Class Code 4635
Oxygen Or Hydrogen Mfg
Class code 4635 covers employers who manufacture oxygen or hydrogen gas in California, including cryogenic air‑separation plants, electrolyzer shops, liquefaction and cylinder‑filling operations. Understanding this class matters because these operations carry unique high‑hazard exposures and a September 1, 2026 pure premium rate of $3.470 per $100 of payroll.
What Class Code 4635 Covers
This classification applies to operations that produce oxygen or hydrogen as the principal product: cryogenic air separation units that produce and liquefy oxygen, industrial electrolyzer stacks and balance‑of‑plant that generate hydrogen, compression and storage systems, cylinder and ISO tank filling, and on‑site quality control and laboratory testing tied to production. It covers plant operators, technicians who service compressors/cryogenic pumps and valves, instrumentation and controls staff tied to production systems, and the crews that fill, test and ship gas cylinders and dewars. It also includes routine maintenance activities inside the production process such as replacing seals on high‑pressure pumps, regenerating molecular sieves, and purging or inerting systems prior to repairs. Activities not directly related to manufacturing—such as third‑party retail cylinder resale or unrelated office work—may be classified separately.
Who It Applies To
- Industrial gas manufacturers operating cryogenic oxygen plants
- Hydrogen producers using electrolysis or reforming with on‑site compression/liquefaction
- Technicians who fill or test high‑pressure cylinders and ISO tanks at the production site
- Maintenance, instrumentation and compressor mechanics working on production equipment
- Quality control lab technicians performing gas purity and leak testing
Common Job Duties
- Operating and monitoring air separation units, electrolyzers, compressors and liquefiers
- Filling, testing, labeling and preparing cylinders, dewars and ISO tanks for shipment
- Inspecting and maintaining high‑pressure piping, valves, relief devices and pressure vessels
- Performing leak detection, gas purity analysis and corrective adjustments in the lab
- Executing confined‑space entries for vessel maintenance, purging and clean‑out
- Servicing rotating equipment (compressors, pumps) and performing hot work near enriched oxygen areas
- Performing instrumentation, control system tuning and electrical work on production equipment
Common Injury Risks
Understanding the $3.470 Rate
The September 1, 2026 pure premium rate of $3.470 per $100 of payroll represents the portion of premium that insurers estimate will be needed to pay expected workers' compensation losses for this classification. Insurers then add expense loads, assessments and profit margins; your final premium is adjusted by your company’s payroll size, experience modification factor (loss history), deductible choices and any misclassification corrections. Strong safety programs, low claim frequency, and accurate class assignment can materially reduce the premium you pay.
Cal/OSHA Compliance Requirements
Employers must implement Cal/OSHA‑compliant controls specific to compressed and cryogenic gases: written hazard communication, respiratory protection where oxygen or hydrogen atmospheres pose risks, confined‑space entry procedures, lockout/tagout for equipment servicing, and documented training on cryogen handling and high‑pressure systems. Facilities producing significant quantities of hydrogen or using hazardous process chemicals should also apply process safety management practices, leak detection and continuous monitoring, and maintain pressure‑relief and emergency venting systems per applicable Cal/OSHA and local fire code requirements.
How Key HR Helps Employers Under Class Code 4635
A PEO like Key HR helps employers in class 4635 by ensuring correct classification and payroll reporting, administering claims and return‑to‑work programs that limit lost‑time exposure, and providing standardized safety programs and training tailored to cryogenic, high‑pressure and flammable‑gas hazards. Key HR can also coordinate compliance audits, regulatory reporting, and access to group purchasing or preferred carriers that may lower administrative and insurance costs.
Get a QuoteFrequently Asked Questions
Are cylinder filling and distribution at a production site included in class code 4635?
Yes. Cylinder and ISO tank filling, testing and shipment performed at a facility that manufactures oxygen or hydrogen are typically included in 4635. Retail or third‑party distribution that only resells prefilled cylinders may be assigned to a different code, so classification depends on whether production/filling is part of your core operations.
What engineering controls most reduce the major hazards for this work?
Common effective controls include forced ventilation and classified ventilation for flammable atmospheres, continuous hydrogen and oxygen monitoring, intrinsically safe or explosion‑proof electrical equipment in hazardous areas, grounding and bonding during transfers, automatic leak‑detection and shutoff systems, double‑containment piping and robust pressure‑relief systems, and remote or automated filling to minimize worker exposure.
How can I lower workers' comp costs for a gas production facility?
Invest in targeted prevention: documented IIPP, task‑specific training (cryogenics, confined spaces, hot work), preventive maintenance for compressors and relief devices, proactive leak detection, early return‑to‑work programs, and partnering with a PEO for centralized claims management. These measures reduce frequency and severity of claims and improve your experience modification factor over time.
Quick Facts
- Class Code
- 4635
- Classification
- Oxygen Or Hydrogen Mfg
- Pure Premium Rate
- $3.470 / $100 payroll
- Effective Date
- September 1, 2026
- Source
- WCIRB Approved Filing
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