Key Safety Practices To Prevent Natural Gas-Powered Boiler And Firebox Explosions During Startup

5 February 2016
 Categories: , Articles


It's not uncommon for there to be a dozen or more fatalities per year due to boiler and pressurized vessel explosions in the United States. Many of these boiler-related accidents occur during the startup phase, and that is why it is important for boiler operators to take extra precautions when conducting a light-off. In addition, it isn't sufficient to be cautious during the startup alone; instead, safe operation demands that operators perform year-round, regular inspections and maintenance. Below are key safety practices that boiler operators should observe to protect themselves and others from injury and nearby property from destruction.

Ensure the boiler firebox contains no fuel

It doesn't take a lot of natural gas to create an explosive atmosphere; the lower explosive limit (LEL) for natural gas is only a little over four percent. That means even a seemingly-insignificant gas leak can permit an explosive gas accumulation to form inside a dormant firebox.

With that in mind, boiler operators must perform measurements of firebox air to ensure it doesn't exceed the LEL for natural gas. These measurements are conducted using gas detection meters, and they require careful use to prevent accidental ignition due to sparking. Be sure you or other operators have received the appropriate training in how to calibrate and use gas detection equipment.

If the LEL indicates there is a dangerous level of natural gas present, then you must conduct a purge to remove it. Once again, special care must be used when conducting a purge. Here are some guidelines for conducting a safe, effective firebox purge:

  • Inspect all vents for obstructions before activating a purge

  • Ensure that stack dampers are open

  • Turn over the volume of air inside the firebox several times to eliminate all combustible gases

Conduct regular valve and interlock inspections and maintenance

The gas train on a boiler is the entire series of gas valves and pipes that provide the firebox with a reliable, safe supply of fuel. A well-maintained gas train will protect operators from potential firebox explosions; however, a poorly-maintained system is a recipe for disaster. Gas valves can leak undetected unless they are inspected for proper valve closure and adjusted should they not close properly. As mentioned before, small leaks can add up when it comes to firebox combustibility.

Here are a couple of tasks that should be done to properly maintain and test valves inside the gas train:

  • Use the manufacturer recommended valve sealants to keep the internal seals well-lubricated

  • Conduct bubble testing to test valves for tightness when closed; this procedure requires proper technique to perform reliably, so obtain training for yourself or operators when needed.

Another aspect regarding boiler startup safety and the gas train is the interlocking system. Interlocks are simple in theory, though complex in operation. Operating as "checks and balances," interlocks monitor certain boiler parameters and prevent operation should the parameters fail to meet established standards. Interlocks must be inspected annually to meet regulatory requirements, but they are easy to neglect due to ignorance or apathy. However, a failed interlock can result in gas being introduced into the firebox and left undetected, thus resulting in an explosion.

Observe the firebox for proper operation immediately after startup

Once the boiler is lit, it may be tempting to relax. However, there is still a need for the operator to maintain a high level of alertness and monitor the firebox. Specifically, the flame status should be evaluated by the operator to ensure proper combustion; poor combustion allows unburned fuel to accumulate inside the firebox. Here are a few characteristics of a good flame:

  • All burner openings are lit

  • Flame color is primarily blue

  • The flames are "lively" in their motion

If you observe yellow, dull flames or dark burner openings, shut down the firebox immediately and begin purging operations to remove the unburned fuel. Then, conduct an appropriate inspection to determine the cause of the poor combustion before attempting to relight the fire.

For more information and tips, consider contacting your boiler manufacturer or a local supplier, such as Nationwide Boiler.