Hydrogen Bromide (HBr)
Hydrogen bromide is a colorless, sharp-smelling and highly water-soluble acid gas. It is used in bromide chemistry and semiconductor processing and becomes hydrobromic acid in moisture, creating respiratory, corrosion and sample-line challenges similar to—but not identical with—hydrogen chloride.
What Is Hydrogen Bromide?
Hydrogen Bromide (HBr) is encountered as colorless gas with a sharp, irritating odor. Common synonyms include Anhydrous hydrogen bromide; hydrobromic acid in solution.
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.
Hydrogen Bromide 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 | HBr | Confirms the target species and avoids confusion with related gases. |
| CAS number | 10035-10-6 | Useful for SDS, regulatory and calibration documentation. |
| Molecular weight | 80.9 g/mol | Supports comparison, but does not by itself predict detector height. |
| Physical description | Colorless gas with a sharp, irritating odor | Human senses are not a quantitative measuring method. |
| Boiling point | −88°F (about −67°C) | Indicates whether liquid flashing, condensation or cryogenic effects may occur. |
| Gas/vapor behavior | About 2.81 relative to air | Must be combined with temperature, momentum and ventilation. |
| Fire/oxidation behavior | Nonflammable | Determines whether toxic, flammable and oxidizer controls must be layered. |
| Conversion | 1 ppm = 3.31 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 Hydrogen Bromide 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
Anhydrous HBr cylinders, manifolds and gas cabinets
Source 2
Hydrobromic acid storage and transfer
Source 3
Semiconductor etch, cleaning and process equipment
Source 4
Bromide and organic synthesis reactors
Source 5
Pharmaceutical and specialty-chemical production
Source 6
Thermal decomposition of brominated materials
Industries and applications
- Bromide and pharmaceutical synthesis
- Semiconductor etching and chamber processing
- Catalyst and specialty chemical manufacture
- Laboratory and analytical chemistry
Why Is Hydrogen Bromide 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
Eye, nose, throat and skin irritation
Health concern 2
Concentrated vapor can cause corrosive airway injury
Health concern 3
Solution contact causes severe chemical burns
Health concern 4
Liquefied HBr can cause frostbite
Health concern 5
Severe inhalation may lead to delayed lung injury
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.
Hydrogen Bromide Exposure Limits
| Reference | Value | Time basis and scope |
|---|---|---|
| NIOSH REL | Ceiling 3 ppm | U.S. recommended occupational exposure limit; see the cited NIOSH record. |
| OSHA PEL | TWA 3 ppm | U.S. federal occupational limit for covered workplaces; verify the applicable standard and state plan. |
| NIOSH IDLH | 30 ppm | 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.
Hydrogen Bromide 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 Hydrogen Bromide
No single technology is best for every range, environment or maintenance program.
Electrochemical
Working principle: HBr reacts at an acid-gas electrode and produces a current.
Suitable use: Portable and fixed low-ppm monitoring.
Advantages: Compact and practical for local leak warning.
Limitations: Cross-sensitivity to HCl and other acid gases; humidity and corrosive loading affect life.
Colorimetric tape
Working principle: A treated tape changes color when exposed to HBr.
Suitable use: Sensitive multipoint specialty-gas monitoring.
Advantages: Low detection levels and recorded stains.
Limitations: Consumables, sample delay and line adsorption.
FTIR
Working principle: Infrared absorption is measured for HBr.
Suitable use: Process, exhaust and extractive multipoint systems.
Advantages: Selective and capable of multi-gas measurement.
Limitations: HBr is adsorptive and corrosive; heated inert lines may be required.
Detector tube
Working principle: A reagent tube creates a visible stain after a defined sample volume.
Suitable use: Spot checks and task surveys.
Advantages: Simple and targeted.
Limitations: Manual, single-use and affected by related acid gases.
| Technology | Best fit | Advantages | Key limitations |
|---|---|---|---|
| Electrochemical | Portable and fixed low-ppm monitoring. | Compact and practical for local leak warning. | Cross-sensitivity to HCl and other acid gases; humidity and corrosive loading affect life. |
| Colorimetric tape | Sensitive multipoint specialty-gas monitoring. | Low detection levels and recorded stains. | Consumables, sample delay and line adsorption. |
| FTIR | Process, exhaust and extractive multipoint systems. | Selective and capable of multi-gas measurement. | HBr is adsorptive and corrosive; heated inert lines may be required. |
| Detector tube | Spot checks and task surveys. | Simple and targeted. | Manual, single-use and affected by related acid gases. |
Where Should Hydrogen Bromide Detectors Be Installed?
Detector placement should be documented against the actual release and ventilation path.
Candidate locations
- Near HBr gas cabinets, cylinder connections and valve manifold boxes
- Near acid tanks, pumps and transfer points
- At breathing zones and enclosure access points
- Near tool exhaust and scrubber interfaces
- At low points only where cool dense releases and ventilation support that location
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
- HBr is highly water soluble and adsorptive
- Use short inert, corrosion-resistant and dry sample lines
- Avoid wet filters and metal parts not approved for HBr
- Prove response through the installed line using the specified calibration 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
Hydrogen Bromide Detection Myths
“HBr and HCl use the same detector without qualification.”
Some sensors cross-respond, but accurate HBr performance requires gas-specific calibration and specifications.
“Hydrobromic acid vapor is only a skin hazard.”
Inhaled HBr can cause severe airway and lung injury.
“Dense gas means one floor-level detector is enough.”
Cabinet exhaust, hot process gas and air movement can move HBr away from the floor.
“A clean sensor calibration proves the remote system.”
Sample-line adsorption and moisture can dominate installed response.
Monitoring Method Comparison
| Monitoring approach | Typical range | Primary objective | Important distinction |
|---|---|---|---|
| Electrochemical HBr | Low ppm | Local safety | Compact; acid-gas cross-response |
| Colorimetric tape | Very low ppm | Multipoint semiconductor | Sensitive; consumables |
| FTIR | ppm and above | Process/exhaust | Multi-gas; heated sampling |
| Detector tube | Task range | Spot survey | Manual single-use |
Hydrogen Bromide FAQ
Concise answers to common project, safety and search questions.
What does hydrogen bromide smell like?
HBr has a sharp, irritating odor, but smell cannot determine concentration or prove that an area is safe.
Is hydrogen bromide flammable?
No. It is nonflammable, but it is highly corrosive and toxic by inhalation.
Is HBr heavier than air?
NIOSH lists a relative gas density of about 2.81, although release momentum and ventilation still control movement.
What sensor detects hydrogen bromide?
Electrochemical sensors, colorimetric tape systems and FTIR analyzers are used depending on range and application.
Does HBr form hydrobromic acid?
Yes. Hydrogen bromide dissolves readily in moisture to form hydrobromic acid.
Can an HCl sensor detect HBr?
It may respond, but that response may not be accurate or certified for HBr. Verify the manufacturer’s HBr data.
Where should HBr detectors be installed?
Near gas delivery and process leak points, breathing zones and exhaust pathways, based on airflow.
Why can remote HBr detection be slow?
HBr is adsorptive and water soluble, so long or wet sample lines can remove gas.
How often should HBr monitors be calibrated?
Follow the manufacturer and site risk program with corrosion-compatible equipment.
What should be done during an HBr release?
Evacuate, avoid unknown atmospheres and contact trained emergency responders under the site plan.
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 — Hydrogen Bromide
NIOSH IDLH — Hydrogen Bromide
NIST Chemistry WebBook — Hydrogen Bromide
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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