I'm planning to wear proper PPE to dispense liquid nitrogen from a dewar directly into an insulated cooler filled with dry ice snow and this is my first time working with LN2. The technical objective is to reduce the temperature of the dry ice fifty degrees. My plan is to submerge the phase separator end of the hose in the cooler of dry ice, produce small amounts of LN2 intermittently, hand-mix the cooler of dry ice and monitor progress with an appropriate temperature probe. Do you have any concerns/comments on this approach?
should the room storing LN2 have ceiling exhaust or low level exhaust one says ceiling exhaust as nitrogen is lighter than oxygen to so extract effectively at high level; another says the when accidentally pouring some LN2 on the floor, low level exhaust can exhaust out nitrogen which is just been vapourized, not letting them even have chance to reach mid/high level of the room
I would suggest ceiling exhaust as the best option, if you have to choose. A properly designed lab or storage location should move air from a supply near the entrance to an exhaust near the highest hazard area (i.e. where the nitrogen dewars/tanks are). This creates directional airflow in the room and since, like you said, nitrogen gas is lighter than oxygen gas when temperature is equal, the nitrogen will be rapidly vaporized/warmed, rise towards the ceiling, and be pushed away from the entrance. If the tank/dewar is leaking the proximity to the exhaust means more rapid removal too. Ultimately though, you can run calculations based on room air changes per hour, room volume, and maximum total nitrogen content (when in gas phase at 1 atm) to determine the degree to which a catastrophic failure of a tank (or multiple tanks) might create a dangerous low oxygen environment. Those results will inform whether or not an oxygen sensor with audible/visible alarms is a good investment. If in doubt, purchase and install the sensor. It saves lives.
I would take this one step further. If there is no practical way to continuously vent the lab or room, treat the room as a confined space and have a oxygen level monitor either available before entering the room (not preferred) or a continuous level monitor with alarm outside of the area. As stated above you have to consider a catastrophic failure of the container and total evaporation of the liquid gas. While the danger is obvious in the case of liquid nitrogen, it is also true of liquid oxygen. If the oxygen content of an enclosed area is high, it becomes a significant fire hazard. Anything that is organic will vigorously burn in a pure oxygen atmosphere. The other comment I would make about the video is if you inspect a piece of safety equipment and find it defective (crack face shield or worn gloves) dispose of them immediately or remove it from the area and report it properly. You don't want someone else to use the equipment if it is defective.
