SAFETY AND ENVIRONMENTAL CONSIDERATIONS continued
cryogenic freezer may contain an additional 3000–5000 cubic feet of gas, it is imperative for any area to have an effective oxygen-deficiency monitoring system. An example of how a typi- cal freezer area may be supplied with liquid is shown in Figure 1, while a schematic of how to integrate an oxygen-deficiency monitor with a remote display and audible horn and strobe is shown in Figure 2. The device shown in Figure 2 is well suited for continuous monitoring oxygen levels in areas in which inert gases or confined space may produce a hazardous reduction in the oxygen content of the air.
There are many technologies available to de- tect the level of oxygen. One with a long-lasting sensor that can accommodate temperature and barometric changes without false alarms would be ideal as there are some technologies that require frequent calibration or sensor replace- ment. The transmitter and sensor with local audible and visual alarm should be installed in a location where gas buildup or leaks are likely to occur or where released gases may accumu- late. It should be mounted no closer than 12 in. above floor level. Airflow within the monitored area, the characteristics of the gas (lighter or heavier than air), and the position of worksta- tions and personnel should all be considered in determining the most suitable installation.
At the entry to the area, a remote display and audible and visual alarm or strobe should be mounted to warn of any hazard before entry to the space is attempted. All it takes is a few breaths of an oxygen-deficient atmosphere for someone to lose consciousness. Though nitrogen is certainly the most prevalent cryo- genic liquid in a life science laboratory, the use of carbon dioxide for cell culture incubators, argon for instrumentation and blanketing of reactions, as well as oxygen for bioreactors, these gases can also present an oxygen- deficiency risk, or, in the case of oxygen, the risk of an oxygen-enriched environment that may cause normally nonflammable materials to ignite. In the case of oxygen-use areas, a monitor to detect when the oxygen level exceeds 23.5%, when it is no longer consid- ered an inert atmosphere, may be advisable. Approximate gas-to-liquid volumes for each of the above gases in liquid cylinders with their expansion ratio are detailed in Table 1.
OXYGEN DETECTOR MONITORING INSTALLATION
Remote Horn & Strobe 5803005
24VDC
Remote Display 5803004
4-20mA Power supply 4-20mA Figure 2 – Oxygen detector monitoring installation.
Table 1 – Approximate gas-to-liquid volumes for gases in liquid cylinders with their expansion ratios
Cylinder size N2
696:1 Lb of N2 (22 psig)*
Cu ft of gas at STP Gaseous liters STP
CO2 553:1 Lb of CO2 (350 psig)*
Cu ft of gas at STP Gaseous liters STP
Argon 847:1 Lb of argon (230 psig)* Cu ft of gas at STP Gaseous liters STP
Oxygen 862:1 Lb of oxygen (230 psig)* Cu ft of gas at STP Gaseous liters STP * Relief valve setting
387
3,383 95796
431 3,767 106670 528 4,615 130682 294 4,058 114910 327 4,513 127766 401 5,535 156734 160 liters 180 liters 230 liters
Supervised 4-20mA output to PLC or BMS
461 4,460 126294
513 4,961 140480
628 6,073 171969
379 4,577 129607
422 5,096 144303
517 6,244 176811
AMERICAN LABORATORY • 16 • SEPTEMBER 2014
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31 |
Page 32 |
Page 33 |
Page 34 |
Page 35 |
Page 36 |
Page 37 |
Page 38 |
Page 39 |
Page 40 |
Page 41 |
Page 42 |
Page 43 |
Page 44 |
Page 45 |
Page 46 |
Page 47 |
Page 48 |
Page 49 |
Page 50 |
Page 51 |
Page 52