distinguish the equipment
- Gas sensor: the sensing element or module.
- Gas detector: a complete alarm/transmitter around a sensor.
- Gas monitor: an instrument that displays, logs or calculates exposure.
- Gas analyzer: a measurement system for higher accuracy, speciation or process control.
- Leak detector: equipment optimized to locate or warn about releases.
Sensor and Analyzer Technologies for Arsine
No single technology is best for every range, environment or maintenance program.
Electrochemical
Working principle: AsH₃ is oxidized at a specialized electrode, producing a current.
Suitable use: Fixed and portable low-ppb/ppm safety monitoring where specified.
Advantages: Compact and fast local alarm.
Limitations: Very low required levels, cross-sensitivity and high-dose recovery demand gas-specific qualification.
Colorimetric tape
Working principle: Arsine stains chemically treated tape, read optically.
Suitable use: Semiconductor multipoint monitoring.
Advantages: High sensitivity and permanent event record.
Limitations: Consumables, sample delay and interferences from other hydrides.
Atomic absorption / ICP methods
Working principle: Arsenic is collected or converted and measured elementally.
Suitable use: Industrial hygiene confirmation and laboratory analysis.
Advantages: Very sensitive and specific for arsenic.
Limitations: Not a real-time area alarm and may not distinguish species without method design.
FTIR / laser spectroscopy
Working principle: Optical absorption is measured for arsine.
Suitable use: Specialized process and high-purity gas analysis.
Advantages: Potentially selective and nonconsumptive.
Limitations: High cost, optical-path requirements and ultra-low detection challenges.
| Technology | Best fit | Advantages | Key limitations |
|---|---|---|---|
| Electrochemical | Fixed and portable low-ppb/ppm safety monitoring where specified. | Compact and fast local alarm. | Very low required levels, cross-sensitivity and high-dose recovery demand gas-specific qualification. |
| Colorimetric tape | Semiconductor multipoint monitoring. | High sensitivity and permanent event record. | Consumables, sample delay and interferences from other hydrides. |
| Atomic absorption / ICP methods | Industrial hygiene confirmation and laboratory analysis. | Very sensitive and specific for arsenic. | Not a real-time area alarm and may not distinguish species without method design. |
| FTIR / laser spectroscopy | Specialized process and high-purity gas analysis. | Potentially selective and nonconsumptive. | High cost, optical-path requirements and ultra-low detection challenges. |
Where Should Arsine Detectors Be Installed?
Detector placement should be documented against the actual release and ventilation path.
Candidate locations
- Inside gas cabinets, valve manifold boxes and exhausted enclosures
- Near semiconductor tool connections and abatement interfaces
- At breathing zones and access points outside containment
- Near acid cleaning or maintenance tasks on arsenic-contaminated equipment
- At low levels where dense gas can spread, while also accounting for cabinet exhaust and room mixing
Placement review checklist
- Release point and source elevation
- Gas or aerosol temperature and process pressure
- Normal and emergency ventilation
- Airflow direction, doors, ducts and obstructions
- Pits, trenches, cabinets and equipment enclosures
- Worker breathing zones and egress routes
- Maintenance access and calibration-gas connection
- Sampling-line delay and failure modes
Gas density alone is not sufficient to determine detector placement. Confirm proposed locations with drawings, smoke testing, ventilation data, dispersion analysis or representative release tests as appropriate.
Calibration, Bump Testing and Maintenance
A detector is reliable only when the complete sensing and alarm chain is maintained.
Bump test
Expose the instrument to a known gas to confirm gas reaches the sensor and the display and alarms respond. A bump test is not a full calibration.
Calibration
Apply traceable gas or a manufacturer-approved generator at the correct concentration, regulator, tubing, flow and environmental conditions.
System proof test
Verify relays, ventilation, shutdowns, beacons, remote annunciation, data logging, sample pumps and line-fault detection.
Frequency is not universal. Follow the manufacturer, certification, site procedure and risk assessment. Increase checks after high exposure, poisoning, water ingress, repair, prolonged storage or abnormal readings.
Engineering Controls and Emergency Response
Use a hierarchy: reduce inventory, contain the process, ventilate or scrub releases, detect early, automate safe actions where appropriate and prepare people for evacuation and trained response.
Engineering and administrative controls
- Closed transfer and suitable secondary containment
- Local exhaust, room ventilation and treatment or scrubbing
- Isolation valves, excess-flow protection and emergency shutdown
- Mechanical integrity, inspection and preventive maintenance
- Restricted access, signage, training and written procedures
- Emergency communication, drills and medical planning
During a suspected release
- Leave the affected area and move crosswind or upwind as directed.
- Do not enter or re-enter an unknown atmosphere.
- Contact trained emergency responders and identify the gas if known.
- Use appropriate respiratory protection only within a formal response program.
- Follow the facility emergency plan and seek medical evaluation after exposure.
Unknown or IDLH atmospheres require positive-pressure SCBA or an equivalent approved supplied-air configuration used by trained responders. Cartridge respirators are not appropriate for uncontrolled rescue entry.
Sampling, Materials and Cross-Sensitivity
Remote and extractive systems can fail even when the sensing element is healthy. Gas transport, line material and conditioning must be treated as part of the measurement.
Gas-specific challenges
- Use short inert sample lines; hydride losses and delay must be characterized
- Multipoint systems require documented transport time to every location
- Cross-contamination between sample points can be significant at ultra-low levels
- Validate the complete line using a safe certified arsine challenge method
Commissioning checks
- Measure transport time from every point
- Challenge the full installed line and filters
- Test realistic humidity and temperature
- Verify flow-fault and blocked-line alarms
- Document purge time after high exposure
- Prevent cross-contamination between points
Arsine Detection Myths
“Garlic odor gives sufficient warning.”
The odor is mild, variable and far above levels of concern; instrumentation is essential.
“Arsine exposure only irritates the lungs.”
Its major systemic effect is hemolysis, followed by kidney and liver injury.
“Arsine occurs only in semiconductor plants.”
It can be generated unintentionally when arsenic contamination contacts nascent hydrogen.
“A general toxic-gas sensor can be assumed to meet arsine limits.”
Required sensitivity and selectivity are demanding and must be explicitly qualified.
Monitoring Method Comparison
| Monitoring approach | Typical range | Primary objective | Important distinction |
|---|---|---|---|
| Electrochemical AsH₃ | Very low ppm | Local safety | Fast; gas-specific qualification |
| Colorimetric tape | ppb to low ppm | Semiconductor multipoint | Sensitive; consumables |
| Laboratory arsenic method | Trace mass | Exposure confirmation | Not continuous |
| Optical analyzer | Process-specific | High-purity/process | Specialized and costly |
Arsine FAQ
Concise answers to common project, safety and search questions.
What does arsine smell like?
Arsine may have a mild garlic-like odor, but it is not a reliable warning at hazardous concentrations.
Is arsine flammable?
Yes. NIOSH lists a flammable range of about 5.1% to 78% by volume.
Is arsine heavier than air?
Its relative gas density is about 2.69, but exhausted cabinets and room ventilation can dominate movement.
What sensor detects arsine?
Specialized electrochemical sensors and colorimetric tape systems are common for semiconductor safety monitoring.
What is the main health effect of arsine?
Arsine destroys red blood cells, which can cause anemia, dark urine, jaundice and acute kidney injury.
How can arsine form accidentally?
Arsenic compounds or contaminated metal can generate arsine when exposed to newly formed hydrogen, such as during acid-metal reactions.
Where should arsine detectors be installed?
Inside exhausted gas enclosures, near tool connections and at occupied access points.
Why are arsine limits difficult for instruments?
The target levels are extremely low, so line losses, cross-sensitivity, zero stability and calibration quality are critical.
How often should arsine systems be tested?
Use the manufacturer and semiconductor facility program, including end-to-end tests of multipoint lines and alarm actions.
What should be done after possible arsine exposure?
Leave the area and obtain urgent medical evaluation even if symptoms are mild, because hemolysis and kidney injury may develop later.
Sources and Further Reading
These sources support the identity, physical-property, occupational-limit and emergency information used on this page. Verify the current edition and the rules that apply to the facility.
NIOSH Pocket Guide — Arsine
NIOSH IDLH — Arsine
NIST Chemistry WebBook — Arsine
OSHA Annotated Table Z-1
Educational content only: This page does not replace an SDS, engineering analysis, occupational-hygiene assessment, emergency services, medical advice, applicable codes or the instrument manufacturer’s instructions.
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