Hexavalent Chromium

Classification

Varies by compound; always check the supplier safety data sheet. OSHA's chromium (VI) standard (29 CFR 1910.1026(l)) requires classification to address at least cancer, eye irritation and skin sensitization. Many compounds, such as chromium trioxide, are also oxidizers and corrosive.

The pictograms shown (health hazard and exclamation mark) cover only the hazards common to Cr(VI) compounds as a group. Individual compounds often need more: chromium trioxide, for example, is also fatal if inhaled, corrosive, a strong oxidizer and very toxic to aquatic life, so its label adds the skull and crossbones, corrosion, flame over circle and environment pictograms (and drops the exclamation mark).

Hazards to expect on the label

• May cause cancer.
• May cause an allergic skin reaction.
• Causes eye irritation or damage.
• Further hazards depend on the compound.

Key precautionary statements

• P201 Obtain special instructions before use.
• P202 Do not handle until all safety precautions have been read and understood.
• P260 Do not breathe dust, fume or mist.
• P272 Contaminated work clothing should not be allowed out of the workplace.
• P280 Wear protective gloves, protective clothing and eye protection.
• P308+P313 IF exposed or concerned: Get medical advice or attention.
• P501 Dispose of contents and container in accordance with local regulations.

Limits are measured as chromium (VI) and cover dust, fume and mist from all Cr(VI) compounds. OSHA's standards (29 CFR 1910.1026 general industry, 1915.1026 shipyards, 1926.1126 construction) set a PEL of 5 µg/m³ as an 8-hour TWA and an action level of 2.5 µg/m³. Monitoring is repeated every six months at or above the action level and every three months above the PEL. NIOSH treats Cr(VI) as a potential occupational carcinogen with a REL of 0.2 µg/m³ (0.0002 mg/m³) as Cr over a 10-hour shift, 25 times lower than the OSHA PEL. The OSHA standards do not cover Portland cement, wood-preservative pesticide use, or work where objective data show Cr(VI) cannot be released at or above 0.5 µg/m³. ACGIH TLVs differ by compound; check the current ACGIH listing. State OSHA plans may set different limits.

Properties vary by compound. Chromium trioxide (chromic acid) is shown as an example.

• Appearance: Dark red, odorless flakes or powder; often used as a water solution. Other Cr(VI) compounds are typically yellow, orange or red
• Odor: Odorless
• Molecular weight: 100.0 (CrO₃)
• Boiling point: Decomposes at 482°F (250°C)
• Melting point: 387°F (197°C), decomposes
• Flash point: Not applicable; noncombustible, but it speeds up the burning of combustible materials
• Explosive limits: Not applicable
• Vapor pressure: Very low
• Specific gravity: 2.70
• Water solubility: 63% (CrO₃); some chromates are poorly soluble

Inhalation

Main exposures come from welding fume and hot work on stainless steel and high-chrome alloys, chrome electroplating mist, chromate pigments and paint removal. Cr(VI) irritates the nose, throat and lungs. Repeated exposure can cause sores inside the nose and a hole in the nasal septum.

Skin

Causes skin ulcers (“chrome holes”) where it contacts broken skin, and allergic contact dermatitis. Once a worker is sensitized, small amounts can trigger a reaction.

Eyes

Causes eye irritation and can injure the eye.

Ingestion

Harmful. Can damage the liver and kidneys; get medical attention immediately.

Target organs

Respiratory system, skin, eyes, liver, kidneys, blood

Long-term effects

Breathing Cr(VI) causes lung cancer. IARC classifies chromium (VI) compounds as Group 1, carcinogenic to humans. Liver and kidney damage and changes in white blood cell counts have also been reported.

Gloves

Chemical-resistant gloves suited to the compound and any solution it is in, chosen from the SDS. OSHA requires protective clothing and gloves at no cost wherever skin or eye contact is likely. See hand protection.

Eyes and face

Chemical splash goggles; add a face shield for plating baths and liquid transfers.

Respiratory

Use local exhaust ventilation and fume extraction first. Where respirators are needed, use them under a written respiratory protection program (29 CFR 1910.134). Above the NIOSH REL or at unknown levels, NIOSH lists a pressure-demand SCBA or supplied-air respirator, with a full-facepiece respirator with N100, R100 or P100 filters for escape.

Clothing

Coveralls or aprons suited to the task. Remove contaminated clothing at the end of the shift or task, and do not shake or blow dust off it. Bag it in sealed, labeled, impermeable containers for laundering or disposal.

Store in tightly closed containers in a cool, dry, well-ventilated area, separated from combustible and organic materials. Mark regulated areas where exposure may exceed the PEL and limit entry.

Use enclosure, local exhaust ventilation or tank covers and mist suppressants on plating baths. Clean with HEPA-filtered vacuums; dry sweeping, brushing or shoveling is allowed only where HEPA vacuuming has been tried and does not work, and compressed air only with capture ventilation or where nothing else is feasible. Provide change rooms and wash facilities, and keep food, drink and tobacco out of work areas.

Keep away from

• Combustible, organic or easily oxidized materials such as paper, wood, sulfur, aluminum and plastics (chromium trioxide can ignite them)
• Metals (chromic acid is corrosive to metals)

• Keep unprotected people away and avoid raising dust or mist.
• Wear a respirator, chemical-resistant gloves, coveralls and goggles.
• Keep spilled oxidizing compounds away from combustible materials.
• Collect solids with a HEPA-filtered vacuum or by moistening; absorb solutions with an inert absorbent. Do not dry sweep.
• Place in sealed, labeled containers; it may need disposal as hazardous waste. Keep out of drains and waterways.
• For chromium trioxide, refer to ERG Guide 141 (solid) or 154 (solution).

Suitable extinguishing media

• Use the agent best suited to the surrounding fire
• Water spray to cool fire-exposed containers

Special hazards

Cr(VI) compounds do not burn, but oxidizers such as chromium trioxide can ignite or intensify the burning of combustible materials. Fires can release toxic chromium-containing fume. Firefighters should wear SCBA and full protective gear.

• OSHA Hazard Communication (29 CFR 1910.1200): Hazardous chemical; labels, safety data sheets and worker training required. Classification must address cancer, eye irritation and skin sensitization.
• OSHA Chromium (VI), general industry (29 CFR 1910.1026): PEL 5 µg/m³ TWA, action level 2.5 µg/m³, exposure determination, regulated areas, protective clothing, hygiene, housekeeping, and medical surveillance for workers exposed at or above the action level 30 or more days a year, workers with symptoms, and anyone exposed in an emergency.
• OSHA Chromium (VI), shipyards (29 CFR 1915.1026) and construction (29 CFR 1926.1126): Same PEL and action level.
• CERCLA (40 CFR 302.4): “Chromium compounds” is a listed category, and many individual Cr(VI) compounds have their own reportable quantities. Check the table for the specific compound.
• DOT Hazardous Materials (49 CFR 172.101): Varies by compound. Chromium trioxide, anhydrous, is UN1463 (ERG Guide 141); chromic acid solution is UN1755 (ERG Guide 154).

• NIOSH Pocket Guide: Chromic acid and chromates
• OSHA 29 CFR 1910.1026 Chromium (VI)
• OSHA Fact Sheet: Hexavalent Chromium (OSHA 3373)
• 40 CFR Part 302 (CERCLA reportable quantities)
• IARC Monographs Volume 100C: Arsenic, Metals, Fibres and Dusts