Safety within manufacturing plants is an ongoing issue that needs more focus and attention from those that are in charge of maintenance and safety. Combustion equipment can be a main source of explosions. These types of disasters are preventable even for someone who does not work with combustion equipment on a daily basis. What follows is no substitute for a skilled technician but it can help to save lives if someone is guilty of even one of the 10 deadly combustion equipment sins that follow. This screening takes less than 15 minutes. In each case the issue is spelled out along with the potential hazard.
All of the 10 "deadly sins" illustrated below are real-life examples of what auditors at Combustion Safety, Inc. have come across when asked to evaluate the safety of combustion equipment. All of these examples could make for a dangerous working environment that could result in a fire or explosion under the right conditions.
1) Tightness testing of safety shut-off valves and blocking valves is not being carried out.
The photographs show evidence of valve testing plugs that do not appear to have ever been removed. This is an obvious sign that the required gas train automatic valve tightness testing is probably not taking place.
Gas trains keep gas out of the combustion chamber when no combustion is taking place through a series of tight closing, specially designed shut-off valves that are spring-loaded to close. These are the safety shut-off and blocking valves.
Equipment codes and laws require these valves to be tightness tested on a regular basis. Auditors at Combustion Safety, Inc. find that proper checkouts and testing are seldom performed on the building code required schedules. Leaking gas through these valves into a combustion chamber can enhance the chances of an explosion.
2) Bad things can happen in control panels! Critical safety components can be mistakenly jumpered out and/or unreliable wiring or controldocumentation may exist.
The photographs show evidence of jumpered out safety components, poor wiring installations and/or poor documentation practices. (c) indicates wiring not labeled and not arranged such that it can be understood without a high probability of error. The wiring diagram shown in (d) has been customize in the field. This may or may not be accurate or correct.
Bypassing safety circuits is a big no-no. In the case of (e), an obvious electrical jumper wire bypasses a control. It is a wire that is not the same as the others, is connected with alligator clips and is of a different gauge and color. In (f) a popsicle stick is broken off and jammed into an air switch contact to hold it open. These are things to look for and find before trying to start equipment.
3) Obsolete burner management systems can make for long outages and less protection.
The burner management system in (g) is a new model RM7800 from Honeywell. An older electro mechanical model R4138 is shown in (h). Burner Management Systems (BMS) are the most important single safety component that exists for any piece of gas-fired equipment. Recent advances have put more features and safety into this equipment. For example, newer BMS have purge timers that are solid state and not adjustable. Many explosions have occurred where purge timers have been turned down in the field, making for ineffective removal of flammable mixtures before pilot light-off cycles have occurred. Another important issue is BMS obsolescence. If a BMS system or component fails that is no longer manufactured, it could take days of rewiring for a newer, different style to be installed.
4) Valves in the instrument lines can render switches / instruments ineffective.
Valves in instrument lines can be left in the closed position, rendering switches out of service and functionally incapable of operating. This could leave personnel and equipment unprotected. Valves should always be removed or at least locked open as soon as they are found. This especially applies to (i) high / low gas pressure sensing lines, steam pressure switches and water column connections.
5) Set points that are obviously wrong can render switches / instruments ineffective.
Instruments and / or safety devices without correct set points provide little or no protection. Gas pressure switches are shown that have set points pulled all the way to one side or the other. These are most likely not set correctly. Improper gas pressures could cause flameouts and explosions.
6) Flame roll-out (hard starting) can be a warning for dangerous conditions that may get worse.
When the bottom of equipment is burned or scorched, it may indicate flame rollout. This can occur when flues are partially blocked and / or fuel and air mixtures are set incorrectly. In these cases combustible mixtures and flames can exist outside of the firebox.
One of the risks is catching things on fire that are near the base of this equipment. Another is that as things continue to degrade, the flame rollout condition could turn into a catastrophic explosion from the accumulation of unburned gasses that ignite at once.
7) Automatic valve actuator failures (safety shut-off valve, blocking valve, pilot or vents) can make for hazardous operating conditions and down time.
Hydraulic valve actuator failures are sometimes indicated by the presence of hydraulic fluid on the valve's exterior. These photographs show oil stains on the sides of valves (m), puddling at the valve (n) and obvious excessive leakage (puddling under the equipment) (o). This condition it indicates that some of the actuator's hydraulic fluid has leaked. These valves are usually spring-loaded to close (not needing the hydraulic fluid for closing). The risk here is mostly one of equipment downtime when least expected since the hydraulic fluid is needed to open the valve to light the unit.
8) Lubricated plug valves can be leaking in the closed position or be frozen in place and inoperable.
Lubricated plug valves fail a number of ways, including leaking when in the closed position and being stuck in the open or closed position. Inspections at more than 200 sites found that more than 60 percent leaked in the closed position. A typical plug valve showing the body, plug and lubricant coating on the plug that makes the seal is shown in (p). A frozen valve that cannot be closed in an emergency is indicated in (q). Exterior stem corrosion is shown in (r). A valve that has been painted shut is shown in (t). A valve in the closed position that is leaking through the inside of the pipe downstream is indicated in (u). Lubricated plug valves need to be properly maintained on a regular basis. This means installing the proper sealant material and making sure the valves are exercised.
9) Vent valves can be failed open, disrupting burner operating conditions that put live fuel on roofs and sending improper mixtures into burners.
Normally open vent valves are installed in gas trains to improve safety when equipment is off (v). They allow gas leakage through the first automatic valve to get outside instead of to the firebox. When the burner tries to light, they are supposed to close tight so all the gas goes to the burner. If they are failed and leaking, they can vent natural gas from the gas train while the burner tries to operate (w). This makes for risks from ignition sources on the roof. It also makes for burners with unstable flames that cannot stay lit. If this happens, back-up systems must recognize the loss of flame and be called upon to shut off the gas. If these fail, an explosion is likely.
10) Outside vent terminations can be blocked with insect nests.
Most instruments and switches are vented with pipes outside to safe locations (x) to allow for proper operation and for gas to escape if a diaphragm failure occurs. Vent terminations are often found to be blocked with insect nests (y). A clogged vent can mean that there is no protection from leaking safety shut-off valves / blocking valves or for relieving failed components. Safety codes require protected vent terminations (z) be installed with screening devices.
Gas And Combustion System Explosions Can Be Avoided
For companies that are combustion system sinners, salvation can often be found in the form of awareness and training. It is also most likely going to take a culture change at the facility and a new found respect for combustion equipment. Consider the case of a 100-gallon water heater. The energy stored in a 100-gallon water heater can be equivalent to 10 sticks of dynamite. If a company has10 sticks of dynamite stored at its facility, it would treat the dynamite with respect. Combustion equipment is not like fall protection or employees wearing safety glasses. This equipment has the power to destroy people and property on a massive scale. It only gives one chance. That chance can mean death and destruction for those that may be working on or near the equipment, as well as many innocent bystanders. Companies must find 15 minutes to review their sites!
For more information, please visit www.combustionsafety.com or contact Combustion Safety at 1-888-826-3473.