The Fundamentals of Confined Space Ventilation

Portable ventilation blowers have a single purpose of moving air, so even though they can be critically important to jobsite safety, they probably are not the first piece of equipment you consider. But while the concept of confined space ventilation may seem extremely simple, the typical application for a portable blower can require a considerable amount of thought and experience. A large percentage of construction professionals fail to respect this part of the ventilation equation, however, and unknowingly place workers’ safety at risk.

The usual presumption is that all ventilation blowers are basically the same because they move air. However, there are actually several different designs and configurations—some with specific features intended for special purpose applications. There is not a one-size-fits-all solution. Therefore, contractors must become better educated on the fundamentals of confined space ventilation.

Understanding Confined Space Ventilation

You must ask several questions before tackling a confined space application. Does the company have its own ventilation equipment? Does the contractor have to rent the proper blower? Do you know what blower is needed? These are all serious questions that require a solid understanding. But understanding this is often not a priority because most of the time, no one gets hurt when an incorrect ventilation procedure is used.

Using the wrong blower for the specific job application can cause significant problems. Efficiency and productivity can suffer without the proper knowledge, training or equipment. Approximately 100 people die unnecessarily each year from ignorance of confined space ventilation issues.

The majority of these tragedies can be prevented with education and the use of proper equipment. The first step is having a working knowledge of confined space ventilation fundamentals and procedures. Contractors can ask the blower manufacturer for help or contact their local safety providers. Even OSHA can be of assistance. The next step involves conducting the proper assessment to find the right solution for the job.

Where Do You Work?

The most important factor to consider is the location where a portable ventilation blower will be used. Is it hazardous or nonhazardous? Hazardous locations are clearly defined by the National Electric Code (NEC)—these sites con-tain flammable gases or combustible materials in the air. Obviously, gasoline tanks and utility gas plants are considered hazardous locations, but you may not realize that grain elevators, chemical plants and saw mills also pose a threat. It is important to discuss the concern of the hazardous location because deadly explosions can occur if the wrong equipment is used at these sites.

To help prevent accidents, manufacturers build hazardous-location ventilation blowers with aluminum or special plastic housings, which will not spark when contacted. They also incorporate a special motor. Since the combustion within a gasoline or diesel engine creates an ignition source, hazardous-location blowers are all powered by explosion-proof electric motors. While the name seems to suggest the blower is not capable of setting off an explosion in a hazardous atmosphere, that is not the case. An explosion-proof motor can still allow an internal explosion to occur. However, if this does occur, the structural integrity of the motor will hold up, and the unit will not burst into shrapnel.

The electrical wiring within hazardous-location blowers must also be certified by a listing agency, such as the Underwriters Laboratories Inc. (UL) or Canadian Standards Association (CSA). This means that the wiring system will not create a spark when plugging into an electrical outlet.

Lastly, these blowers use black-colored, statically conductive ducts, rather than the more familiar yellow or orange ducts. These special, black-colored ducts contain a carbon-based material that conducts an electrical charge, thereby reducing the chance that the static electricity discharge will cause a spark (a spark triggers an explosion). The yellow or orange ducts, on the other hand, cannot dissipate the buildup of static electricity; therefore, this dramatically increases the chance of a spark.

Do You Need a Permit?

Once the location has been established, the next consideration is whether a permit is needed. Any confined space that contains serious safety or health hazards requires a permit.

Permits document the atmospheric conditions of a confined space. To fill out a permit, jobsite personnel must test the atmosphere and document the readings. This formal process was developed to help protect workers from jobsite accidents.

Many larger construction firms and utilities develop their own written permits and protocols. For other companies, a good solution is to contact the blower manufacturer for copies of sample permits. No matter how they are written, all permits contain the same information and require the same questions to be answered.

Power Sources

Because of variations in jobsites, blowers are available with several different power sources—AC electric motors, DC electric motors, gasoline engines and even diesel engines. AC electric and gasoline-powered units make up the majority of blowers found in the construction marketplace since DC electric and diesel power sources are found mainly in niche markets, including utilities, offshore and barge service.

On jobsites with a readily available 115 VAC electric power source, blowers with AC electric motors often make the most sense. Because of carbon monoxide concerns, units powered by gasoline engines are typically reserved for outside applications when no electric power source is available. In those instances, the engine exhaust stream should always be positioned downwind from the blower intake to minimize carbon monoxide contamination.

Doing the Math

The next important factor in selecting a portable ventilation blower is the size of the confined space. The volume of the workspace combined with air recirculation regulations will determine the size and number of blowers needed. Since regulations vary, operators should consult their state safety laws to see how many times the air in a confined space must be circulated per hour.

Take, for example, a confined workspace with a volume of 4,000 cubic feet. The volume must then be multiplied by the hourly recirculation rate. If the law requires a minimum of six times per hour, the location needs 24,000 cubic feet of air to be moved each hour. To convert hours into minutes, divide 24,000 by 60, which equals 400 cubic feet per minute (CFM). Therefore, to meet regulations, a blower with at least a 400-CFM rating must be used, or a combination of blowers can be set up to equal 400 CFM.
Intelligent Design

To reach the required CFM, the design of the blower plays an integral part. Although these machines appear very simple, the engineering behind portable ventilation blowers closely mirrors the technology of jet engines. This is because both are available in axial and radial configurations. In a traditional axial configuration, air travels in a straight path through the blower—just like a modern jet engine. With a radial type blower, the air is moved in a circular rotation and then exits at a 90-degree angle to the intake.

Up to 2,000 CFM, radial configurations offer unsurpassed durability and performance for the physical size of the product. Additionally, if an electrical outlet is not available, radial-type blowers are the only available choice, as the axial configuration does not easily accommodate mounting an engine. However, with the enhanced thrust that axial flow configurations provide, they are an obvious answer for moving large volumes of air—generally above 2,000 CFM.

Airflow also depends heavily on the duct. The standard diameter for portable ventilation blowers is 8 inches, although larger sizes are available, and the most popular duct lengths are 15 and 25 feet. Duct lengths that exceed 25 feet significantly decrease the airflow that can be delivered to a confined space. Bends in the duct—especially those with an angle of more than 90 degrees—also reduce the airflow rates produced by any blower. Manufacturers understand that providing airflow in a confined space environment often requires making a minimum of two 90-degree bends in the duct, so they often account for the airflow loss when rating the CFM of their products. Be sure to check the specifications provided by the manufacturer for an explanation of how each specific blower was rated. Proactive manufacturers will provide certified airflow rates that are tested by independent laboratories.

While selecting a blower is not rocket science, it does require some careful consideration of the jobsite conditions and applicable safety regulations. Do not take the ventilation process for granted. Get to know the regulations and how they can directly affect your project. Becoming comfortable with the entire ventilation process will ultimately lead to finding the safest and most productive solution for the job.


Construction Business Owner, March 2011