Last month we examined the air quality problems created by solvent-based wide-format printers, and this month we’ll discuss four available methods of VOC removal and their respective pros and cons.
Ventilation/Exhaust: This method usually comes in the form of either running duct work outside of the room, exhausting directly out of the building, or a ceiling hanging filtration unit. It is the most widely recognizable method, although probably the least effective at VOC removal. VOCs are typically heavier than air and therefore hard for moving air to carry around.
All air filtration systems have a capture zone—a radius around the unit—within which contaminants will get sucked into the system and removed from the environment. These systems will have some effect on the overall air quality; unfortunately, very few VOCs will drift into the capture zone and be removed from the environment, thus creating a higher-than-allowable exposure limit environment. These systems can be costly and bothersome to maintain, and the EPA (Environmental Protection Agency) does not want these harmful contaminants exhausted out into the environment. These systems also often require special electrical hookups and building permits for installation—both make this method of VOC removal burdensome. Furthermore, fixed systems can limit your ability to rearrange your shop space or add more equipment as your needs change.
Source Capture System: these systems usually come as a box with hoses that attach directly to the printer and draw off VOCs, thus preventing them from escaping into the room. This proactive method is more effective than exhaust methods, but has several drawbacks as well. While it does keep a large percentage of VOCs from getting into the air, it cannot capture 100% of the VOCs produced by the printer, as VOCs off-gas from many points on the printer. Likewise, as the prints are rolling off of the printer they continue to off-gas, and will continue to off-gas when placed on drying racks.
Once the VOCs are out into the ambient air these systems are not able to remove them. Furthermore, once the printer is shut off, so is the source capture system, so any VOCs not already through the system will escape into the ambient air. In a test of a leading brand of source capture system on a popular brand of solvent based printer conducted by the California State Certified air testing company, the allowable exposure limit was exceeded with in as little as 30 minutes of printer operation, so while it did keep the level in the room considerably lower than with no filtration, it did not seem to be able to remove enough of the VOCs to keep the room below the allowable exposure limits.
Often companies must provide additional ambient air filtration when using a source capture system. Other downsides include expensive consumables and the size and bulk of the unit taking up floor space in the shop, as well as special electrical requirements.
Ambient Air Filtration: these systems are usually free standing units that draw air in through a filtration system and return the clean air back into the room through an exhaust outlet. The key to these units working effectively is that they must have enough air movement to circulate all of the air in the room, thus ensuring all VOCs in the ambient air are given a chance to pass through the filters of the unit. A small device may not move enough air to get all of the VOCs into its filtration system.
The drawback of this system is that it takes up floor space, much like the source capture system; however, in contrast to the source capture system, it can be easily moved around for more fluid movement of product and employees.
Another drawback is that this method is a reactive approach to removing VOCs. 100% of the VOCs get into the air before the device can remove them. However, if an adequately-sized ambient air filtration device is employed properly it can keep the exposure limits in a print room below the allowable limits.
Furthermore, this type of unit can be left running 24 hours a day and will continue to remove all VOCs produced from off-gassing created during drying times. On the ambient air filtration unit tested, the consumable levels were considerably lower than those of the source capture system, and standard 110v electrical power was required. This method has proven to be more effective than either ventilation/exhaust systems or source capture systems alone.
Source Capture & Ambient Air Filtration: this type of system acts as a dual purpose unit, and is the most effective of all the options available. It hooks up to the printer to remove VOCs directly—as with a source capture system—but will also circulate and remove VOCs from the ambient air in the room.
This hybrid device appears to be the best way to keep VOC levels well below the allowable exposure limits. By acting in a proactive manner to remove VOCs directly off of the printer the concentration of VOCs allowed to escape into the ambient air will be considerably lower than if you were just using an ambient air filtration system. And by reactively circulating and cleaning all of the ambient air in the room, any VOCs not removed by the source capture action or caused during off-gassing and drying will be removed in a short time frame, ensuring your shop remains OSHA compliant. Testing by the California State Certified testing company concluded that with this dual purpose air filtration system in place, the VOC levels in the room measured well below allowable exposure limits (see figures 3 and 4).
It is important to recognize that not all printers are able to support a source capture system. While most manufacturers recognize the need to provide exhaust ports on their printers, many printers are still freestanding units with no means of hook-up available. For those systems without pre-existing exhaust ports, utilizing an adequately sized ambient air filtration system would be the most effective method of VOC removal for ensuring OSHA compliance.
There are many factors that will determine the level of filtration required, such as room size, printer type, printer running speed, media size, color gamut utilized, printer running time, built in filtration/ventilation (HVAC), and type of inks used. It is the ultimate responsibility of the shop owner to ensure that adequate VOC removal is provided. The shop owner should be able to rely his or her equipment dealers to acquire the knowledge and expertise to make the best decision on what type of air filtration to install.
Solvent-based printers can be a very effective tool for any sized printing operation to expand the products and services they can offer, and to increase their business success. There are risks associated with solvent printer use, but these risks are not to be feared, they can and should be recognized and neutralized so that operators can function in a healthy and safe environment.
Larry Miller
Vice President
Island Clean Air, Inc.