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KILN CONNECTION: Safety First

February 1, 2007
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If you have a kiln, it is wise to take several safety steps. Sound like too much trouble? Can't afford the downtime? Then you could have a surprise coming from your kiln, and it will mark the worst day of your career.




"MythBusters" on TLC is one of my favorite TV programs. Lately, the show has taken an interesting turn-most of their myth-busting efforts seem to be associated with blowing things up. Whether they are blowing up buildings by igniting insect bombs, or breaking off the top of compressed air cylinders and shooting them through concrete walls, I love it all. I would quit my consulting business in a minute to be on the staff of that show!

Their controlled explosive experiments are pretty mild compared to the disasters that occur when kilns explode, however. During my career, I have seen several-in both tunnel kilns and periodic kilns-and the explosive force of natural gas is almost unbelievable. On one tunnel kiln that I saw, the buckstays (heavy I-beam steel that retains the crown) were literally bent in half, while the bricks from the crown were imbedded in the building roof. A periodic kiln that I observed had its doors blown open, and the entire kiln had been lifted off its foundation. The damage in both cases was extremely costly, and the downtime was crippling.

In checking many fuel control devices applied to hundreds of kilns, I have been astonished by the frequent disregard for safety equipment. Pressure switches that have been bypassed rather than replaced, and main fuel reset valves that don't close properly, are commonplace. I shudder when I look at systems like this. And even if all of the equipment is used correctly, sometimes it is so old that one can't help but wonder if it works properly.

Over the years, insurance and safety groups like FM Global and NFPA-86 have analyzed 'mishaps' and upgraded their standards. While some of the requirements seem to be redundant, their research into accidents has provided designs intended to deliver greater levels of security.

What Can You Do?

If you have a kiln, it is wise to take several safety steps. First, be sure that you understand the design of the fuel safety system. Whether you have an old FM valve check system or a brand new system with double solenoids and flame sensing, review the system carefully so you understand the function of each component. Then, working with your insurer, develop test procedures to insure that it all works properly. Sound like too much trouble? Can't afford the downtime? Then you could have a surprise coming from your kiln, and it will mark the worst day of your career.

Next, review the design of the system and compare it to current standards. Several very important items should be considered:

  • Does the kiln have a purge timer? Is it set to provide a minimum of four air changes before the kiln can be lighted? Has anyone calculated the proper time?
  • Does the system have double blocking valves on the main gas supply to the kiln? One valve is not enough, particularly when it is so old that it is probably leaky or unreliable.
  • Are the burners forced to light at minimum fire? The impact (no pun intended) of burners that light at high rates of fire is that unignited burners can quickly fill your kiln with an air/gas mixture that is within explosive limits.
  • Does each burner have two solenoid valves in series? I recently bubble tested over 30 ASCO solenoid valves on a kiln that was less than 15 years old, and every one of them had some leakage.


Make Kiln Safety a Priority

As companies try to minimize costs (translation: give everyone in the plant at least two jobs), kilns are not watched as closely as they used to be, and informed talent has often left for greener pastures. Subsequently, properly designed safety circuitry and devices become increasingly important to watch over the plant.

North American Manufacturing has estimated that as little as 27 cubic feet of natural gas is equivalent in fire power to a stick of dynamite. With many kilns having a connected capacity of 25,000 cfh, all of the burners set at high fire could deliver this volume of gas within four seconds. Repeated trials for ignition, which are sometimes necessary when burners do not light the first time, can quickly put the kiln mixture into explosive limits.

It is easy to ignore these issues when running a factory. However, if cost avoidance and safety are on your radar screen, you should consider auditing your kiln systems and maintaining them.

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