Underground Storage Tank Closure: Safety Essentials for Inspectors

The Importance of Safe Underground Storage Tank Closure

Underground storage tanks (USTs) are being removed or permanently closed in increasing numbers across the country. Unlike in the past, modern tank closures involve regulatory procedures, paperwork, and often an element of danger. This is because many of these tanks have stored petroleum or other flammable products, adding an explosive dimension to the closure process.

As an inspector, you may find yourself in challenging situations during tank closures. Sites can vary greatly, and you might encounter contractors struggling with difficult removals in hot weather, with tempers running high. It's crucial to be prepared for potentially unsafe conditions and to know how to recognize and address them.

Understanding the Risks

The primary danger in tank closure stems from flammable and combustible liquids commonly stored in USTs. To work safely with these tanks, it's essential to:

1. Recognize the hazard
2. Evaluate or measure the hazard
3. Take action to control it

The Fire Triangle

To understand the fire hazard, we need to consider the fire triangle. This consists of three elements:

1. Fuel (product vapors from the tank)
2. Oxygen (from the air)
3. Ignition source

All three elements must be present for combustion to occur. Safe tank closure involves recognizing, evaluating, and controlling these elements.

Preparing for Tank Closure

Before dealing with flammable vapors, the contractor should prepare a safe workplace:

• Eliminate all potential ignition sources
• Mark utility lines, gas lines, and water lines
• Rope off the work area
• Ensure motorized equipment is properly grounded

As an inspector, verify that these safety measures are in place.

Removing Product and Dealing with Vapors

Once the workplace is secured:

1. Remove any remaining product from the tank
2. Drain product lines at both ends as they become accessible
3. Remove pipe and pump appurtenances, but leave the vent pipe connected

Understanding Flammability Range

Every product has a flammability range - the mixture of fuel and oxygen necessary to produce a fire or explosion when an ignition source is present. For most petroleum products, this range is between 1% and 10% concentration by volume in air.

Purging and Inerting

To eliminate or reduce flammable concentrations in the tank, contractors use two main methods:

1. Purging: Replaces flammable vapors with air
2. Inerting: Displaces oxygen and some vapors with an inert gas

Purging Methods

Purging can be done by:

• Blowing air into the tank through a diffuser
• Using an eductor to draw vapors out and fresh air in

Ensure that discharged vapors are vented at least 12 feet above the tank and away from the work area.

Inerting Methods

Inerting typically uses:

• Dry ice (frozen carbon dioxide)
• Compressed nitrogen

The goal is to lower oxygen concentration below 11%, the theoretical limit for combustion.

Monitoring During Vapor Control

Frequent monitoring is crucial during purging or inerting:

• Use a combustible gas indicator (explosion meter) for purging
• Use an oxygen indicator for inerting
• Take readings at the bottom, middle, and upper portions of the tank
• Clear instruments in clean air after each reading

Dealing with Sludge and Residue

Even after purging or inerting, sludge and scale in the tank can continue to emit vapors. This residue must be cleaned out, which can be done by:

• Tilting the tank to rinse and pump out sludge (for removal)
• Adding rinse water to dislodge sludge (for closure in place)

If more thorough cleaning is needed, ensure proper safety measures for tank entry:

• Test the tank space prior to entry
• Continuously ventilate the tank
• Provide respiratory protection

Closing a Tank in Place

If a tank is to be closed in place:

1. Clean the tank thoroughly
2. Fill it evenly with a solid inert material (sand or concrete)
3. Plug all openings
4. Disconnect and cap or remove the vent line

Safety Considerations for Inspectors

As an inspector, always prioritize safety:

• Wear appropriate personal protective equipment (PPE), including a hard hat
• Carry an explosion meter to check for dangerous vapor levels
• Avoid lingering at the ends of tanks (the weakest points)
• Stand at the end of excavations, not the sides
• Stay clear of the tank during removal to avoid potential equipment failures

Handling Leaks and Contamination

If you notice a tank has leaked:

1. Assess the environmental contamination
2. Consider safety concerns related to the leak
3. Evaluate the potential spread of contamination
4. Contact the local fire department if necessary

Transporting Removed Tanks

Before transport, ensure the tank is:

• Tested appropriately
• Permitted or labeled for transportation
• Plugged or capped, except for a 1/8-inch vent hole at the top

Most contractors transport only inerted or purged tanks. Transporting tanks in an enriched condition requires special considerations and may be subject to specific regulations.

Tank Disposal

Inquire about the contractor's disposal plan. Ideally, tanks should be taken to a scrap yard where they can be:

1. Cleaned (if not already clean)
2. Safely cut up for recyclable scrap

Some areas have specialized disposal yards that can properly handle tank contamination and safely process the tanks.

Key Takeaways for Inspectors

1. Conduct a preliminary history of the tank and site
2. Prioritize safety during site inspections
3. Know when to stop unsafe situations
4. Ensure contractors understand proper vapor handling
5. Be familiar with vapor and oxygen monitoring equipment
6. Know when to call in other experts
7. Verify proper tank disposal methods

Conclusion

Tank closure is a complex process with significant safety implications. As an inspector, your role in ensuring these closures are conducted safely is crucial. By understanding the potential hazards, proper safety procedures, and best practices for tank removal and disposal, you can help prevent accidents and protect both workers and the environment.

Remember, all it takes for an accident is the right combination of fuel, oxygen, and an ignition source. Your knowledge and vigilance can make these jobs safer for everyone involved, including yourself. Stay informed, stay alert, and always prioritize safety in underground storage tank closures.

Article created from: https://www.youtube.com/watch?v=PDVOADEz4NI