Between the limits of enforcement and the potential sources of trouble, there’s a lot of room for something to go wrong with a boiler system. Consider the options for regular inspections, testing, and training to steer your facility clear of extra costs, outages, or much worse.

Combustion equipment safety is critical to the daily operation of industrial facilities and the safety of employees. However, this critical equipment is far too often overlooked or taken for granted.

Sure, every company maintains its equipment. But especially in today’s economy, employees are stretched thin and do not receive the kind of training and mentorship they did in the past. Equipment is also far removed from its optimum configuration after years of being cobbled together to “just run.” Over the years, while inspecting thousands of gas trains, we’ve seen our share of horror stories - often ending in fires and explosions. Alarms have been ignored and safety devices turned off. Once we found a Popsicle® stick shoved into a faulty air switch to keep the safety interlocks from shutting the machine down - a potentially deadly fix.

Our experience has been that little “poofs,” “pops,” or “pregnant boilers” are more prevalent than we’re willing to admit. Only major incidents with injuries and loss of life seem to make news. Headlines soon fade and rarely cause the follow-up attention required to highlight the pitfalls of poorly maintained and operated equipment.

There can be hundreds of minor incidents that occur for every one that ever gets reported or injures someone severely. Unfortunately, companies usually act only when some very large and tragic event occurs. Many people believe that explosions, fires, or outages from fuel-fired equipment only happen to others - that they are immune.

According to studies by groups such as the American Society of Mechanical Engineers (ASME), the National Board of Boiler and Pressure Vessel Inspectors (NBIC), and our own experience in the field, the major perils in operating automatically fired boilers are loss of water (low water), furnace explosion, overpressure, and overtemperature. The principal causes of accidents involving automatically fired boilers are lack of proper controls and safety devices, lack of adequate maintenance, and operator error, due to long periods of trouble-free operation.

Most facilities do not have personnel properly trained in combustion equipment maintenance, startup or shutdown procedures, and/or equipment operations. Most sites also do not follow proper interlock and safety testing guidelines, even when mandated by law. A number of states passed boiler safety laws to mandate boiler inspections hoping to remedy this. These are called jurisdictional inspections. However, in most states, these laws call for inspecting only the pressure vessel part of each boiler system. Inspections rarely address gas trains and/or fuel system issues. Interlock testing is usually assumed to be a responsibility of the owner, yet interlocks are among the most vital safety components for ensuring that your systems work safely.

Jurisdictional inspectors also following the letter of the law may limit the scope of the inspection. For example, in many cases, they can only evaluate equipment for compliance to the code that applied when it was installed.

There’s typically no screening for how far away grandfathered equipment is in the most recent codes. Equipment can pass this kind of inspection and be technically in compliance but also be nowhere near the current code’s level of safety or what is state-of-the-art for the industry.

Many large industrial clients are realizing that mandated inspections are not enough to protect their most important assets - the lives of their employees. Some of these companies now have combustion equipment safety programs that go well beyond minimal legally mandated requirements. These inspections include a detailed check of their combustion systems. This usually includes an analysis for code compliance, installation deficiencies, interlock testing, screening for maintenance practices that can be impacting safety, and assessing technological advances that can improve safety.


Think about the safety devices on a car. You have four brakes, an emergency brake, mirrors, windows, a horn, and headlights, to name a few. Then think about 50 to 100 cars sitting in a lot. Suppose that each of them has one of these features disabled. Would you enjoy those odds? How about driving every day for years in one of these cars? This is the type of risk you face if you do no annual testing and inspections of your combustion systems.

Gas trains help us to keep gas out of the combustion chamber through a series of tight, specially designed shut-off valves that are spring-loaded to close when no combustion is taking place These are the safety shut-off and blocking valves. Larger gas trains require dual valves and some also have a vent between these for added safety. The specific configuration that you have depends on your insurance and local code requirements.

Gas trains also have a number of components to make sure that safe light-offs take place and that shutdowns occur immediately if anything goes wrong during the operation of the equipment. They include a series of pressure switches that prevent gas under pressure that is either too high or too low being sent to the burner. They typically also have switches to make sure that airflows are correct for purging residual combustibles prior to light-off and that airflow is correct during operation.

Flame-sensing components also exist to make sure that flames are present when they are supposed to be there. Other components for sensing that the fuel valve is at low fire position prior to light-off may be present, along with furnace pressure switches, high-temperature limits, and/or water level cut-outs (depending on the type of equipment.)

All of these components are logically linked or interlocked to a burner management system, or BMS. The BMS is the brain that supervises and sequences all of the light-off efforts and sits and watches as the combustion processes take place. BMS systems manage the timing and adequacy of the purge prior to light-off and the time intervals allowed for getting pilots and main flames lit.

All this equipment is supposed to be checked on a regular basis by law, but with maintenance budgets among the first to be cut, proper checkouts and testing are seldom performed. Codes and manufacturers define what these frequencies are for different types of equipment.

Frequencies of required testing range from daily for some items like observing flames - assuming you know what to look for - to annually for some safety shutoff valve tightness testing requirements. It is in this frequency area that we find many problems in industry today.

Our typical circumstance is to find that no one is aware of regular testing requirements specified by codes. In most cases, we find that sites do some level of testing semi-annually or annually. The level of comprehensiveness varies depending on who is in charge and on that person’s knowledge of the equipment or systems.


There are two tests that must be conducted for each safety interlock device area. The first is an interlock function test. This verifies that a trip performs the correct interlock function that may be closing the gas valves or resetting the purge timer, depending on the device. The second test is the function test. This verifies that the device trips at the point at which it is set.

There are differing philosophies on what skill levels and which personnel should be performing this kind of testing at a facility. We have seen numerous types of programs within large commercial organizations in industrial facilities. The best chance of success is with a small group of individuals who receive intensive training and get the chance to do this kind of work frequently. You can’t give someone a few days, or even a week’s worth, of training but allow them to do the actual work once or twice a year and expect good, safe outcomes. There is just too much to know.

A lot of preparation needs to take place before testing of this type can safely proceed. This preparation includes having proper setpoint documentation for each of the components and having the right tools available. You should also have purge times that are calculated for the specific systems you will be evaluating.

You must also make sure that you have spare parts for the devices that will be tested. Remember, any failed device requires that the equipment be taken out of service until repairs are made. This must be a hard and fast rule clearly understood by everyone, regardless of production demands. Sometimes this style and type of testing must be carefully scheduled for times when repairs can be made. There’s a lot of liability in knowing that you have a failed component, and not making an immediate repair puts everyone at risk. You need to make sure that there are clear lines of communication and a plan for servicing/replacing failed components.

If you do not have a comprehensive program that includes detailed checklists, trained experienced professionals on hand to do testing and inspections, or a comprehensive reporting system, you are most likely at or near the high end of one failed item per piece of equipment level of risk. In our experience, those companies that have instituted a corporate-wide combustion safety program have reduced these component failures rates, greatly reducing unplanned equipment outages and explosions over a number of years.


Along with safety interlock testing of fuel trains, it is also required to perform annual leak checking, or tightness testing. Leaking valves have serious consequences. In the case of leaking vent valves, consider that burner pressure will be disrupted. Gas that leaks through the vent valve after the main regulator will make for a lower pressure and a leaner flame. Lean flames are often unstable flames and are subject to going out. This means that the low gas pressure switch and/or the flame detection system will need to be adjusted to work correctly. Every time this goes uncorrected, the site operates at a greater risk of catastrophe.

It can also be bad if the pilot valve leaks natural gas through to the firebox. Consider the case of a valve leaking at one cubic foot per hour, which is a lot, but not impossible. If the service is to a relatively small firebox, say a 200-hp firetube boiler, the mixture in the entire firebox could be at a flammable range in about two hours. This leaves room for a number of things to go wrong, like a less-than-perfect purge, a spark, and/or the mixture finding its way out of an exhaust opening or flue stack to an ignition source.

Besides the safety consequences, one cubic foot per hour of gas leaking though a solenoid valve costs the typical owner about $50 per year. Even this small a leak makes for bad economics, based on gas losses alone if a faulty valve is not changed out. Some large capacity equipment with higher pressure gas trains can lose hundreds or thousands of dollars a year worth of gas from a $200 valve.

Many solenoid valve failures we have seen have been due to dirt or debris lodging between the seat and the valve stem seal. Solenoid valves are usually designed with a flat surface to flat surface seal. The slightest amount of dirt or debris compromises this seal. Consider the fact that many vent lines extend outside of a heated plant facility. The change in temperature causes condensation from the air, and it runs down the insides of the vent line. The condensing water provides a means for rust particles and dirt to enter solenoid vent valves.

Being proactive about solenoid valves is an easy way to stay ahead of the risk curve. It’s one of the few proactive replacements you can do that actually can save you fuel dollars. In fact, some clients report saving tens of thousands of dollars in finding and repairing solenoid valves that leaked fuel.


Most explosions and fire incidents, by far, are due to human error. Knowing this and that organizations have a poor track record of changing behavior is why upgrades of safety systems and keeping up with code changes over time is important. The more that one can do to design in safety, the less one needs to be concerned or rely on human fallibilities. Still, all of the safeties and interlock equipment in the world won’t help if you attempt to short-circuit or jumper-out safety controls. There is no possible substitute for proper training.

A lot of plants and other facilities assume training is something that happens on the job in an informal sense. To them, it’s information that gets passed on from person to person over coffee or in between baseball scores. Training must begin when an employee starts a job, and then continue on a regular schedule. Training shouldn’t end after a couple days of orientation.

In putting together a training program, basic things that need to be decided include curriculums and hours per employee. New employees should be screened for their level of competence when it comes to operating or maintaining fuel systems or combustion equipment. There should be a plan in place to upgrade their knowledge and skills to levels that are deemed to be acceptable. In the case of boilers, there are requirements that operators will meet certain minimum levels of competence, such as being certified by National Institute for the Uniform Licensing of Power Engineers (NIULPE) or the American Society of Power Engineers (ASOPE). Additionally, some states and local jurisdictions have licensing requirements for boiler operators. There should also be consideration given to what supervisors and managers need to know to direct these people.

Training should include programs that create OSHA-competent staff for specific core needs such as natural gas and fuel piping systems or operators of ovens and furnaces. Many organizations do this online with web-based approaches. Training should include basics, equipment specific issues and mock hazard drills. Start-up shut down procedures should also be taught to staff and drilled regularly.

Training will need to be tracked and managed. Many organizations manage training with learning management systems. These are online web-based databases where online training is automatically logged.


No one will come directly to your site and force you to do safety interlock testing or tightness testing unless you are in one of the 27 ASME CSD-1 states or municipalities. Jurisdictional inspections are limited in their scope, and there is no other “code police” out there to check that you are in compliance. However, if an incident does occur and you do not have records indication you are in compliance with nationally recognized standards, you will be held accountable by your legal and/or insurance teams for not taking every possible precaution to prevent such incidents from occurring.

Still, the benefits of a proper annual inspection program greatly outweigh the costs. Being proactive in your maintenance of your fuel trains and combustion equipment improves the reliability of the equipment, leading to fewer unplanned outages and longer equipment life. It can mean greater efficiency by reducing gas leaks and keeping burners tuned. And most importantly, it means greater safety for your most important asset of all: your people. ES