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Vault and manhole incidents: Your key response strategies

Welcome to PPL Electric Utilities’ Tips of the Trade for first responders. These tips are intended to help you respond safely and effectively to incidents involving electricity. Please review with your team and visit our dedicated first responder safety website for additional materials.


To learn more about PPL Electric Utilities' response to COVID-19, click here.


Fires involving electrical facilities in underground vaults and manholes may be complicated by the presence of natural gas and other utilities. Overheated or burning cable insulation can “off-gas” potentially toxic or flammable gases that migrate through underground utility conduits and quickly build to combustible levels within these confined areas. When ignited, these gases may explode or burn, compromising other underground utility lines.

Such incidents place firefighters in proximity to conditions and atmospheres that are immediately dangerous to life and health (IDLH). You must exercise extreme caution when responding to underground vault and manhole fires.

First and foremost: DO NOT ENTER!

Regardless of its size, consider every manhole and vault a confined space containing potentially toxic gases, hazardous materials, and an explosive atmosphere. STAY OUT! Hazards may include lead, asbestos, PCBs, and toxic gases such as carbon monoxide, acetylene, and ethylene, among others.

Treat a combustible gas fire in a vault or manhole as you would a transformer fire: Let it burn and protect exposures while you wait for PPL Electric Utilities personnel to arrive and de-energize the circuit. Utility representatives can provide valuable situational awareness, including assessing the extent of potential gas migration and the probable location of any hazards in the manhole or vault.

Manhole incident do’s and don’ts

DO NOT open vaults or remove manhole covers. If a flammable atmosphere exists, opening the cover could bring the atmosphere into the explosive range.

Confirm that your dispatcher has notified PPL Electric Utilities.

Check for flammable gas concentrations near the vault or manhole to identify the level of hazard and determine appropriate evacuation zones.

Eliminate spark hazards.

Evacuate impacted structures nearby.

Establish a safe perimeter and reroute traffic.

Be alert for explosions, smoke hazards, and oil releases.

If there are no victims, let the equipment burn.

Never park over a manhole cover.

When water must be used to protect exposures, stay at least 100 feet away from energized objects. Use a 30-degree fog pattern at 100 psi—never a straight stream.

— If victims are involved:


Do not enter until PPL Electric Utilities confirms that all underground electrical equipment has been de-energized.


Wear full fire-fighting PPE and SCBA protective equipment and follow your department’s safety procedures for confined space rescue.


Test the atmosphere for toxic and flammable substances before entering.


Do not cause a spark.

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To report utility emergencies, call PPL Electric Utilities at 1-800-342-5775 (1-800-DIAL-PPL) immediately. For more first responder safety information, visit ppl.e-smartresponders.com.