MIL-HDBK-1191
surgery procedures usually involve a 6 L/min rate throughout the
procedure. Specialty applications (e.g. pediatrics) tend to demand
relatively higher usage rates. Because of these wide variations,
Designers shall closely coordinate with the Using Agency to establish
system demand and size satisfactory storage capacity.
Liquid Bulk-Tank Storage. Designers shall coordinate with
9.6.20.5
the Using Agency to consider the economic aspects of storage capacity.
Excessive capacity translates to higher utilization costs due to boiloff.
Too little capacity may lead to higher costs because of more frequent
tank refills, which includes vented oxygen cost as well as delivery fees.
Designers shall also consider the availability of oxygen refill service.
For remote locations, oversized capacity may be more practical and
economical to minimize deliveries and provide for unexpected consumption
increases. The selection between purchasing or leasing the bulk storage
tank and ancillary equipment shall be coordinated. Both economic and
logistic factors relative to the given supplier(s) shall be considered.
The standard tank sizes are shown in Table 9-15. The tanks are normally
leased with monthly rates typically ranging from 0 to 00. Life
cycle cost analysis will frequently show purchasing the liquid tank to be
the more economical choice. In evaluating the costs associated with
liquid services, be aware that the unit gas cost varies significantly
with total delivery volume, presently from
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.75 to
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.25 per gallon fora 1895 liter (500 gallon) delivery, to as low as
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.40 to
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.45 pergallon for 34,065 liters (9000 gallons).
Balance this consideration
with boil-off costs. The average daily boil-off rate is approximately
0.5% of total tank volume.
TABLE 9-15
OXYGEN BULK TANK SIZES
Gallons
Liters
1,895
500
5,680
1,500
11,355
3,000
22,710
6,000
34,065
9,000
41,635
11,000
49,205
13,000
68,130
18,000
75,700
20,000
Fill (or purge) losses associated with the tank refill process may be
significant. In tanks with a bottom-fill feature, gaseous oxygen must be
purged prior to refill to lower the tank pressure below that of the
delivery vessel, i.e. tanker truck. Depending upon local service
availability, there are tank types and filling equipment which can
minimize these losses. Top-filled tanks may be serviced without purge
losses, if filling equipment is available with suitable pumps for
overcoming tank pressure or utilizing the "top collapse" feature. These
should be specified when available. The top-filling procedure must be
conducted only by trained personnel to avoid uncontrolled system pressure
drop below minimum service levels.
System Monitoring. The central oxygen system design shall
9.6.20.6
facilitate oxygen system purity monitoring in accordance with DoD
Directive 6055.10 (reference 9w).
9-31
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