The Basics of Ventilation, Part One: Overview


Greetings, fellow glassworkers!

This is the first in what will be a series of spotlight articles covering a wide variety of safety and technical topics for the glass studio. Throughout this document and those to follow, the issues discussed will adhere as closely as possible to meet and/or exceed any existing national (United States) codes (be it building codes, mechanical codes, electrical codes, recommended practice, etc.). Occasionally, a method of doing something will be pointed out as being outside the codes and if your studio is following a method like that described, you would be well advised to change your method to follow the codes.

The things that will be discussed in this series of articles will not be cheap, inexpensive quick fixes. Doing it right the first time is expensive. Nevertheless, it is better to do it right the first time than have an accident or, heaven forbid, a death. The books and videos never tell us what the real cost of glassworking is and that’s a shame. Our craft is a continuously evolving monster with many heads. There are so many directions that the glassworker can turn in their personal discovery of glass art that keeping up with safety and technology can sometimes take a back seat to the artists’ passion for their craft. The best example of this is our knowledge about ventilation.

We all know that ventilation is important, and that we all need good ventilation, but what IS good ventilation? What makes one design good and another one inefficient and unsafe? These are some of the questions that will be answered in the body of this article.

As flameworking artists, we take great pains to be sure we have adequate supplies of oxygen for our torches, a comfortable chair to sit in, good lighting and other creature comforts (gotta have our tunes, right?), but what do we do about providing good ventilation? Well, in reading some of the discussions in the on-line forum communities, I get the strong impression that many of our fellow lampworkers are doing absolutely NOTHING.

One lampworker wrote recently “Well, I just turn on the window air conditioner…but I keep on getting these headaches.” Another: “Just open up your windows. You’ll get plenty of cross-ventilation from any stray breeze.” And yet another: “Ventilation? What’s that? I work in a basement with no windows.”

Ok. Definition time.


1: the act or process of ventilating
2 a: circulation of air <a room with good ventilation>
   b: the circulation and exchange of gases in the lungs or gills that is basic to respiration
3: a system or means of providing fresh air

Definition number 3 is the important one. “A system or means of providing fresh air”. When we use our propane/air or propane/oxygen or natural gas/oxygen torches we are not only creating heat to melt our glass but also combustion by-products such as carbon monoxide (which is very rare),  and nitrous oxides (also called NOX). When the glass we use is heated to melting, rare earth and metal vapors are also added to the foul mix. All of these nasty contaminates must be exhausted from the room, preferably outside to an area where they can mix with fresh air and dissipate.

I have seen many comments from glassworkers who state, “I’ve got a CO monitor right next to my workstation and it’s never gone off”. This is not the basis for a good ventilation system. In fact, it is meaningless. Here is a direct quote from the ISGB Safety Manual, written by Stan Wolfersberger: “One of the most popular “urban legends” of beadmaking (or for that matter most glassworking operations, additional comment is mine) is that carbon monoxide is the principle agent to be worried about. However, in general this is not supported by actual measurements. The chief “bad actors” are the nitrogen oxides, especially nitrogen dioxide, which are produced by any high-temperature flame. In addition to producing the familiar “torch smell”, nitrogen dioxide is a severe respiratory irritant with a very low acceptable air concentration.”

Consider: we glassworkers use either fuel gas/air or fuel gas/oxygen torches to heat our glass. We range from reduction to oxidizing flames, but typically, most flames are neutral to slightly oxidizing. The presence of excess amounts of oxygen greatly reduces the possibility of carbon monoxide, which renders the issue of carbon monoxide being a problem to practically nothing. The only time you need to be concerned about carbon monoxide is when you are using a strong reduction flame, a flame that consists of fuel gas only – which results in a black sooty flame.

“But what about all the horror stories we hear every winter about people dying in their houses?” people might ask. This is a good question. The issue here is, once again, one of ventilation. Remember the definition: “A system or means of providing fresh air”. Every case where people have gotten sick or have died from carbon monoxide poisoning has been where the furnace or hot water heater has been faulty, the improperly or partially burnt exhaust fumes were not vented outside, but kept inside where they built up in concentration. There is a huge difference in scale when you compare the size of a glassworking bench torch to that of a furnace or hot water heater burner.

If it makes you feel safe to have a CO monitor nearby, keep it there. I am certainly not advocating the disregard of such devices; however, the likelihood of your glassworking torch generating enough CO to trigger the device, much less make you sick is vanishingly small. It is far more likely it (the CO monitor) will let you know if your studio furnace or hot water heater is malfunctioning.

So, what is a ventilation system? Any ventilation system (for glassworking purposes) consists of four components: A method of gathering and concentrating the fumes, a device for pulling and/or pushing those fumes (the fan itself), the ducting to route those fumes to the outside, and, most importantly, a source of fresh, clean air to replace the exhausted air.

Let’s examine each one of these components in turn.

A method of gathering and concentrating the fumes” refers to a hood or workstation enclosure. Before I discuss the individual types of hood arrangements, I’d first like to recommend that ALL glassworkers use a hood arrangement of some kind instead of an open duct. A hood is a critical device that is used to protect you from the process fumes and/or dust. Exhaust hoods induce airflow from the workstation area to the hood to remove contaminates or particulates from the work area. An open duct will only suck fumes and particulates from directly in front of the opening, not the surrounding area.

There are many different hood styles, but let’s look at just a couple of the more widely used methods:

  • Kitchen range hood– this method seems the most widely used, mainly due to its ease of purchase. However, there are issues with using an off-the-shelf range hood, the most important being the lack of suitable airflow through the hood. There are other issues as well – the small size of duct that the hood is designed to use and the lack of “baffles” or sides and back walls to further concentrate and gather the fumes. Many times, these issues can be overcome through creative at-home engineering. The fan can be removed and replaced, the sheet metal opened up and a proper sized duct adapter attached, and sheet metal sides and back installed as baffles.
  • Overhead (constructed) hood– this method is usually found in a teaching or professional studio where it is designed to cover a freestanding table where multiple torches are or can be used. This style hood can be constructed by a sheet metal professional, but can be built in the studio if you are handy with and have access to metal working tools. The airflow requirements for overhead hoods tend to be higher because of the freestanding nature of the design – they are usually between 4 and 6 feet above the table or workstation top and need higher air flow to ensure that the combustion by-products are sucked up into the hood. This style of hood also has the drawback of pulling a lot of room air through the hood, and tempering of the fresh air supply (this will be discussed later) becomes very important in more extreme climates.
  • Workstation enclosure– this method is also found in the professional or teaching studio, but is increasingly found in the home studio as well. The enclosure is typically constructed of sheet metal, again formed and shaped by a metal working professional, but can be built in the studio if you are handy with and have access to metal working tools. Designs vary, but the typical design is that of an open-ended box, with the opening facing the torch. The torch is placed so that the face of the torch is slightly back from the opening to allow space to manipulate tools and glass.

I’ve seen discussed on several glass-related forums an enclosure that was constructed using “foil faced foam board” on a wooden frame. Glassworkers thinking of emulating this design should be aware that the foil on the board is designed to act as an environmental heat reflector and insulation building component. It is NOT designed to be exposed to direct flame. Additionally, the foam material is isocyanine or some similar derivative, and when ignited, will generate poisonous fumes, not to mention the fact that a wooden frame will burn. Sometimes there is the strong urge to try to find other, lower cost or lighter weight materials. Be aware of the risks of using a non-standard material, such as foam board. This is a material that is designed as an outside-the-house insulating material. It is not designed to be used with or near an open flame. I’m sure the manufacturer of the material would be horrified with its use as described above. I strongly suggest and recommend that the glassworker stick with a metal enclosure.

A device for pulling and/or pushing those fumes” refers to a fan or blower. The process of moving air is a noisy proposition. There is no getting around this. The more air you move, the noisier the process. The best solution for eliminating, or at least decreasing to an acceptable level the amount of noise generated would be to move the fan outside, either on the side wall or roof. Many times however, it is not feasible to do this, both from a money and construction standpoint. Insulating the fan can help to a certain extent provided that air flow is provided so the fan does not overheat and burn up.

There are two basic types of fans: centrifugal and axial:

  • Centrifugal fans are most commonly seen in what is commonly referred to as “squirrel cage” fans. These fans operate by spinning the incoming air with a cage type assembly and using centrifugal force to exhaust it. The motor is typically outside the air stream.
  • Axial fans are seen in many places — if you have a computer, you’ve got at least one, usually in the power supply. Window fans are another example of this type of fan. These fans operate by spinning the air with blade type fan and exhausting the air along the axis of the fan. The motor is typically in the air stream, although some tube-type axial fans are available with externally motors.

For most glassworkers, centrifugal type fans are more efficient, less expensive, and provide a wider range of flows and air pressure.

I strongly recommend the use of Grainger Industrial Supply as a source of fans and blowers. They provide the technical information we need on all their fans in order to determine the proper fan for any given application.

The ducting to route those fumes to the outside.” Bad duct design is what causes most exhaust system problems. The single worst type of duct to use seems also to be the most widely used. Soft wall flexible corrugated ducting should never, ever, be used in any glassworking exhaust system. The reason for this bold statement is that the wall corrugations create turbulence in the air stream. Turbulence creates back pressure; back pressure results in loss of air flow, loss of air flow results in bad ventilation. It seems so easy to solve a difficult bend or twist problem in routing the ducting by using flexible corrugated ducting, but you should not succumb to the lure of an easy or quick fix.

Ducting should almost always be round, smooth-sided galvanized metal. I say almost always because there are times when rectangular ducting needs to be used, but most home studio needs can be met quite easily with round. This ducting is widely available at most home improvement stores, and can be had in a variety of diameters. I will discuss the importance of duct diameter in the design phase of this article.

A source of fresh air to replace the exhausted air.” Replacement fresh air is often overlooked by the do-it-yourselfer. The rule of thumb for replacement air is to provide fresh air at the same rate that combustion air is being exhausted. This means that if you are exhausting 400 CFM (cubic feet per minute) of combustion contaminated air, you also have to provide incoming fresh air at the rate of 400 CFM.

During the first energy crisis in the 1970’s, home builders and building code writers started to improve the design of houses to make them more energy efficient. One of the biggest changes has been to ‘tighten” up the houses or make them less prone to air leakage. Over the next 20 or so years, there seemed to be an increase in the amount of mold and mildew in houses and the next solution was to add in-house ventilation systems which provide fresh outside air, and exhaust used inside air. The net result of all these changes over the years is that there is much less air leakage and a much greater need to provide fresh air. Today, when mechanical systems are put into houses, the HVAC (Heating, Ventilation, and Air Conditioning) companies ALWAYS install a fresh air line into the house, usually somewhere near the furnace and/or hot water heater to provide make up air, or combustion air to these devices. This is current mechanical code across the United States. Current code also calls for the fresh air supply to be a minimum of 10 linear feet away from any exhaust duct.

What happens if you don’t supply any fresh air? If there is no fresh air supply available for the studio exhaust system, the exhaust system will pull the air from the surrounding room and building. The air pressure in the room and building will begin to drop. As we all know, nature abhors a vacuum. Air will begin to flow back into the room and building from anywhere it can. Usually, this will be an opening that already exists in the building – such as the vents for plumbing (which results in sewage smells permeating the building) or the exhaust vents for furnaces and hot water heaters (which results in nitrous oxides and carbon monoxides being drawn back into the house). Anywhere air can flow back into the semi-partial vacuum created by the exhaust fan, it will. Eventually, as the vacuum pressure falls, the fan will begin to stall and overheat, but you will notice the smells and odors from back flow long before that happens.

Those are the basic components of a ventilation system.

In part two of this article, I will discuss the math involved in designing your own ventilation system and walk you through several designs. (Don’t worry, if you have a basic calculator, you CAN do it yourself.) In part three, I will present an easy-to-build workstation vent hood that you can build yourself. Part four will discuss the adjustments to the calculations that need to be made if you live at high altitudes or for temperature extremes.

NOTE: This document is copyright (C) 2006-2015 by Michael Aurelius. Permission is hereby given to readers to use and reproduce this document for their own use only. This document may not be reproduced on any other website or forum without express written permission by the author.


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