Proper ventilation is a crucial component in maintaining a safe confined space for Authorized Entrants.
Editor’s Note: This is first of a two-part series on the proper use of ventilation in confined spaces. In Part 2, coming in a couple of weeks, we will discuss the CRUCIAL final step you must take to ensure the safety of all who enter a confined space. Make sure that you read and follow all governmental regulations and manufacturers’ instructions regarding the proper use of all safety and construction equipment on all your job sites.
OSHA’s new standard for Confined Spaces in CONSTRUCTION — 29 CFR 1926, Subpart AA (published May 1, 2015) defines a confined space:
- Is large enough and so configured that an employee can bodily enter it;
- Has limited or restricted means for entry and exit; and
- Is not designed for continuous employee occupancy.
Examples specifically cited in the standards include — but are not limited to — storage tanks, process vessels, bins, boilers, ventilation or exhaust ducts, sewers, underground utility vaults, tunnels, pipelines, and open-top spaces more than four feet deep, such as pits, tubs, vaults, and vessels.
Essential elements of a Confined Space Entry Plan include:
- Hazard identification and elimination
- Atmospheric gas monitor(s)
- Personal Protective Equipment
Here in Part 1 we will focus on the basics of proper use of ventilation equipment during confined space entry.
The atmosphere inside a confined space can be significantly different from the air outside the space. Because of a lack of ventilation, air may not circulate properly inside the space. Deadly gases may be created or trapped inside the space, or there might not be sufficient oxygen. In other cases, there might be too much oxygen, or oxygen could be displaced by other gases entering or created in the space.”
Continuous forced ventilation, used with an atmospheric gas monitor, is frequently the best method of dealing with “bad air,” or potentially “bad air,” in a confined space.
The large volume of forced-in fresh air creates positive pressure in the confined space that, in turn, pushes contaminated air out. The forced air also creates atmospheric turbulence inside the space, which helps to dislodge pockets of bad air.
Applying positive pressure also helps minimize the chances of bad air seeping back into a space. At the same time, it reduces problems associated with drawing flammable gases back across the motor of the ventilator.
In a few cases, a combination of forced air and exhaust, or “suction” ventilation, might be desirable. For example, exhaust ventilation might be set up in a welding area, to capture fumes at the welding source. In other situations, a series of ventilators may be required to move air a long distance or ventilate a large area.
5 Factors to Consider
1. What is the size of the confined space and the airflow capacity of the ventilation blower?
Although OSHA does not define the number of times the atmosphere must turn over, many safety professionals recommend recirculating the atmosphere at least six times before entry, and at least six times per hour while the space is occupied. Note however that some state and local laws will require a higher turn-over rate.
For example, assume that a space has a volume of 3,000 cubic feet. Also assume that the ventilation equipment produces 1,000 cubic feet of airflow every minute (CFM). In this example, it will take three minutes to turn the atmosphere one time (3,000 cubic feet divided by 1,000 CFM of airflow). It will take 18 minutes to turn the atmosphere six times (three minutes per turn times six turns).
2. Will the exhausted gases be hazardous?
Always assume that the exhausted gases are hazardous. Locate the exhaust outlets in such a way that contaminants will not be drawn back into the confined space, and where air currents will disperse the exhaust gases quickly, without endangering other people. If the exhaust could be flammable, remove all ignition sources from the area.
Note: Special precautions are necessary in flammable atmospheres. Air flowing through a ventilation duct creates static electricity that can produce a spark. In a flammable atmosphere, such a spark can serve as an ignition source, resulting in an explosion or fire. Explosion-proof ventilation blowers may be required. In addition, proper grounding will be necessary to dissipate built-up static electricity. Consult the manufacturer of the ventilation equipment for specific instructions in these situations.
3. What is the source of make‑up air?
Position the ventilation blowers so there is a good supply of fresh air to pump into the space. Frequently, the best location for the intake is upwind of the opening to the confined space.
4. What about the duct?
The biggest factor that limits or restricts the performance of any ventilator is the duct.
Most portable air ventilation blowers utilize 8″ diameter flexible ducts. These ducts are usually available in standard lengths of 15 feet or 25 feet. Duct couplers are also available when longer lengths are required.
- Minimize the number of bends — Every bend, whether gradual or sharp, creates air friction, which reduces airflow delivery efficiency.
- Keep ducts as short as possible — Because of the effects of friction, airflow delivery is directly proportional to duct length. Longer ducts result in lower airflow delivery. Duct runs longer than 25 feet dramatically increase the size of ventilator required to produce the same airflow as a smaller ventilator with less than 25 feet of duct.
- Maintain the duct in good condition — Rips or tears in ducts will create blockage or leakage, resulting in lower airflow delivery. Also, a partially crushed duct will create friction that reduces airflow delivery. Likewise, dirt or grease inside a duct will reduce airflow delivery. Suggestion: To maximize airflow delivery and service life, store ducts in a container or rack when not in use.
- Position ducts to maximize air circulation — One effective method is to position the end of a duct on a cable rack or other support midway up a sidewall, with the duct pointed toward an end wall. This method will help to provide more even airflow distribution and more effectively ventilate corners where harmful gases or vapors might accumulate.
5. What kind of power source is available?
Sometimes there are few choices on a job site. Fortunately, blowers are available that are powered by gasoline, pneumatic, and electrical (12 volt DC, and 110 volt AC or 220 volt AC) motors.
Used in conjunction with training, hazard identification and elimination, atmospheric gas monitors, an emergency plan, and documentation, the right ventilation equipment is an important element of every confined space entry plan.
TrenchSafety offers training classes for you and your crews covering the “ins and outs” of the NEW OSHA standard for Confined Spaces in CONSTRUCTION. Give us a call at (901) 346-5800 or check our web site, TrenchSafety.com
Watch for Part 2, coming in a couple of weeks, in which we will discuss the CRUCIAL final step you must take to ensure the safety of all who enter a confined space.