Class Code 6251
Tunneling Or Underground Mining
Class Code 6251 covers tunneling and underground mining operations in California, including shaft sinking, drift and tunnel excavation, and associated underground support work. The WCIRB pure premium for this class is $5.297 per $100 of payroll, reflecting elevated severity and specialized hazards employers must manage.
What Class Code 6251 Covers
This classification applies to work performed primarily below ground: driving tunnels, adits, declines, shafts, raise boring, blind boring, and development headings in rock or soil. It includes crews installing ground support (rock bolts, steel sets, shotcrete), operating underground mobile equipment (jumbo drills, loaders, boggers), conducting blasting or controlled breaking, and performing underground utilities, ventilation, and dewatering. Surface activities are included only when directly related to underground operations (e.g., shaft collar work, underground material handling). Office staff, surface administrative personnel and unrelated surface contractors should be separately classified.
Who It Applies To
- Underground construction contractors (tunnel drivage and segmental lining crews)
- Shaft sinking and raise-boring companies
- Contract miners and subcontracted blasting crews
- Tunnel boring machine (TBM) operators and maintenance crews
- Specialty crews installing ground support, shotcrete, and grouting
Common Job Duties
- Excavating tunnels by drill-and-blast, TBM, or mechanical boring
- Installing ground support: rock bolts, steel ribs, wire mesh, shotcrete
- Operating underground mobile equipment (drills, scoops, loaders, conveyor belts)
- Ventilation system setup and atmospheric monitoring (gas, oxygen, particulates)
- Handling and placing bulk material, mucking and conveyor maintenance
- Preparing and executing controlled blasting and explosive handling
Common Injury Risks
Understanding the $5.297 Rate
The WCIRB pure premium of $5.297 per $100 payroll represents the portion of premium allocated to expected claim costs based on historical losses for this work. To estimate premium, multiply payroll by (5.297/100); for example, $100,000 in payroll yields a pure premium of $5,297 before insurer expenses, fees, and experience modification factors. Your final premium is affected by your employer experience modification (XMod), payroll audits, deductible/ex-mod programs, classification accuracy, and your insurer or PEO loading.
Cal/OSHA Compliance Requirements
Cal/OSHA enforces tunnel, underground construction and mining safety orders under Title 8, which require documented ventilation plans, atmospheric monitoring, ground support and roof-bolt standards, confined space procedures, and written emergency and evacuation plans. Employers must control blasting operations with permit and supervision requirements, provide respirators and hearing protection where needed, maintain daily underground inspections, and ensure worker training and competency for underground-specific hazards.
How Key HR Helps Employers Under Class Code 6251
A PEO like Key HR can help tunneling employers reduce workers' comp costs through accurate payroll classification, proactive loss-control programs, and coordinated claims management. Key HR provides site-specific safety consulting, mandatory training (confined space, respiratory protection, blasting awareness), return-to-work programs, and regular audits to lower experience modification and shorten claim durations.
Get a QuoteFrequently Asked Questions
Does Class Code 6251 apply to surface workers who support an underground jobsite?
Surface workers are classified under 6251 only when their duties are integral to the underground operation (e.g., shaft collar crews handling materials from the tunnel). Administrative or unrelated surface work should be classified separately to avoid overpricing.
What are the most effective steps to lower workers' comp premiums for tunneling crews?
Key steps include rigorous pre-employment screening, documented site-specific safety plans, engineered ground-control and ventilation systems, routine atmospheric monitoring, targeted training, strong return-to-work programs, and accurate payroll classification to ensure only true underground exposures carry this class.
How often does Cal/OSHA inspect tunnel and underground sites, and what triggers citations?
Cal/OSHA inspects based on incident reports, high-hazard enforcement focus, or planned programmed inspections. Common citation triggers include inadequate ventilation/atmospheric monitoring, missing ground support or daily inspections, deficient confined space procedures, and improper blasting controls.
Quick Facts
- Class Code
- 6251
- Classification
- Tunneling Or Underground Mining
- Pure Premium Rate
- $5.297 / $100 payroll
- Effective Date
- September 1, 2026
- Source
- WCIRB Approved Filing
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