Fig. 2.

Results of the slow rate-loss trial. a The decrease in LN₂ weight (as a percentage of starting weight; blue line), and the corresponding increase in temperature (°C) over time (measured in days; red line) are shown. Thresholds for detecting a 10% weight loss and a temperature of − 185 °C are indicated by the gray and yellow lines, respectively. The interval between the detection of 10% weight drop and a rise in temperature to − 185 °C is 33.6 days and is indicated as the distance between the dashed blue and red lines. The rate of weight loss can be described by the formula W = − 2.778 t + 101.48 where W is the LN₂ weight (as a percentage of total) and t is the time (measured in days; R² = 0.9999). b Expansion of the period of time between days 33 and 43 shows a slight time interval between when the tank fully empties (blue line) and when the temperatures begin to rise (red line). The threshold for triggering the − 185 °C temperature alarm is indicated in yellow. The rate of temperature increase, shown as the change in temperature (°C) for each 15-min interval, is indicated in green