Altitude and air temperature make a substantial difference in the performance of any ventilation system. The calculations I have provided in the Ventilation Primer, Part Two, are based on sea level and 70 degrees F.
Overhead hoods have a problem: they are non-functional over most of the width of the hood. The only part of the hood that actually functions as designed is an area about 1-2” wide surrounding the suction duct. This is fine for small torches while making small beads, but what happens when you upgrade your torch and start working with larger pieces of glass?
Insertion of large pieces of glass into the flame plume deviates it and the open duct in your hood is no longer functional. And once you start working with powders, enamels and/or fuming, the only draw area is directly in line with the duct opening. How can the standard overhead hood be made to work more efficiently for the lampworker? Continue reading
Ok. We’ve talked about the basics, now let’s take a look at some basic design issues.
Exhaust System Design
So, where do we start? Well, let’s talk first about a couple of important numbers and calculations that have to be made first.
CFM: Cubic Feet per Minute. The amount of air that a ventilation system can move. It is based on how much air a given fan can move against a given amount of pressure.
Velocity: The speed the air moves inside the duct. It is measured in Feet per Minute.
Velocity Pressure: The pressure created by trying to force air at a given Velocity through a given duct size.
SP: Static Pressure. The total pressure against which the fan moves air. SP increases as the size of the duct decreases, with the addition of bends, and with any amount of turbulence. As SP increases, the efficiency of the fan to move air goes down, or, to state it differently, the higher the SP, the lower the CFM from design.
Loss Factor: A multiplier, usually fractional, that is the amount of friction induced by ducts. This is number is a constant for specific duct types and is usually presented in a look up chart form. The chart we will be using in all these calculations can be found in here: https://mikeaurelius.files.wordpress.com/2007/12/table1.pdf .
Each one of these numbers or calculations factors into the design of an exhaust system.
I will present several different designs to show how each affects the total design.
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.
As we age, the eye mechanisms age with us. And, on occasion, dry eye issues can crop up as well. As a group working with hot glass, we are additionally exposed to hot air plus air movement created by any ventilation we are using. Age + heat + air movement = pretty much everything needed for a good case of dry eye syndrome.
Note: I am not a doctor, nor do I claim to be one, nor do I play one on TV, the movies or the internet. However, I HAVE talked with thousands of glassworkers like you and from time to time they all experience episodes of dry eye syndrome that cannot be medically explained.
Here’s the consensus of what seems to work for most people:
- First and foremost: BLINK YOUR EYES. The brain will override the blink reflex when you are working on very small intricate work. You have to consciously override your brain and blink. The best way to remind yourself to blink is to make a sign for the back wall of your work area. Make it big, on white paper. Use a black marker and write the word BLINK on it. Don’t put anything else on it. Write BLINK in large letters. Place it in your visual range at the back of your work area.
- Get some good quality branded SALINE ONLY eye drops. DO NOT USE MURINE!! DO NOT USE HOMEMADE SALINE!! Murine and other similar products reduce the red in your sclera (white of the eye) by constricting the blood flow through the surface blood vessels. Homemade saline will contain bacteria and other harmful crap. Use only pure, sterile saline drops from a brand-name manufacturer. At the start of your glassworking session, put at least two drops in each eye, then blink several times to lubricate your eyes. During your session, take “safety breaks” every 45 minutes to an hour and repeat two drops in each eye, blinking afterwards. If you feel your eyes “drying out”, stop and add more drops.
- At the end of the session for the day, after you’ve safely shut down your work area, wash up, including your face and hands, then put two more drops in each eye.
Now, if the dry eye symptoms still continue after this, you may have an underlying medical issue and I strongly encourage you to visit your local eyecare provider.
I’ve been getting bombarded with requests lately from folks who wanted me to create a program or spreadsheet to do the static pressure calculations automatically.
The download location has been changed and you will now find it on the front page of the Aura eCommerce website. You must be a registered customer on the website in order to download it.
After you’ve completed the registration process, you will find it in the “Downloads” section of your account.
It’s in a zip file. Download it to a temporary file, unzip and click on the setup module. It will install like a normal windows program, and can easily be uninstalled from your control panel.
I *WILL NOT* be creating a version of this program for smartphones or for the cult of Apple.