Tunnel Safety - Cal/OSHA

Underground, the most dangerous thing in the heading is often the thing nobody can see: flammable gas, hydrogen sulfide, or air with too little oxygen. California handles tunnels with a separate set of rules, the Tunnel Safety Orders in Title 8, and it puts the state in the loop at three points federal OSHA leaves to the employer: Cal/OSHA classifies the tunnel for gas before work begins, the air is tested by a person the Division has certified, and the site has a safety representative the Division has certified. This Cal/OSHA Tunnel Safety Orders Toolbox Talk covers those three checks and the meeting rules that go with them.

Where the boundary of this talk sits#

This talk covers the California-specific parts of the Tunnel Safety Orders. Ground support, ventilation design, hoisting, compressed-air work, and specific gases have their own rules and talks.

The anchor#

Here is the distinction that carries this whole talk: in a California tunnel, the gas hazard is judged by the state before the crew goes in and measured by someone the state has certified while they work — Cal/OSHA classifies the tunnel as nongassy, potentially gassy, gassy, or extrahazardous from the geological information before bidding, tests are made by a Division-certified gas tester, and when flammable gas passes 20 percent of the lower explosive limit, all underground work stops and nobody goes back in, except for rescue, until the Division has authorized re-entry in writing — so the decision to go back underground after a gas event does not belong to the crew or the superintendent.

What the Tunnel Safety Orders cover#

Section 8403(a) applies the Tunnel Safety Orders to places of employment at tunnels, shafts, raises, inclines, underground chambers, and premises connected to them during excavation, construction, alteration, repair, renovation, or demolition. It also covers:

• cut-and-cover operations, such as subway stations, that are physically connected to ongoing underground construction and covered so as to create underground conditions;
• boring and pipejacking operations 30 inches in diameter or greater, with an exception for certain utility natural gas pipelines where no one bodily enters the bore;
• pipelines connected to or part of a tunnel where people work inside under conditions like a lined tunnel; and
• all shaft excavations intended to exceed 20 feet in depth where employees may enter the shaft or approach the shaft area — a shaft is treated as a shaft from its inception.

Under Section 8403(b), the Tunnel Safety Orders take precedence over other inconsistent safety orders at tunnels, except where the Compressed Air Safety Orders apply to work under pressure.

Classified before bidding#

Section 8422 requires the owner or agency proposing the tunnel to submit the geological information to the Division for review and classification. The preliminary classification must be obtained from the Division before bidding, and in all cases before underground construction starts. Labor Code Section 7955 sets the same four classes and says classification is to be made before bids are requested on public works projects whenever possible.

The four classifications:

• Nongassy — little likelihood of encountering gas during construction.
• Potentially gassy — a possibility that flammable gas or hydrocarbons will be encountered.
• Gassy — gas is likely to be encountered, or a concentration greater than 5 percent of the lower explosive limit of flammable gas or petroleum vapor is detected under the conditions the section sets.
• Extrahazardous — the Division finds a serious danger to employees, including concentrations of 20 percent of the lower explosive limit under the conditions the section sets.

A notice of the classification, and any special orders, rules, or conditions, must be prominently posted at the tunnel job site. The Division must be notified immediately if a gas or petroleum vapor exceeds any classification limit, and no underground work may advance until reclassification has been made.

Tested by a certified gas tester#

Section 8424 requires that tests be made by a person certified by the Division. In a potentially gassy tunnel, tests are made at least at the beginning of each shift and at least every four hours. In a gassy tunnel, tests for gas or vapors are made continually during operations. Where hydrogen sulfide is suspected, tests are made at least at the beginning and midpoint of each shift. Oxygen content is tested before other air contaminants. Records of gas tests and airflow measurements are kept on the surface and available to the Division.

Section 8424(c) is the stop rule. When any of the listed conditions is encountered — including 20 percent of the lower explosive limit of flammable gas or vapor being exceeded — all underground work shall cease, employees shall be removed, and re-entry except for rescue purposes is prohibited until the Division has been notified and has authorized re-entry in writing.

Section 8406(h) sets who can be certified as a gas tester, including at least one year of underground work in mines or tunnels, proficiency with gas detection instruments, and passing a written and oral examination administered by the Division.

A certified safety representative on site#

Section 8406(f) requires the employer, wherever the Tunnel Safety Orders apply, to designate an on-site Safety Representative who is qualified to recognize hazardous conditions and is certified by the Division. That person has authority to correct unsafe conditions and practices, or to stop the work if an imminent hazard exists, and is responsible for directing the safety and health program. Section 8406(g) sets the certification requirements, including underground safety experience and passing a written and oral Division examination.

Meetings: weekly on the job, monthly for supervisors#

Section 8406(e) requires supervisory personnel to conduct toolbox or tailgate safety meetings with their crews at least weekly on the job, with records of the date, time, personnel present, subjects discussed, and corrective actions. Section 8406(d) requires meetings at least once a month with supervisory personnel and foremen to discuss safety problems and accidents, also with records. Weekly is stricter than California's usual construction rule of every 10 working days.

California versus federal#

The federal rule, 29 CFR 1926.800, classifies underground operations as potentially gassy or gassy based on air monitoring and history, and requires the employer to assign a competent person to perform air monitoring. It does not require an agency to classify the tunnel, a Division-certified gas tester, or a certified safety representative. California requires all three.

Where the duty sits#

8 CCR 8403 sets the scope. 8 CCR 8422 and Labor Code 7955 set the Division classification, posting, and reclassification. 8 CCR 8424 sets certified gas testing, frequencies, records, and the stop-work rule. 8 CCR 8406 sets the certified safety representative, gas tester qualifications, weekly tailgate and monthly supervisory meetings, and the code of safe practices. For contrast, federal 29 CFR 1926.800.

What can go wrong?#

• The heading advances after a gas reading passes a classification limit, before reclassification.
• A foreman sends the crew back in after a 20 percent LEL alarm without the Division's written authorization.
• Tests are done by someone who has never been certified.
• The weekly tailgate meeting slips to every other week.

How do we manage this properly?#

• Know the classification — posted at the site, with any special orders.
• Test with a certified gas tester — oxygen first, then contaminants, on the required schedule.
• Stop at the limits — cease work, get everyone out, and wait for written re-entry authorization.
• Know the safety representative — certified, on site, with authority to stop work.
• Meet weekly and record it.

Before you start#

At the start of shift, ask what the tunnel's classification is, who the certified gas tester is, what the latest readings were, and who the certified safety representative is today.

Talk it over#

• What is our tunnel classified as, and where is the notice posted?
• What would you do if the gas alarm went off in the heading?
• Who can authorize us to go back in after a gas event?

The bottom line#

California tunnels are classified by Cal/OSHA before bidding, tested by a Division-certified gas tester on a set schedule, and watched over by a Division-certified safety representative. When flammable gas passes 20 percent of the lower explosive limit, all underground work stops and nobody re-enters except for rescue until the Division authorizes it in writing. Crews meet at least weekly.

Frequently asked questions about Cal/OSHA tunnel rules#

Who decides whether a California tunnel is gassy?

The Division. Under Section 8422, the owner or agency submits geological information and obtains a preliminary classification from the Division before bidding and before underground construction begins.

Download the Cal/OSHA tunnel safety orders toolbox talk PDF#

Download this Cal/OSHA Tunnel Safety Orders Toolbox Talk as a printable PDF in English and Spanish, and use it for this week's tailgate meeting underground.

Related toolbox talks#

• Confined Space
• Hydrogen Sulfide Awareness
• Carbon Monoxide Poisoning
• Emergency Response

Sources#

• Cal/OSHA, Title 8 CCR §8403 — Scope and Application ((a) tunnels, shafts, raises, inclines, underground chambers; cut-and-cover, boring and pipejacking 30 in or greater, connected pipelines, shafts intended to exceed 20 ft; (b) precedence, Compressed Air Safety Orders; (c) other safety orders): https://www.dir.ca.gov/title8/8403.html
• Cal/OSHA, Title 8 CCR §8406 — Injury and Illness Prevention Program ((a)–(c) safety suggestions and code of safe practices; (d) monthly supervisory meetings; (e) weekly toolbox or tailgate meetings with records; (f)–(g) Division-certified on-site Safety Representative; (h) gas tester certification requirements, written and oral Division examination): https://www.dir.ca.gov/title8/8406.html
• Cal/OSHA, Title 8 CCR §8422 — Tunnel Classifications (geological information to the Division; preliminary classification before bidding and before underground construction; nongassy, potentially gassy, gassy, extrahazardous; posting; immediate notice and reclassification): https://www.dir.ca.gov/title8/8422.html
• Cal/OSHA, Title 8 CCR §8424 — Airborne Contaminants (tests by a Division-certified person; potentially gassy at start of each shift and every four hours; gassy continually; hydrogen sulfide at start and midpoint of shift; oxygen first; records on the surface; (c) work ceases, employees removed, re-entry only with Division written authorization, including where 20% of LEL is exceeded): https://www.dir.ca.gov/title8/8424.html
• California Labor Code §7955 (Division classifies tunnels into four classes; before bids on public works whenever possible): https://codes.findlaw.com/ca/labor-code/lab-sect-7955.html
• OSHA, 29 CFR 1926.800 (federal: potentially gassy and gassy classification by monitoring; competent person performs air monitoring; no agency classification or certified gas tester): https://www.osha.gov/laws-regs/regulations/standardnumber/1926/1926.800

Written by FieldSafetyTalk's safety professional — a CSP, ASP, CHST and OSHA Authorized Outreach Trainer with 14+ years of international construction safety experience across federal, heavy civil, and industrial projects.

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