Carbon Dioxide Snow Cleaning
by Applied Surface Technologies
Safety Issues
Carbon Dioxide Snow Cleaning is considered safe to the user and environment but there are factors that must be addressed. Safety issues are:
1. Cryogenic exposure,
2. Carbon dioxide exposure and oxygen replacement, and
3. Environmental emissions
Cryogenic Exposure is a risk. The stream is cold, -80C. Exposure of the stream to your skin will freeze it, though not instantaneously. We have tested short exposures here and found no problems. Running the stream over your fingers poses no safety issues (we tested this on ourselves); while holding the stream on yourself at one spot will cause a problem after a few seconds. Exposure is similar to liquid nitrogen. The user will be instantly aware of exposure and will withdraw hand. Never aim the stream at another person. Please wear safety glasses when using this equipment. And follow all safety rules for using compressed gases. See your safety officer or call if you have questions.
Carbon Dioxide Exposure and Oxygen Depletion - If too much carbon dioxide enters your work area, your available oxygen decreases. But far more serious, is excessive carbon dioxide exposure. If you recall the movie Apollo 13, the CO2 buildup was a greater risk than the oxygen consumption. The same applies here. The CDC and OSHA has set some rules and they are discussed at this site (https://www.cdc.gov/niosh/npg/npgd0103.html). Though the page is confusing, the basic idea is workplace exposure should be maintained below 0.1% for the entire workday and short term exposures limited to 0.5% for short term exposures. The air we breathe normally contains about 0.04 percent carbon dioxide. Building codes may require sensors and air exchanges if the room carbon dioxide level exceeds 1000 ppm. A source of portable and fixed CO2 meters is at www.co2meter.com. These units run off of 12VDC or 120AC. Outputs include a small meter, 0 - 4 ma, 0-2.5, 5 or 10 volts, and a relay control and an alarm.
A design safety data sheet is duplicated below we found many years ago. It seems to have naval input
Maximum Limit - % Situation Remarks
.5 General Limit for 8 hr Threshold Limit Value (TLV) laid down by the American Conference of industrial exposure Government Industrial Hygienists
1. 90 day limit in nuclear Future design limit is 0.5%
submarines
3 Limit for short term exposure in Brain functions deteriorate above this level
in conventional submarine - Heavy Breathing, headaches
Maximum Limits For Carbon Dioxide Exposure
Effects of Continuous Exposure To Carbon Dioxide Over a Number of Weeks
Level Effect
0.5 - 1.0% Probably no significant physiological, psychological, or adaptive changes occur
1.0 - 3% Gradual changes in the composition of the blood and body fluids which may lead to irreversible changes in the tissues on prolonged exposure.
3% and above Deterioration in performance, alteration of basic body functions, and irreversible changes in the tissues
Please remember that outside of the US special rules, specific regulations on local maximum exposure rates, and health and safety suggestions might be applicable and have to be obeyed independently.
Please get a carbon dioxide sensor -- see above.
Environmental Issues for Carbon Dioxide Snow Cleaning are two fold - the local environment and outside emmisions. If you are removing hazardous material you must obey all the necessary rules for that substance. This means that the vent stream must be treated in the same way as the hazardous contamination would be treated. This can be filtering out the hazardous particulates, capture by other means, or whatever is safe as dictated by the safety officer. As an example, when one user cleaned an arsenic cap on GaAs, the work station was inside a special HEPA hood in a clean room, one that already had gallium arsenide and arsenic powders released.
With nonhazardous residues, the vent stream can be sent outside the building. There are no EPA rules on carbon dioxide emission from cleaning operations and there seems to be none on the horizon.
The carbon dioxide in cylinders comes from industrial vent stream. First, it is purified, then placed into trucks or cylinders for delivery. The largest domestic sources for carbon dioxide are food fermentation sites, large oil refineries, and chemical complexes. In England, the brewery industry sells its carbon dioxide vent for industrial uses. It is a form of delayed release.