Carbon dioxide Snow Cleaning is considered safe to the user and enviromemnt but there are factors that must be addressed. Safety issues are:
1. Environmental emissions
2. Cyrogenic exposure
3. Carbon dioxide exposure and oxygen replacement.
Environmental Issues for Carbon Dioxide Snow Cleaning are two fold - the local environment and outside emisions. 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 particlulates, capture by other means, or whatever is safe. To date, only one user has been involved with a hazardous contaminate. In this case, the cleaning was done in a special HEPA hood in a clean room, one that already had gallium arsenide and arsenic powders released to the filters.
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 be none on the horizon. The Federal Registra, Vol 58, #90, on May 12, 1993, has approved supercritical fluid cleaning as a substitute for precision cleaning.
The carbon dioxide we use 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.
Cryogenic Exposure is a risk. The stream is cold, -80C. Exposure of the stream to your skin will freeze it. We have tested short exposures here and found no problems. Exposure is like liquid nitrogen exposure. The user will be instantly aware of exposure and will withdraw hand. Please wear safety glasses when using the equipment. And follow all safety rules for using compressed gases. See your safety officer or call if you have questions.
Oxygen Depletion and Carbon Dioxide Expsoure. 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 air we breathe normally contains 0.03 percent carbon dioxide. The concentration of carbon dioxide should be maintained below 0.1 percent. There are no rules on industrial sites, but common sense dictates a need. Building codes now require sensors and air exchanges if the room carbon dioxide level exceeds 1000 ppm (normal level is 350ppm). We can recommend one of 2 inexpensive portable CO2 meter. This unit will 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:
Maximum Limits For Carbon Dioxide Exposure
| Maximum Limit-% |
|
Situation |
|
Remarks
|
|
|
|
|
|
|
| 0.5 |
|
General Limit for 8 hr industrial exposure |
|
Threshold Limit Value (TLV) laid down by the American Conference of Government Industrial Hygienists
|
| 1.0 |
|
90 day limit for continous exposure in nuclear submarines (to be reduced to 0.5%) |
|
Future design limit for removal machinary is 0.5% |
| 3.0 |
|
Limit for short term exposure in conventional submarines |
|
Brain functions deteriorate above this level - Heavy Breathing |
Effects of Continuous Exposure To Carbon Dioxide Over a Number of Weeks
| Level - % |
|
Effect
|
| |
|
|
| 0.5 - 1.0% |
|
Probably no significant physiological, psychological, or adapative 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.
|
| 3.0 and above |
|
Deterioration in performance, alteration of basic body functions, and irreversible changes in the tissues. |
To my knowledge, no user has had problems, but please get a carbon dioxide sensor -- see above.
