MEDICAL GASES
Table 2. Oxygen – hospital mains and risers. Pipe size Pressure drop/100 Ft (PSIG)
1 1 1 1
⁄4 ⁄2
2” 2 1 3” 4”
” ”
⁄2 ”
1.05 0.99 0.90 0.66 0.58 0.33
Capacity (LPM) 2600 4000 8000
12,000 18,000 28,000
Number of ventilators @55 LPM Number of ventilators @10 LPM 47 73
145 218 327 509
260 400 800 1200 1800 2800
Note: This represents the maximum number of ventilators for a given section of the hospital served by the pipe sizes shown.
Numerous hospitals have projected and, in some cases, experienced actual demand increases of up to 20 times their historical average. This required significant investment for urgent upgrades of their bulk systems and pipelines
Typically, a vaporiser is a bottleneck.
Our experience with many projects and Requests for Proposals have shown that hospitals and health authorities would normally provide the historical average consumption and the projected average volume, but not maximum flow. Many would concentrate on the size of the tanks, but virtually no-one on the vaporisers capacity. However, the tank could be filled more frequently if the demand increases, while a vaporisers has a fixed capacity.
It should be noted that the nameplate
on a vaporiser provides the flow based on eight-hour use, which likely is not realistic for a hospital in a pandemic situation. It is best to consult with the manufacturer of the vaporiser for its continuous use productivity. The efficiency of the ambient air
vaporisers are also impacted by various environmental factors such as temperature, humidity, wind, and proximity to other structures that may block airflow.
A vaporiser would ice up starting from its liquid inlet. Typically, the suppliers would allow up to 50 per cent of the vaporiser covered with ice. The ice insulates the fins of the vaporiser and thus further decreases its efficiency, which might be a critical factor when the system has to operate at the top range of its capacity. Removing the ice is the easiest, quickest, and in the same time the most efficient method to stretch the typical system capacity. The most common methods are: l Mechanical removal of the ice coupled with power wash. This is quite an expensive method, which does not produce sustainable results. Facilities may have to use it if the ice bulb became too large.
l Installing of the industrial fan to increase airflow to the fins. This is an inexpensive and sustainable method. Its effect, however, is relatively minor. We speculate that an explosive-proof source of warm air would be more effective. We have not, however, seen any example of it being used by the hospitals.
l One of the most effective methods we have seen involves installation of the water sprinklers around the vaporisers. It is capable of producing sustainable results and virtually eliminating icing of the vaporiser even if the use exceeds its specified capacity. Unfortunately, it may only be suitable during the warm season when the temperature does not drop below freezing point. Facilities willing to consider this method should also make sure that water does not accumulates on the bulk pad.
Conclusion In summary, during the resilient design process, both the bulk installation and hospital pipeline are integral parts of the hospital oxygen system and must be considered as such by facility managers and consulting engineers.
Reference 1 Edward (Sandy) Renshaw, P.E.; Kaiser Permanente. Medical Air and Oxygen Capacity, March 29, 2020.
42 IFHE DIGEST 2022
IFHE
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