No metadata available
Chemical Identity
CAS Number
7446-09-5
Formula
SO₂
Molecular Weight
64.06 g/mol
Exposure Limits Comparison
Health Effects
Respiratory Irritation
Yes
Bronchospasm
Yes
Asthma Trigger
Yes
Pulmonary Edema
Yes
Alessandro MorettiPh.D.Italy
Laser-Based Additive ManufacturingPublished
Jan 6, 2026
Sulfur Dioxide Compound
Sulfur Dioxide Compound safety information for laser cleaning. Health hazards, exposure limits, and protective equipment requirements.
Chemical Properties
Detection Monitoring
- SensorTypes
- Electrochemical
- UV fluorescence
- Infrared
- DetectionRange
- 0-50 ppm typical
- AlarmSetpoints
- Low
- 2 ppm (NIOSH REL)
- High
- 5 ppm (OSHA PEL/NIOSH STEL)
- Evacuate
- 100 ppm (NIOSH IDLH)
- ColorimetricTubes
- Dräger SO2 0.1/a
- Gastec 5L
- Kitagawa 103
- AnalyticalMethods
Method Technique DetectionLimit NIOSH 6004 Ion chromatography 0.05 ppm OSHA ID-104 Ion chromatography 0.02 ppm - OdorThreshold
- 0.3-1 ppm - provides adequate warning below toxic levels
Environmental Impact
- AquaticToxicity
- Toxic to aquatic life. LC50 (fish, 96h): 100-180 mg/L. Forms acidic solutions.
- Biodegradability
- Reacts in atmosphere. Oxidizes to sulfuric acid. Not biodegradable.
- Bioaccumulation
- Does not bioaccumulate.
- SoilMobility
- High mobility as gas. Deposits as sulfates. Contributes to soil acidification.
- AtmosphericFate
- Oxidizes to sulfur trioxide then sulfuric acid. Major acid rain precursor. Atmospheric residence: hours to days.
- OzoneDepletion
- false
- ReportableReleases
- Water
- 1 lb to navigable waters
- Air
- 1 lb/day (CERCLA RQ)
Ppe Requirements
- Respiratory
- SCBA or supplied-air respirator for >5 ppm or unknown concentrations. Air-purifying with acid gas cartridge acceptable for ≤5 ppm with escape provisions.
- Eye Protection
- Chemical safety goggles, face shield for liquid contact
- Skin Protection
- Nitrile gloves for liquid contact (cryogenic hazard). Thermal protection for liquefied SO2.
Reactivity
- Stability
- Stable under normal conditions.
- Polymerization
- Will not polymerize
- IncompatibleMaterials
- Potassium chlorate
- Alkali metals
- Metal oxides
- Halogens
- Ammonia
- Acetylene
- Aluminum
- HazardousDecomposition
- Sulfur oxides
- Sulfuric acid mist
- ConditionsToAvoid
- Heat
- Moisture (forms sulfurous acid)
- Incompatible materials
- ReactivityHazard
- Reacts with water to form sulfurous acid (corrosive). Reacts violently with metal oxides and alkali metals.
Regulatory Classification
- UnNumber
- UN1079
- DotHazardClass
- 2.3 (Toxic gas)
- DotLabel
- Poison Gas
- NfpaCodes
- Health
- 3
- Flammability
- 0
- Reactivity
- 0
- Instability
- 0
- EpaHazardCategories
- Acute toxicity (inhalation)
- Skin corrosion
- Serious eye damage
- SaraTitleIii
- true
- CerclaRq
- 1 pound (0.454 kg)
Contaminants That Produce Sulfur Dioxide
Sulfur Dioxide is generated during laser ablation of sulfur-containing organic contaminants, sulfate-based mineral scale, and rubber residues. Heat exchanger and boiler tube cleaning in power plants is a common source. SO2 requires exhaust scrubbing and monitoring per OSHA PEL of 2 ppm to prevent respiratory irritation.
Chemical Properties
Molecular formula, CAS number, molecular weight, and chemical structure
- Type
- chemical_properties
- Id
- sulfur-dioxide-physical-data
Physical Properties
Chemical and physical characteristics
- BoilingPoint
- -10.0°C (14°F)
- MeltingPoint
- -75.5°C (-103.9°F)
- VaporPressure
- 2538 mmHg @ 21°C
- VaporDensity
- 2.26 (Air=1)
- SpecificGravity
- 1.43 (liquid @ 0°C)
- FlashPoint
- Not applicable (non-flammable)
- AutoignitionTemp
- Not applicable
- ExplosiveLimits
- Not applicable
- Appearance
- Colorless gas, colorless liquid under pressure
- Odor
- Pungent, suffocating odor @ 0.3-1 ppm
Alternative Names
Synonyms and chemical identifiers
- Synonyms
- Sulfurous anhydride
- Sulfur oxide
- SO2
- Sulphur dioxide
- CommonTradeNames
- OtherIdentifiers
- RtecsNumberWS4550000EcNumber231-195-2PubchemCid1119
Health Effects
Adverse health impacts from exposure to this compound
- Route
- inhalation
- Effect
- Respiratory tract irritation, coughing, shortness of breath, and bronchoconstriction
- Severity
- high
- Onset
- immediate
- Route
- inhalation
- Effect
- Aggravation of asthma and chronic obstructive pulmonary disease (COPD)
- Severity
- moderate
- Onset
- short-term
- Route
- eye_contact
- Effect
- Severe irritation, burning sensation, tearing, and potential corneal damage
- Severity
- high
- Onset
- immediate
- Route
- skin_contact
- Effect
- Irritation and possible chemical burns (especially with liquid SO2)
- Severity
- moderate
- Onset
- immediate
Personal Protective Equipment
Required safety equipment for handling this compound
- Respiratory
- SCBA or supplied-air respirator for >5 ppm or unknown concentrations. Air-purifying with acid gas cartridge acceptable for ≤5 ppm with escape provisions.
- Skin
- Nitrile gloves for liquid contact (cryogenic hazard). Thermal protection for liquefied SO2.
- Eye
- Chemical safety goggles, face shield for liquid contact
- MinimumLevel
- Level C for known <5 ppm, Level B for >5 ppm or liquefied SO2
- SpecialNotes
- Extremely irritating to eyes and respiratory tract. Cryogenic liquid causes frostbite. Asthma trigger - asthmatics extremely sensitive.
Exposure Limits
OSHA, NIOSH, and ACGIH exposure thresholds
- OshaPelPpm
- 5
- OshaPelMgM3
- 13
- NioshRelPpm
- 2
- NioshRelMgM3
- 5
- AcgihTlvPpm
- 0.25
- AcgihTlvMgM3
- 0.65
- WorkplaceExposure
- OshaPeltwa8Hr: 5 ppmstel15Min: nullceiling: nullNioshReltwa8Hr: 2 ppmstel15Min: 5 ppmceiling: nullidlh: 100 ppmAcgihTlvtwa8Hr: 2 ppmstel15Min: 5 ppmceiling: nullBiologicalExposureIndices
Storage Requirements
Safe storage conditions and compatibility
- TemperatureRange
- Store cylinders <52°C. Liquefied SO2 requires cryogenic storage.
- Ventilation
- Outdoor storage preferred. Indoor: mechanical ventilation with emergency backup. SO2 gas detection mandatory.
- Incompatibilities
- Potassium chlorate
- Alkali metals
- Sodium hydride
- Metal oxides
- Aluminum
- Halogens
- ContainerMaterial
- Steel cylinders. Stainless steel for liquid.
- Segregation
- Separate from incompatibles. Corrosive gas storage area.
- QuantityLimits
- Per fire code. Many facilities limit indoor storage.
- SpecialRequirements
- Cylinder restraints mandatory. Leak detection system required. Post "CORROSIVE GAS" signs. Emergency procedures posted. For liquid: cryogenic handling equipment.
Emergency Response
Procedures for spills, exposure, and incidents
- FireHazard
- Non-flammable. Cylinders may explode when heated. Toxic decomposition products in fire.
- FireSuppression
- If cylinder involved in fire, evacuate immediately - explosion hazard. Cool cylinders with water spray from maximum distance. Let fire burn out if possible.
- SpillProcedures
- EVACUATE. Ventilate area. SCBA for >100 ppm. Neutralize with soda ash or lime. Contain with dry sand or earth. For liquid: cryogenic hazard - specialized equipment needed.
- ExposureImmediateActions
- Remove to fresh air immediately. Eyes: flush with water for 15 minutes. If inhaled: administer oxygen. Seek medical attention - risk of bronchospasm and delayed pulmonary edema. For asthmatics: MEDICAL EMERGENCY.
- EnvironmentalHazards
- Major contributor to acid rain. Toxic to vegetation. Acidifies water bodies. Report releases >1 lb.
- SpecialHazards
- Severe respiratory and eye irritant. Triggers asthma attacks. Forms sulfurous acid with moisture. Corrosive to tissues. May cause bronchospasm and pulmonary edema. Cryogenic liquid causes frostbite.
Regulatory Classification
DOT, UN, and NFPA hazard classifications
- UnNumber
- UN1079
- DotHazardClass
- 2.3 (Toxic gas)
- DotLabel
- Poison Gas
- NfpaCodes
- Health3Flammability0Reactivity0SpecialnullInstability0
- EpaHazardCategories
- Acute toxicity (inhalation)
- Skin corrosion
- Serious eye damage
- SaraTitleIii
- true
- CerclaRq
- 1 pound (0.454 kg)
Environmental Impact
Toxicity, biodegradability, and environmental fate
- AquaticToxicity
- Toxic to aquatic life. LC50 (fish, 96h): 100-180 mg/L. Forms acidic solutions.
- Biodegradability
- Reacts in atmosphere. Oxidizes to sulfuric acid. Not biodegradable.
- Bioaccumulation
- Does not bioaccumulate.
- SoilMobility
- High mobility as gas. Deposits as sulfates. Contributes to soil acidification.
- AtmosphericFate
- Oxidizes to sulfur trioxide then sulfuric acid. Major acid rain precursor. Atmospheric residence: hours to days.
- OzoneDepletion
- false
- ReportableReleases
- Water1 lb to navigable watersAir1 lb/day (CERCLA RQ)
FAQ
Common Questions and Answers
As a laser cleaning operator, how can I protect myself from SO₂ exposure if the process generates this gas from sulfur-containing materials?
- Always prioritize engineering controls like local exhaust ventilation to capture and remove SO₂ at the source, maintaining exposure below the OSHA permissible limit of 5 ppm (parts per million) over an 8-hour shift. Wear a full-face respirator with an appropriate cartridge rated for acid gases (e.g., NIOSH-approved P100 with acid gas cartridge) and ensure personal protective equipment like gloves and protective clothing to avoid skin contact. Regularly monitor air quality with SO₂ detectors or badges, and evacuate if levels exceed 5 ppm, seeking fresh air immediately if irritation occurs.
Detection & Monitoring
Methods for detecting and measuring this compound
- SensorTypes
- Electrochemical
- UV fluorescence
- Infrared
- DetectionRange
- 0-50 ppm typical
- AlarmSetpoints
- Low2 ppm (NIOSH REL)High5 ppm (OSHA PEL/NIOSH STEL)Evacuate100 ppm (NIOSH IDLH)
- ColorimetricTubes
- Dräger SO2 0.1/a
- Gastec 5L
- Kitagawa 103
- AnalyticalMethods
- [object Object]
- [object Object]
- OdorThreshold
- 0.3-1 ppm - provides adequate warning below toxic levels
Reactivity
Chemical reactivity and incompatibilities
- Stability
- Stable under normal conditions.
- Polymerization
- Will not polymerize
- IncompatibleMaterials
- Potassium chlorate
- Alkali metals
- Metal oxides
- Halogens
- Ammonia
- Acetylene
- Aluminum
- HazardousDecomposition
- Sulfur oxides
- Sulfuric acid mist
- ConditionsToAvoid
- Heat
- Moisture (forms sulfurous acid)
- Incompatible materials
- ReactivityHazard
- Reacts with water to form sulfurous acid (corrosive). Reacts violently with metal oxides and alkali metals.
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