Bromine (Br₂)
Bromine is a dark reddish-brown, fuming liquid at room temperature that readily generates dense, corrosive and toxic vapor. It is a strong oxidizer used in chemical synthesis, water treatment and brominated-product manufacture, requiring low-ppm detection and strict material compatibility.
What Is Bromine?
Bromine (Br2) is encountered as dark reddish-brown fuming liquid with suffocating, irritating fumes. Common synonyms include Molecular bromine.
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.
Bromine 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 | Br2 | Confirms the target species and avoids confusion with related gases. |
| CAS number | 7726-95-6 | Useful for SDS, regulatory and calibration documentation. |
| Molecular weight | 159.8 g/mol | Supports comparison, but does not by itself predict detector height. |
| Physical description | Dark reddish-brown fuming liquid with suffocating, irritating fumes | Human senses are not a quantitative measuring method. |
| Boiling point | 139°F (about 59°C) | Indicates whether liquid flashing, condensation or cryogenic effects may occur. |
| Gas/vapor behavior | Dense vapor; molecular weight and liquid release support low spreading, but airflow remains decisive | Must be combined with temperature, momentum and ventilation. |
| Fire/oxidation behavior | Noncombustible, but accelerates burning as an oxidizer | Determines whether toxic, flammable and oxidizer controls must be layered. |
| Conversion | 1 ppm = 6.54 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 Bromine 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
Bromine storage, transfer and rail or cylinder handling
Source 2
Brominated flame-retardant and chemical-intermediate production
Source 3
Water treatment, cooling water and pool/spa bromination
Source 4
Pharmaceutical, dye and agrochemical synthesis
Source 5
Laboratory reactions and bromination systems
Source 6
Accidental mixing or decomposition of bromine-releasing products
Industries and applications
- Organic and inorganic bromination
- Water treatment and biocidal chemistry
- Flame-retardant and specialty-material production
- Pharmaceutical and agrochemical intermediates
Why Is Bromine 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
Severe eye, skin and respiratory irritation or burns
Health concern 2
Cough, chest pressure, pneumonitis and pulmonary edema
Health concern 3
Headache, dizziness and systemic effects after significant exposure
Health concern 4
Liquid contact causes chemical burns
Health concern 5
Delayed lung injury may occur after inhalation
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.
Bromine Exposure Limits
| Reference | Value | Time basis and scope |
|---|---|---|
| NIOSH REL | TWA 0.1 ppm; ST 0.3 ppm | U.S. recommended occupational exposure limit; see the cited NIOSH record. |
| OSHA PEL | TWA 0.1 ppm | U.S. federal occupational limit for covered workplaces; verify the applicable standard and state plan. |
| NIOSH IDLH | 3 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.
Bromine 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 Bromine
No single technology is best for every range, environment or maintenance program.
Electrochemical
Working principle: Bromine is reduced at an electrode and generates a current.
Suitable use: Low-ppm portable and fixed monitoring.
Advantages: Direct local response and compact design.
Limitations: Cross-sensitivity to chlorine and other oxidants; corrosive exposure can shorten life.
Colorimetric tape
Working principle: Bromine stains a treated tape and optical electronics quantify the change.
Suitable use: Low-level multipoint and specialty-process monitoring.
Advantages: Sensitive and provides event history.
Limitations: Consumables, tubing losses and oxidant interferences.
UV-visible optical
Working principle: The strong visible/UV absorption of bromine is measured through a cell or optical path.
Suitable use: Process concentration and controlled extractive systems.
Advantages: Potentially selective and nonconsumptive.
Limitations: Window fouling, condensation, pressure and calibration path length matter.
Colorimetric tube
Working principle: Bromine reacts with a reagent tube to create a stain.
Suitable use: Spot checks and task surveys.
Advantages: Simple and targeted.
Limitations: Manual, single-use and affected by other halogens.
| Technology | Best fit | Advantages | Key limitations |
|---|---|---|---|
| Electrochemical | Low-ppm portable and fixed monitoring. | Direct local response and compact design. | Cross-sensitivity to chlorine and other oxidants; corrosive exposure can shorten life. |
| Colorimetric tape | Low-level multipoint and specialty-process monitoring. | Sensitive and provides event history. | Consumables, tubing losses and oxidant interferences. |
| UV-visible optical | Process concentration and controlled extractive systems. | Potentially selective and nonconsumptive. | Window fouling, condensation, pressure and calibration path length matter. |
| Colorimetric tube | Spot checks and task surveys. | Simple and targeted. | Manual, single-use and affected by other halogens. |
Where Should Bromine Detectors Be Installed?
Detector placement should be documented against the actual release and ventilation path.
Candidate locations
- Near bromine tanks, pumps, loading connections and vapor return lines
- Low and intermediate locations where liquid spills can fume and spread
- At breathing zones and access doors
- Inside storage enclosures and process cabinets where service is safe
- Near scrubber and exhaust interfaces
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
- Bromine is reactive and may be lost on wet, dirty or incompatible surfaces
- Use short corrosion-resistant lines and avoid metal parts not rated for bromine
- Prevent condensation of liquid bromine in sample tubing
- Validate response with the entire installed sample system and representative humidity
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
Bromine Detection Myths
“Bromine is a gas stored in cylinders only.”
At room temperature bromine is normally a fuming liquid that releases hazardous vapor.
“Its dark color makes instruments unnecessary.”
Low hazardous concentrations may not be visually obvious, and poor lighting or mixed air obscures color.
“Nonflammable means it will not worsen a fire.”
Bromine is an oxidizer and can accelerate combustion or react violently with fuels.
“Chlorine and bromine sensors are interchangeable.”
Cross-response may occur, but calibration, filters and performance claims must be gas-specific.
Monitoring Method Comparison
| Monitoring approach | Typical range | Primary objective | Important distinction |
|---|---|---|---|
| Electrochemical Br₂ | Low ppm | Local safety | Compact; halogen cross-response |
| Colorimetric tape | Very low ppm | Multipoint process | Sensitive; consumables |
| UV-visible analyzer | Process range | Concentration control | Optical; path and fouling effects |
| Detector tube | Task range | Spot survey | Manual single-use |
Bromine FAQ
Concise answers to common project, safety and search questions.
Is bromine a gas or a liquid?
Bromine is a dark reddish-brown liquid at room temperature that produces hazardous fuming vapor.
What does bromine smell like?
Its fumes are suffocating and irritating, but odor cannot be used to determine concentration.
Is bromine flammable?
No. It is noncombustible, but it is a strong oxidizer that can accelerate burning.
Is bromine vapor heavier than air?
Bromine vapor is dense, but ventilation, spill temperature and obstacles still determine the real cloud path.
What sensor detects bromine?
Electrochemical sensors and colorimetric tape systems are common for low-ppm safety; optical analyzers can support process measurement.
Can a chlorine sensor detect bromine?
Some sensors cross-respond, but that does not prove accurate bromine measurement. Use gas-specific performance data and calibration.
Where should bromine detectors be installed?
Near storage, transfer and spill sources, plus breathing zones and egress, using airflow analysis.
Why are bromine sample lines difficult?
Bromine is reactive, corrosive and condensable, so unsuitable or long lines can delay response.
How often should bromine detectors be calibrated?
Follow the manufacturer and site risk program, with compatible materials and suitable bromine challenge methods.
What should be done during a bromine release?
Evacuate, avoid contact and unknown atmospheres, and contact trained hazmat responders under the facility 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 — Bromine
NIOSH IDLH — Bromine
NIST Chemistry WebBook — Bromine
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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