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 just finished a massive update to the AVC (www.auralens.net) website. I’ve added somewhere in the neighborhood of 200 (or more) frames (if you count colors and sizes). We’ve got RED, Blue, Green, even PUCE (oh, god, why?). Plastic and metal. Some memory metals. Boring 1960’s retro designs as well as some cutting edge fashion frames. Did I mention RED? Men’s, women’s and unisex.
Oh, yeah, and I have RED frames!!!
Don’t forget, I’ve got a sale going on through the end of the month…http://www.auralens.net/discount_bts.cfm
Occasionally the question of ‘Glass or Plastic’ comes up in an e-mail, and I always advise the questioner that plastic (or polycarbonate) lenses are not a good choice for the glass working studio.
The reasons for this vary, but boil down to a couple of main issues:
1) Durability. Plastic/polycarbonate lenses WILL scratch, regardless of any supposed anti-scratch coatings. Let’s face it, the glass studio is about the worst place to wear plastic/polycarbonate lenses if you want to avoid scratches. Glass chips and dust are everywhere even if you are the cleanest glassworker in the world. All it takes is one small scratch (and it always seems to be dead square in the center of the lens!) .
2) Filtration issues. Despite the high-tech ability of plastic manufacturers, no one has been able to invent a dye that exactly replicates the multi-notch filter that didymium and ACE/AUR-92 provide. Let’s be clear (sorry, pun not intended): the notch filter at 575-590 nanometers is an absolute requirement to filter out sodium flare. This notch needs to be sharp and well-defined. If the notch at that point is too wide, you remove the surrounding wavelengths of light, which, of course, removes your ability to see those colors, which affects your color perception.
3) Fading issues. ALL plastic/polycarbonate dyed lenses fade. The manufacturer may claim that they won’t — but under what conditions are they making those claims? In a medical office or surgical suite? In an industrial setting? Have they tested the dye in front of a 2800 degree F torch for 8 hours per day, 6 days a week for a month? Most likely not. All of the dyed lenses that I have ever seen fade over time and exposure to torch light/heat, something that these lenses were NEVER designed for.
Plastic or polycarbonate lenses are inexpensive, and you get exactly what you pay for. You will have to replace them frequently as they get scratched and faded. Perhaps as often as every 4 months, depending on how much time you spend behind the torch. A good pair of glass lenses will last literally for years. An average pair of plastic so-called “borosilicate glassworker” filters cost $60.00. An average pair of glass full-coverage borosilicate glassworker filters cost $ 135.00. If you (conservatively) replace your plastic filters every 9 months due to scratching/fading, you will have paid for a pair of glass filters in 18 months, and the glass lenses highly resist scratching and absolutely will not fade.
The average pair of glass borosilicate glassworker filters will last (if you take good care of them) many years. Plastic/polycarbonate filters will last maybe as long as 9 months.
And, as an added bonus, you don’t require a separate add-on lens holder if you require a prescription. Glass lenses quite easily can have your prescription ground into the filter. Plastic/polycarbonate filters cannot.
The choice is always yours, and the best choice is the one that is made with all the information available.