A chiller has been standing under a dry nitrogen holding charge and a technician now has to climb inside the shell. What has to be done to the space first?
Correct Answer
A) It has to be ventilated with fresh air and the oxygen content verified before entry
Nitrogen is harmless to breathe in air and lethal in place of it. A vessel that has held a nitrogen charge contains no oxygen at all, and a person leaning into it can lose consciousness in seconds with no warning sensation. Bleeding the pressure off does not fill the space with air. The shell is force ventilated, the atmosphere is tested for oxygen, and the entry proceeds under confined space rules with an attendant outside.
Why This Is the Correct Answer
The hazard is displacement rather than toxicity, and nitrogen gives no warning at all because it does not smell, irritate or trigger the body's response to suffocation. Only forced ventilation puts air back into the shell, and only a meter proves it worked. Testing before entry and continuing to monitor during it is the practice that makes the entry survivable.
Why the Other Options Are Wrong
Option B: It has to be brought to atmospheric pressure and left open for the shift before entry
Opening a vessel does not ventilate it. Heavy gas layers sit undisturbed inside a shell for a long time with no air movement to displace them.
Option C: It has to be warmed with the water pumps so that the nitrogen rises out of the shell
Warm water in the tubes does nothing to exchange the atmosphere inside the shell, and nitrogen does not conveniently rise out of an opening.
Option D: It has to be swept with dry refrigerant vapor so that the nitrogen is displaced downward
Sweeping with refrigerant vapor replaces one asphyxiant with another and wastes refrigerant doing it.
Memory Technique
Nitrogen is not poison, it is absence. You do not smell it because there is nothing there to smell.
Reference Hint
A vessel that has held nitrogen contains no oxygen; it must be ventilated and its atmosphere tested before entry.
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