Low Oxygen Hazard In CA Storage
Symptoms of Asphyxia
Occasionally, someone must enter a CA storage to obtain fruit samples or to make equipment repairs. The atmosphere in the CA room contains less than 5% oxygen. Outside air is about 21% oxygen. Do you know what happens to you in a CA storage?
Symptoms of Asphyxia
17% oxygen--candle is extinguished
12 to 16% oxygen
breathing increased and pulse rate accelerated
ability to maintain attention and to think clearly is diminished, but can be restored with effort
muscular coordination for finer skilled movements is somewhat disturbed
10 to 14% oxygen
consciousness continues, but judgment becomes faulty
severe injuries (burns, bruises, broken bones) may cause no pain
muscular efforts lead to rapid fatigue, may permanently injure the heart, and may induce fainting
6 to 10% oxygen
nausea and vomiting may appear
legs give way, person cannot walk, stand, or even crawl. This is often the first and only warning, and it comes too late. The person may realize he is dying, but he does not greatly care. It is all quite painless.
Less than 6% oxygen
loss of consciousness in 30-45 seconds if resting, sooner if active
breathing in gasps, followed by convulsive movements, then breathing stops
heart may continue beating a few minutes, then it stops.
REMEMBER: THE CA STORAGE CONTAINS LESS THAN 5% OXYGEN
Before Sealing the Room
To avoid problems, plan ahead:
The manhole in the gaslight door should be at least 24x30 inches high to accommodate a large person with breathing equipment strapped to his/her back.
There should be a ladder inside the room, near the refrigeration unit. When loading the room, leave sufficient space to move and use the ladder around the equipment.
Place a danger sign on each gaslight door. "DANGER OXYGEN TOO LOW FOR PEOPLE TO BREATHE" or other suitable warning should be printed on the sign using letters at least 1-1/2 inches high.
Entering a Sealed CA Room
If you need to enter a sealed CA room (one from which you can be easily drag-rescued) proceed as follows:
Have at least 2 sets of tested breathing apparatus ready. If you don't own your own equipment, know where functional breathing equipment can be borrowed or rented. The breathing equipment should be fed with air (compressed or fan blown) not pure oxygen. The mask should be held in place with straps. Scuba diving equipment is dangerous to use because the mouthpiece may fall from your mouth if you fall.
Check the breathing apparatus. Does it deliver air to the mask? Is the tank full of air? The two individuals using the equipment should put on the breathing equipment in normal air and use up a tank of air while doing routine tasks. They can then become accustomed to the apparatus, learn something about it's limitations, and hear the alarm when the air level in the tank is nearly exhausted. The tanks should then be refilled prior to use in the CA storage.
Review the symptoms of asphyxia so you won't take any chances.
Remove the window in the gaslight door of the CA storage room.
The repair person enters the CA room with breathing apparatus. The back-up person must keep the repair person in sight. If this can be achieved from outside the CA room, the back-up person should be ready to enter the CA room, but not use the air until necessary. The back-up person may need to enter the CA room to keep the repair person in sight. If both people are in the CA room and one person's warning bell rings to signal the tank is almost empty, then both people should exit the CA room. If one must climb the ladder, the second should stay on the floor. If both need to climb the ladder to maintain visual communication, drag-rescue cannot be accomplished. Rather, open the room and vent with air.
If you vent the CA room with air and then need to restore the CA atmosphere, but do not have access to an oxygen burner, you can flush out the oxygen with nitrogen gas. Order the nitrogen gas in the liquid form (large thermos bottles), in trailer truck cylinders, or in regular cylinders with a manifold. A tightly packed room will require about 2 cubic feet and a room with plenty of free air space will require about 3 cubic feet of nitrogen gas per bushel to lower the oxygen concentration from 21% to below 5%. Use a garden hose to deliver the nitrogen gas to the intake of the blower in the CA room. Leave the porthole open to relieve pressure in the room.
G. D. Blanpied, Department of Pomology and L. D. Baker, Agricultural Engineering
Cornell University, Ithaca, NY 14853
Post Harvest Pomology Newsletter, 2(1):12-13