For safety, I use the Uvex Bionic face shield, which I bought from the Sanding Glove, and a small 3M 7500-series half-mask respirator with P100 filters (other half-mask respirators did not come small enough to fit my face properly—true for most women, I think). Even though I wasn’t wearing my face shield at the time, since my accident, I have looked into whether I could improve that protection. (I also wanted to find out how much protection my face shield would have provided.)
One of the possibilities I considered was the Trend Airshield Pro, which is very popular among woodturners. I discovered, however, that it claims to meet only the “low energy impact” standard for eye protection (http://www.trendairshield.com/specifications.html) and its stated respiratory protection is also lower than what I already have (and it is not NIOSH approved).
The safety standard for eyeglasses and face shields is specified in ANSI Z87.1-2010, which includes general specifications and impact specifications. It is the general specifications that the Trend Airshield Pro meets. My Bionic face shield is rated for the high-impact Z87.1 specifications.
I did the math (see below) and realized that, measured in kinetic energy, the mesquite missile that hit me delivered about 30 times the amount derived from the high-impact Z87.1 specs. Surely, my face shield would have absorbed some of that energy, but I almost certainly would have been injured anyway. Polycarbonate isn’t supposed to break or shatter, but all that energy would have had to go somewhere. Could I have escaped with bruising and a concussion? Would my face bones still have broken? Would the impact have contacted my eye? Does anyone have any experience they can share?
Anyway, I went further with my research and looked into ballistic face shields. These are expensive and heavy and seem to me like overkill (they are also not readily available to civilians). But they did lead me to riot helmets and face shields, regulated under the NIJ 0104.02 standard, with about 15 to 27 times the impact resistance specified under ANSI Z87.1. I ended up buying the lightest one I could find, the Max Pro RD1002X; it weighs 2 lb 3 oz, just a little more than the Trend Airshield Pro. Others weigh 3 lb or more, which I thought might be a bit heavy for prolonged wearing. I should receive it in a week and will report on how it feels.
You may notice that the impact resistance of the riot helmet is still not equal to the impact I sustained in my accident; at best, it is 15% too low. I balanced the impact resistance against potential comfort (weight) and cost and also reasoned that damage to this helmet would still mean considerably reduced damage to me.
My intention is to wear my Bionic face shield with my respirator when turning most things (most of what I turn is small and light), but to wear the Max Pro with my respirator when turning heavier pieces, especially when working with cracked wood. I also installed the wire guard that came with my Jet 1642 lathe and will see how that feels. I have read that others don’t like using it, but I’ll try it to see if it interferes with visibility or tool use.
For the technically minded among you, below is a summary of the kinetic energy figures derived from the specifications and my calculations. I give the foot-pound equivalents for kinetic energy for those more familiar with the units used in ballistic specs.
|KE Unit||Accident||Z87.1 High Velocity||Z87.1 Penetration||0104.02 Impact||0104.02 Penetration|
- velocity of falling object = √(2 × height from which dropped × acceleration due to gravity)
- kinetic energy = .5 × mass × velocity²
- 1-kg piece from a 10″- (.254 m–) diameter vessel turning at 1200 rpm
- velocity = (.254 × 3.14 (pi) × 1200) / 60 sec = 15.95 m/sec
- 1 kg traveling @ 15.95 m/sec
- .5 × 1 × 15.95² = 127.201 joules (93.82 ft-lb)
ANSI Z87.1 tests (Bionic face shield):
- High velocity:
- ¼-inch steel ball (.001046 kg) traveling @ 300 ft/sec (91.44 m/sec)
- .5 × .001046 × 91.44² = 4.373 joules (3.23 ft-lb)
- High mass impact:
- 500 gm (0.5 kg) pointed projectile dropped from 50 inches (1.27 m)
- velocity = √(2 × 1.27 × 9.81) = 4.99 m/sec
- .5 × .5 × 4.99² = 6.225 joules (4.59 ft-lb)
NIJ 0104.02 tests (riot helmet):
- 5.1 kg traveling @ 6.6 m/sec
- .5 × 5.1 × 6.6² = 111.078 joules (81.93 ft-lb)
- Penetration (pointed striker):
- 3 kg dropped from 3.00 m
- velocity = √(2 × 3 × 9.81) = 7.67 m/sec
- .5 × 3 × 7.67² = 88.243 joules (65.08 ft-lb)
This is a simplification, of course. The numbers don’t take into account air resistance, drag, pressure, or other factors. They just gives me a means of meaningful comparison.
Australia and New Zealand have higher impact standards. (Their medium impact standard is close to the ANSI Z87.1 impact standard—at least for eyeglasses. Cannot find their face shield specs.) Their test for high velocity uses a 6.35-mm (¼-inch) steel ball traveling at 120 m/sec. This yields a kinetic energy figure of about 7.5 joules, compared to 4 joules under Z87.1. The Triton Powered Respirator meets this higher standard, and its shield is indeed thicker than that of the Bionic face shield. I did not check the helmet or respiratory standards for this device.
Oops! The Triton respirator may no longer be available: I can’t find it even on the Triton web site.