According to the Centers for Disease Control & Prevention (CDC), 89% of confined space fatalities occurred with jobs authorized by supervisors, and 80% of fatalities happened in locations that had been previously entered by the same person who later died.

First things first: where manholes contain exposed, energized parts operating at 50 volts or more, the Occupational Safety & Health Administration (OSHA) requires anyone entering the manhole to be a qualified employee. Now, in order to be considered qualified an individual must have the skills and knowledge to:

• Distinguish live parts (from de-energized parts)
• Determine nominal voltage
• Calculate and maintain minimum approach distances
• Work with live equipment

Aside from OSHA’s Underground Installations standard, which always applies to a vault or manhole, safety pros can use these criteria to determine which other rules to apply:

Assume Highest Hazards

Start by considering every restricted space to be a “confined” space, governed by OSHA’s more stringent standard. Only if your inspection, testing, and monitoring reveal no hazards aside from electrical, can you apply the “enclosed” space rules. But to achieve the highest safety standards, some employers simply work all underground installations as “confined.”

Routine vs. Occasional Access

Unlike a confined space, an enclosed space is designed for routine entry, in non-emergency conditions.

Atmospheric and Non-Electrical Hazards

If inspection or site history suggests a hazardous gas mix or other non-electrical hazards: safety pros must apply OSHA’s more stringent “confined space” standard—unless the hazards can be eliminated. Vaults or manholes that might be expected contain such hazards require an entry permit and require even tighter safety rules.

Monitor Changing Conditions

If new hazards arise, the safety professional must again apply the stricter standard.

Vented Vault Exception

To enter a vented vault, if atmospheric testing verifies a safe gas mix, workers would apply OSHA’s "Alternate Procedure Entry" standard.

OSHA requires that the air be tested for dangerous gas mixes before entering an underground space. The hazards include oxygen deficiency, oxygen enrichment, and flammable or toxic gases. Work teams must test the air inside an underground vault or manhole before anyone enters. Workers can use a direct-reading meter and keep it calibrated within an accuracy of plus or minus 10%.

It is important to test for gases or vapors that are flammable, toxic, corrosive, or otherwise harmful. Workers are not particularly looking for methane or other combustibles, and carbon monoxide, and hydrogen sulfide. If flammable gas concentrations exceed 10% of the “lower flammable limit,” workers are in a hazardous atmosphere. Each regulated hazardous gas also has an acceptable concentration threshold.

If workers detect any hazardous gas mix, they should ventilate the work area to get its atmosphere within safe limits and monitor continuously, using an atmospheric detector. If ventilation fails to achieve a safe gas mix, workers may enter only by following OSHA’s stringent “Permit-Required Confined Space” rules. Those rules require written permission to enter, a written emergency plan, and breathing apparatus to ensure that no one is exposed to toxic levels exceeding OSHA’s allowable limits.

Oxygen concentrations below 19.5% are too low to breathe. Concentrations above 23.5% are “enriched” and potentially explosive. Before entering such oxygen-deficient or oxygen-enriched spaces, work teams must ventilate them and test to confirm that safe concentrations have been achieved.

Each of the OSHA standards for underground work has its own requirements. One person may fulfill all of these roles, but the industry best practice is to have any attendant meet the tightest standards and restrictions among all the OSHA standards. Attendants must maintain “reliable communications” with underground and other workers. Although voice communication might be adequate for shallow underground spaces, two-way radios are standard. “Reliable” means the crew must have a communications backup: spare radios, spare batteries, or mobile phones.

Employers must maintain a written Emergency Action Plan that specifies rescue and escape procedures. Designated rescue personnel must be appropriately trained. Employers must provide equipment for quickly and safely rescuing employees from the underground space. This means without injuring the rescuer, and without further harming the fallen employee. Crews should complete a job-briefing form and pre-entry checklist before entering the underground installation.