Chloroform (CHCl₃)
Chloroform is a chlorinated solvent and chemical intermediate used in laboratories, pharmaceutical production and specialty processing. It can depress the central nervous system and affect the liver, kidneys and heart. Because its ionization potential is above the energy of a common 10.6 eV PID lamp, many general VOC instruments are unsuitable for reliable chloroform measurement without a different detection principle.
What Is Chloroform?
Chloroform is a chlorinated solvent and chemical intermediate used in laboratories, pharmaceutical production and specialty processing. It can depress the central nervous system and affect the liver, kidneys and heart. Because its ionization potential is above the energy of a common 10.6 eV PID lamp, many general VOC instruments are unsuitable for reliable chloroform measurement without a different detection principle.
Core references used for this page: NIOSH Pocket Guide — Chloroform; NIST Chemistry WebBook — Chloroform; NIOSH Pocket Guide to Chemical Hazards.
Chloroform at a Glance
Appearance and fire behavior
Colorless volatile liquid with a characteristic sweet odor
NIOSH lists chloroform as a noncombustible liquid. Heating or fire can generate highly toxic decomposition products, including phosgene and hydrogen chloride.
Exposure-limit context
NIOSH REL: carcinogen notation with a 2 ppm short-term limit over 60 minutes. OSHA PEL: 50 ppm ceiling. NIOSH IDLH: 500 ppm with carcinogen notation. These values are occupational references, not universal alarm settings.
Properties That Affect Safety and Measurement
| Property | Value or description | Engineering significance |
|---|---|---|
| Formula | CHCl3 | Identifies the target gas or atmospheric parameter. |
| CAS number | 67-66-3 | Useful for chemical records, SDS review and analytical methods. |
| Molecular weight | 119.38 g/mol | Supports engineering calculations but is not a complete detector-placement rule. |
| Boiling / phase behavior | About 61.2°C (142.2°F) | Important for cryogenic releases, frostbite and pressure control. |
| Relative gas density | Vapor about 4.1 times heavier than air | One dispersion input among release momentum, temperature, ventilation and geometry. |
| Appearance and odor | Colorless volatile liquid with a characteristic sweet odor | Human senses cannot provide a quantified or automatic safety response. |
| Fire behavior | NIOSH lists chloroform as a noncombustible liquid. Heating or fire can generate highly toxic decomposition products, including phosgene and hydrogen chloride. | Determines whether enrichment, oxidizing behavior or nonflammability must be addressed. |
| Exposure / threshold context | NIOSH REL: carcinogen notation with a 2 ppm short-term limit over 60 minutes. OSHA PEL: 50 ppm ceiling. NIOSH IDLH: 500 ppm with carcinogen notation. These values are occupational references, not universal alarm settings. | Do not treat occupational limits, oxygen boundaries and alarm settings as interchangeable. |
Gas density alone is not sufficient to determine detector placement. Release point, gas temperature, process pressure, ventilation, air movement, room geometry, obstructions and worker location must all be considered.
Where Chloroform Is Used or Released
Common sources and release points
- Laboratory extraction, synthesis and sample preparation
- Pharmaceutical and chemical manufacturing
- Refrigerant and fluorochemical feedstock operations
- Historical solvent use and contaminated waste streams
- Water-treatment by-product investigations and environmental sampling
- Spills, open vessels, transfer operations and heated processes
Industries and applications
Applications determine whether the measurement objective is personnel protection, process control, purity, emissions management or leak location.
- Chemical and pharmaceutical synthesis
- Laboratory extraction and analytical work
- Fluorochemical feedstock production
- Environmental and water-quality investigations
- Waste characterization and remediation
- Specialty process solvent use
Chemical and pharmaceutical synthesis
Review storage, transfer, process equipment, ventilation, occupied access and maintenance states for credible releases.
Laboratory extraction and analytical work
Review storage, transfer, process equipment, ventilation, occupied access and maintenance states for credible releases.
Fluorochemical feedstock production
Review storage, transfer, process equipment, ventilation, occupied access and maintenance states for credible releases.
Environmental and water-quality investigations
Review storage, transfer, process equipment, ventilation, occupied access and maintenance states for credible releases.
Waste characterization and remediation
Review storage, transfer, process equipment, ventilation, occupied access and maintenance states for credible releases.
Specialty process solvent use
Review storage, transfer, process equipment, ventilation, occupied access and maintenance states for credible releases.
Understand How Vapor Exposure Develops
Evaporation and vapor pressure
Chloroform can enter air from open containers, wet surfaces, spills, heated processes, coatings, cleaning and transfer operations. Temperature and exposed surface area can strongly change the release rate.
Inhalation and absorption
Chloroform is readily inhaled as vapor and can depress the central nervous system. Repeated or high exposure can injure the liver and kidneys; heated chloroform can form phosgene.
Fire or decomposition behavior
NIOSH lists chloroform as a noncombustible liquid. Heating or fire can generate highly toxic decomposition products, including phosgene and hydrogen chloride. A separate %LEL channel may be needed where fire protection is the objective.
Mixture and measurement uncertainty
Workplace air often contains several VOCs. A broad-response instrument may show a signal without identifying the compound or proving the concentration of this specific vapor.
Primary Hazards of Chloroform
People and atmosphere
- Central-nervous-system depression, dizziness and loss of coordination
- Liver and kidney injury after significant or repeated exposure
- Cardiac sensitization and potentially dangerous rhythm effects at high concentration
- Eye and skin irritation with liquid contact
- Potential occupational carcinogenicity
- Dense vapor may accumulate in poorly ventilated low areas
Reactivity, materials and equipment
- Keep away from strong caustics, strong oxidizers and chemically active metals.
- Heating or fire can form phosgene, hydrogen chloride and other hazardous products.
- Use seals, tubing and PPE materials verified for chlorinated-solvent service.
- Avoid relying on standard organic-vapor instruments unless the response to chloroform is specifically demonstrated.
Never enter an unknown atmosphere. Leave the affected area, contact trained emergency responders, use appropriate respiratory protection and follow the facility emergency plan.
Separate Exposure Limits, Alarm Settings and Instrument Ranges
NIOSH REL: carcinogen notation with a 2 ppm short-term limit over 60 minutes. OSHA PEL: 50 ppm ceiling. NIOSH IDLH: 500 ppm with carcinogen notation. These values are occupational references, not universal alarm settings.
Compound-specific ppm
Used for occupational exposure or process concentration. TWA, STEL, ceiling and IDLH values have different time bases and regulatory meanings.
TVOC / PID screening
A broad-response value can reveal change or locate a source, but it does not identify the compound and depends on lamp, correction factor and mixture.
Alarm programming
Alarm settings depend on the gas, application, jurisdiction, instrument, applicable standards and site-specific risk assessment.
Define the Safety Function Before Selecting a Sensor
Questions to answer
- What containers, coatings, cleaners, tanks or processes can release the vapor?
- Is the objective compound-specific exposure, TVOC screening, process analysis or %LEL protection?
- What ranges, response times and environmental limits apply?
- Which alarms control ventilation, isolation, evacuation or process action?
- How will the complete system be bump tested, calibrated and documented?
Instrument terms are not interchangeable
- Gas sensor: the sensing element.
- Gas detector: sensor plus electronics, output and alarm functions.
- Gas monitor: continuous or portable instrument that may log or calculate exposure.
- Gas analyzer: measures composition, purity or process concentration.
- Leak detector: locates or indicates leakage and may not report area concentration.
How Chloroform Vapor Is Measured
Photoionization detector (PID)
Ultraviolet photons ionize compounds whose ionization energy is below the lamp energy; the resulting current is related to vapor concentration.
Infrared / FTIR / photoacoustic
The instrument measures compound-specific infrared absorption in a cell or optical path.
Gas chromatography / laboratory analysis
A sample is separated into components before compound-specific detection and quantification.
Metal-oxide semiconductor (MOS)
A heated sensing surface changes resistance when exposed to reducing or oxidizing vapors.
Colorimetric or derivatization method
The vapor reacts with a treated medium or reagent to produce a measurable color or derivative.
Where Monitoring Points Should Be Installed
Priority locations
- Near credible chloroform release points such as tanks, pumps, valves, mixers, transfer connections and process enclosures
- At worker breathing zones or representative occupied locations when occupational exposure is the objective
- At low points, trenches, sumps or floor-level zones where dense vapor may accumulate, while still checking airflow and release temperature
- At local exhaust capture points, room returns and ventilation dead zones identified by airflow review
- At storage cabinets, coating or cleaning stations, laboratories and waste-handling areas where containers may be opened
- At confined-space entry points and inside the space under the approved atmospheric-testing plan
Placement review checklist
- Release point and failure mode
- Gas temperature, pressure and jet direction
- Normal, standby and failed ventilation states
- Room geometry, pits, ceilings and connected voids
- Worker breathing zones, exits and rescue approach
- Sampling delay and maintenance access
Validate detector coverage against real operating modes. A high or low mounting rule based only on molecular weight is not an adequate design method.
Prove the Complete Monitoring System Works
Functional verification
- Inspect power, enclosure, inlet, filter, wiring and fault status.
- Apply the correct challenge gas or reference atmosphere.
- Confirm response, display, local alarm, relays and remote notification.
- Calibrate when required or when the functional check fails.
- Record results, sensor age, faults and corrective action.
When additional testing is needed
- After over-range exposure or a high-concentration solvent release
- After condensation, washdown, filter loading or solvent contamination
- After repair, relocation, power loss or ventilation changes
- After unexplained drift, failed alarms or pump-flow faults
- Before critical confined-space or emergency work
Control Releases Before Relying on Alarms
Engineering controls
- Leak-tight piping, compatible materials and suitable pressure relief
- Ventilation sized for credible normal and abnormal releases
- Remote isolation, shutdown and safe discharge routing
- Alarm interlocks that are tested as a complete cause-and-effect system
- Confined-space, hazardous-location, hot-work and chemical-handling procedures as applicable
Gas-specific emergency priorities
- Leave the affected area and warn others; do not investigate an unknown atmosphere without suitable training and equipment.
- Eliminate ignition sources only when this can be done remotely or without entering the release area.
- Isolate the source and start engineered ventilation under the facility emergency plan.
- Use appropriate chemical-resistant PPE and atmosphere-supplying respiratory protection for emergency entry as required by the hazard assessment.
- Verify the specific vapor, oxygen and flammability conditions before re-entry or returning equipment to service.
Common Causes of Delayed or Misleading Readings
Sampling system considerations
- Use validated sorbent media and analytical methods for occupational measurements.
- Keep sample lines short and use materials compatible with chlorinated solvents.
- Avoid condensation and account for adsorption or desorption from tubing and filters.
- Confirm that broad VOC instruments can actually respond to chloroform before using them for screening.
Environmental and cross-sensitivity review
Verify PID lamp energy, response factors, background VOCs, oxygen dependency, pressure, temperature, humidity, condensation, response time, sensor aging and cross-sensitivity. The complete installed instrument—not only the bare sensor—must meet the required safety function.
Practical Answers to Frequent Mistakes
“Every PID detects chloroform.”
A common 10.6 eV PID may show little or no response because chloroform has a higher ionization potential.
“Nonflammable means harmless.”
Chloroform can still cause severe toxic effects and can form phosgene when heated.
“Odor gives an adequate warning.”
Odor is not a quantitative exposure method and may not protect every worker.
“A TVOC reading proves the chloroform concentration.”
A broad VOC signal does not identify chloroform or establish its specific concentration.
Comparing Measurement Approaches
| Technology | Suitable use | Advantages | Limitations |
|---|---|---|---|
| Photoionization detector (PID) | Only with a lamp whose photon energy exceeds chloroform’s ionization potential and with a validated response factor. | Fast response, broad VOC sensitivity and useful portable screening capability. | A common 10.6 eV PID generally will not ionize chloroform effectively; ordinary PID screening can therefore give a false sense of safety. |
| Infrared / FTIR / photoacoustic | Compound-specific fixed, portable or extractive monitoring where the optical method is designed for chloroform. | Can provide direct compound-specific measurement and is not dependent on oxygen for the optical response. | Water vapor and other chlorinated solvents can overlap spectrally; the measurement path and library must be validated. |
| Gas chromatography / laboratory analysis | Occupational hygiene, environmental confirmation and mixed-solvent identification. | High specificity and defensible identification in complex mixtures. | Sampling integrity, laboratory turnaround and instrument expertise are required. |
| Metal-oxide semiconductor (MOS) | Broad leak or trend screening where non-specific response is acceptable. | Compact, economical and sensitive to many VOCs. | Poor selectivity and strong response to many other VOCs limit quantitative use. |
| Colorimetric or derivatization method | Short-term screening or validated sorbent-tube methods for specific tasks. | Compound-focused spot checks or validated sampling methods can reach low concentrations. | Tube chemistry, sampling volume, humidity and other chlorinated compounds can affect results. |
Chloroform FAQ
What does chloroform smell like?
Odor descriptions vary and odor thresholds do not equal safe exposure limits. Smell must not be used as the primary warning method for Chloroform.
Is chloroform a VOC?
Chloroform is commonly discussed as a volatile organic compound or solvent vapor because it can enter air readily under relevant use conditions.
Is chloroform flammable?
NIOSH lists chloroform as a noncombustible liquid. Heating or fire can generate highly toxic decomposition products, including phosgene and hydrogen chloride. Verify the current SDS and process conditions because temperature, pressure and mixture composition affect fire behavior.
Is chloroform heavier than air?
The typical vapor-density reference is Vapor about 4.1 times heavier than air. Density is only one input; release momentum, temperature, ventilation and room geometry determine actual movement.
Can a PID detect chloroform?
Fast response, broad VOC sensitivity and useful portable screening capability. A common 10.6 eV PID generally will not ionize chloroform effectively; ordinary PID screening can therefore give a false sense of safety.
Which sensor is best for chloroform?
The correct method depends on whether the goal is compound-specific exposure measurement, broad VOC screening, leak detection, process analysis or %LEL fire protection. No single sensor is best for every objective.
Where should chloroform detectors be installed?
Place instruments from the release scenario, airflow, worker location, vapor behavior and required response time. Gas density alone is not sufficient to determine detector placement.
What measuring range should be used for chloroform?
Select a range around the applicable exposure limit or process objective, expected background, credible release and required resolution. A %LEL range and a ppm exposure range serve different purposes.
How often should chloroform detectors be calibrated?
Follow the instrument manufacturer, site procedure, applicable regulation and risk assessment. Bump testing proves response; calibration adjusts accuracy and should also follow failed tests, over-range events or contamination.
What should be done during a chloroform leak?
Leave the affected area, prevent unprotected entry, contact trained emergency responders, isolate remotely if safe and follow the facility emergency plan.
Sources and Further Reading
Requirements and numerical values may differ by jurisdiction, standard, pressure, altitude, composition and test condition. Use the original sources and applicable local rules when designing a system.
- NIOSH Pocket Guide — Chloroform
- NIST Chemistry WebBook — Chloroform
- NIOSH Pocket Guide to Chemical Hazards
- OSHA 1910.1000 — Air Contaminants
- U.S. EPA — Volatile Organic Compounds and Indoor Air Quality
- PubChem — Chloroform
- OSHA 1910.134 — Respiratory Protection
Educational content only: This page does not replace emergency services, medical advice, a workplace risk assessment, applicable codes, manufacturer instructions or qualified engineering judgement.
Plan a Chloroform Vapor Monitoring System
Share the solvent or process source, target concentration, other VOCs, temperature, humidity, ventilation, required response time, certifications and maintenance constraints.