Dynamite Design for Hazardous Areas

Step inside a manufacturing facility, refinery or laboratory where toxic gases and materials are processed and discover some heavy-duty industrial engineering. For example, every electrical conduit is enclosed, the lighting fixtures are sealed and the fire-protection system is well-fortified.

11/01/2000


Step inside a manufacturing facility, refinery or laboratory where toxic gases and materials are processed and discover some heavy-duty industrial engineering. For example, every electrical conduit is enclosed, the lighting fixtures are sealed and the fire-protection system is well-fortified.

Why so extreme? Because inside such an environment, even one little spark could potentially blow up an entire building.

These highly specialized hazardous areas-and their classification-require extreme caution, innovative engineering and careful coordination among members of the building team and code officials for successful execution. Quite a tall order, but certainly one for which engineers have continuously proven to be up to the task.

Classify first, design later

According to Randy Turner, P.E., manager of electrical engineering at Lockwood Greene Engineers' Atlanta office, the first big challenge with these projects is compiling accurate definitions of all the hazardous materials in the space.

Armed with this information, the engineers can then classify the area appropriately-whether it's Class I, II or III-and begin to determine specific design requirements for each room, as delineated in National Fire Protection Association and National Electrical Code standards.

However, when all the hazards aren't carefully evaluated in the planning stages of the design, it often makes for an inefficient project.

For example, Ed Rotter, P.E., president of Rotter Engineering, Corpus Christi, Texas, mentions a case where engineers failed to take into consideration the hazard classification of pumps and installed them outside a facility, alongside a road. At that point, the only resolution was to permanently seal off the entire road because the potential of ignition by sparks from passing cars was deemed a hazard.

"With hazardous-area projects, haste makes waste," says David Drabish, P.E., a project manager with Sear-Brown in Cleveland. "You really have to take the time to consider these things, because in the long run, they show up anyway, and then you have to redo what you've already done."

Because owners have a tendency to change their minds about the equipment they want in a hazardous area, one approach is to overclassify and design according to more stringent requirements. However, this can be a very expensive solution, both in terms of design time and equipment. Further, in the event of an accident, the potential fines and citations can be a force to be reckoned with if officials were to discover that a space is lacking the required equipment based upon its hazardous-area classification.

"It can really hurt the business to have things misclassified," says Rotter.

In addition, Philip Granitz, P.E., a principal and the head of electrical engineering for HarleyEllis, Southfield, Mich., explains that it's very important for the engineer to be in close touch with reviewing authorities during the planning stages of a project to "make sure you're all on the same page," especially because there are many variations between different building codes.

Let's talk electrical

The main concern with any electrical equipment in a hazardous area is that all connecting points be sealed.

Consequently, Granitz explains, it's important to allot extra space for this equipment because the machinery has extra sealed-off fittings and enclosures, and tends to be more robust than conventional equipment.

Although the conduit seals are very effective in containing sparks, when it comes to maintenance, the devices are very difficult to work with, says Rotter. "It's a nightmare for maintenance because you usually have to break through the seal to do anything," he explains.

To avoid this, Rotter is a big fan of factory-sealed capsules. With these seals, a special fitting goes inside the conduit and wires run through the fitting, which is sealed with concrete materials. In the event of an explosion inside the seal, the concrete works as a barrier to prevent the sparks from traveling to other electrical equipment.

When lighting these spaces, the fixtures also tend to be bulkier and don't score high in the aesthetics department. In addition, Constantine Carros, P.E., a senior electrical consultant at Lockwood Greene Engineers' Atlanta office explains that these special fixtures must have temperature ratings that guarantee that the temperature will not exceed the equipment's flash point.

"The lighting fixture is considerably more rugged and more expensive," says Carros. "Also, you don't want to have to go and change the bulb every few months, so we typically use high-intensity-discharge, mercury-vapor or metal-halide lamps, which last much longer than incandescents."

Another approach is to keep the lighting source and other electrical equipment outside of the space, says Granitz.

According to Carros, "It's best to keep lighting fixtures, circuit breakers, panels, motor starters and wiring conduit out of the hazardous area, but that's not always possible."

When such devices must be housed in the space, intrinsically safe and spark-free equipment is an absolute necessity.

Striking a balance

Sometimes it can be less expensive to beef up the mechanical systems to adequately protect against hazards and invest less in electrical equipment, Granitz points out.

"In a recent lab project, instead of using an expensive starter and control panel, we used a standard control panel under positive air pressure to keep harmful vapors away," he explains.

Similarly, Turner claims that it's possible to reduce the hazardous-area classification if greater ventilation rates are utilized, because the rapid circulation of air prevents hazardous gases from building up. Ventilation is also used to pressurize a space in order to prevent gases from escaping into an adjacent area.

For fire protection, hazardous area requirements demand greater sprinkler densities and flow rates. Also, the installation of alarms sensitive to certain gases as an early warning device is often necessary, according to Dennis O'Beirne, an operations architect with Arcadis Giffels, Southfield, Mich. Another deterrent against smoke and gases is the use of higher ceilings.

"The higher the space, the more inherently safe it is because it allows for gases and smoke to accumulate high and allow people time to egress low," O'Beirne explains. "But a high space is generally not good for sprinkler activation. It's necessary to look at the total size and configuration of the space and apply computer technology to determine exactly what will happen in a life-safety emergency."

At the same time, O'Beirne points out that with recent improvements in sprinkler-head design, such as fast-response devices, sprinkler system quality and coverage area is improving.

Another big difference between hazardous-area design and that for conventional facilities is the time and expense required. According to Carros, just the electrical systems alone demand 10 to 20 percent more engineering. In addition, a chemical engineer must be brought on board, which also adds to the design costs. As far as construction goes, Carros estimates the price tag to be 50 to 100 percent more costly than a conventional project like an office building.

For example, Granitz points out that a standard 2-inch by 4-inch recessed troffer lighting fixture is less than $100, but for these projects, the sealed versions of the fixtures can be as expensive as $1,000.

Design alternatives?

One way to potentially cut down on facility costs, according to O'Beirne, would be to have more building jurisdictions allow for a performance-based life-safety design approach.

"If we have sprinklers and smoke exhaust, does that mean we still have to fireproof steel that's 30 feet high?" asks O'Beirne. "In total, all the systems working together can give an equivalent level of life safety."

In a nutshell, O'Beirne advocates new technology and engineering tools such as smoke studies, timed egress and the strategic location of sprinklers. If the systems are looked at as a whole, he believes that the life-safety intent of the code would be satisfied.

On the other hand, Granitz is of the opinion that performance-based design doesn't necessarily reduce expenses, but instead shifts the costs.

While engineers claim that technology advancements for building systems in such projects have not been significant in the past few years, there has been some improvement, such as in the areas of instrinsically safe devices and lighting fixtures.

In any case, hazardous area design should continue to evolve. Engineers can be expected to continue designing extremely safe, top-notch facilities to enable researchers and manufacturers to do their jobs in the endless quest to raise the quality of life for the industrialized world.





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