Medical Gas Design
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IHEAProfessional Development Seminar No. 2 / 2006 Developments in the DesignAnd Installation of Medical Gases
DESIGN STANDARDS .
.
.
.
.
Presented by Geoff Hislop
.
.
.
.
.
DESIGNSTANDARDS
How many, how much and how safe. 1. INTRODUCTION The main requirements for medical gas systems are performance, reliability and safety. In Australia we have a comprehensive set of Australian Standards to use to achieve these ends. The main information missing from these Australian Standards is sizing data for medical gas piping.
2. AUSTRALIAN STANDARDS Some medical gas standards applicable are: AS 2896 – 1998 Medical Gas Systems – Installation and Testing of Non-flammable Medical Gas Pipeline Systems. AS 1894 – 1997 The Storage and Handling of Non-flammable Cryogenic and Refrigerated Liquids. AS 4332 – 2004 Storage and Handling of Gases in Cylinders. There are other standards referred to in these standards.
3. NUMBER, TYPE AND LOCATION OF OUTLETS The number and type of outlets is often set by the users to meet particular procedure requirements. Guideline requirements for many room types have been set out by Department of Human Services. These show information on the number of medical gas outlets and type of outlets required.
2
3
4
For those locations and applications where no diversity factor is nominated, AS 2896 gives a formula for calculating a diversity factor to be used for design.
1.3 F= log(10n )
Diversity factor
Where n is the total remaining number of terminal units on the branch or main Graphing the diversity factor against the number of outlets gives the following relationship 1.3 0.999208323 0.765169483 0.65 0.564964387 0.524802731 0.499604161 0.481665227 0.467937086 0.456926258 0.447798727 0.44004512 0.433333333
DIVERSITY FACTOR 1.4 1.2 1 Factor
1 2 5 10 20 30 40 50 60 70 80 90 100
0.8
Series1
0.6 0.4 0.2 0 0
20
40
60
80
100
120
Number of outlets
Notice that the diversity factor tends to be asymptotic towards 0.4 or 40%. All hospital systems need to have spare capacity in their design to allow for future increase in demand. This is likely to be conservative in practice, particularly for large systems. Use of a higher diversity factor does, however, provide a safety factor to allow for future increase in demand and connection of additional outlets.
4. PIPE SIZING Pipeline sizing is based on the flow rate required and a design maximum pressure loss from the source of supply to the last outlet.
5
Typical figures for use in pipe sizing for various medical gases are: Medical gas and medical compressed air
5%- 10%
Theatre medical compressed air
7.5%
Medical suction
10%
It is also necessary to know the design flow rate for outlets and the pressure loss through outlets. The following is extracted from AS 2896. Gas
Nominal pressure at terminal
Flow rate
Pressure loss across terminal
Medical air, oxygen,
375 kPa
250 l/min
100 kPa
Nitrous oxide, oxygen + carbon dioxide, carbon dioxode
375 kPa
40 l/min
10kPa
Surgical tool gas
1200 kPa
250 l/min
50 kPa
Suction, active gas scavenge
-55 kPa
40 l/min
15 kPa
entonox
6
Reticulation pipe sizing information for various gases flowing in pipes is not readily available and is not included in AS2896. One source of pipe pressure loss chart information is British Health Technical Memorandum No.22 “Piped Medical Gases, Medical Compressed Air and Medical Vacuum Installations”.
7
6. SUMARY OF DESIGN STANDARDS •
The basis of design for Medical gases should be AS 2896.
•
The sizing of piping needs to be based on flow charts suitable for the gas involved.
•
The total pressure drop of the piping system must be used as the basis for pipe sizing taking into account diversity and pressure loss of the outlet.
•
Pipe sizing should have an allowance in it for future capacity and installation of additional outlets for flexibility.
8
DESIGN STANDARDS .
.
.
.
.
Presented by Geoff Hislop
.
.
.
.
.
DESIGNSTANDARDS
How many, how much and how safe. 1. INTRODUCTION The main requirements for medical gas systems are performance, reliability and safety. In Australia we have a comprehensive set of Australian Standards to use to achieve these ends. The main information missing from these Australian Standards is sizing data for medical gas piping.
2. AUSTRALIAN STANDARDS Some medical gas standards applicable are: AS 2896 – 1998 Medical Gas Systems – Installation and Testing of Non-flammable Medical Gas Pipeline Systems. AS 1894 – 1997 The Storage and Handling of Non-flammable Cryogenic and Refrigerated Liquids. AS 4332 – 2004 Storage and Handling of Gases in Cylinders. There are other standards referred to in these standards.
3. NUMBER, TYPE AND LOCATION OF OUTLETS The number and type of outlets is often set by the users to meet particular procedure requirements. Guideline requirements for many room types have been set out by Department of Human Services. These show information on the number of medical gas outlets and type of outlets required.
2
3
4
For those locations and applications where no diversity factor is nominated, AS 2896 gives a formula for calculating a diversity factor to be used for design.
1.3 F= log(10n )
Diversity factor
Where n is the total remaining number of terminal units on the branch or main Graphing the diversity factor against the number of outlets gives the following relationship 1.3 0.999208323 0.765169483 0.65 0.564964387 0.524802731 0.499604161 0.481665227 0.467937086 0.456926258 0.447798727 0.44004512 0.433333333
DIVERSITY FACTOR 1.4 1.2 1 Factor
1 2 5 10 20 30 40 50 60 70 80 90 100
0.8
Series1
0.6 0.4 0.2 0 0
20
40
60
80
100
120
Number of outlets
Notice that the diversity factor tends to be asymptotic towards 0.4 or 40%. All hospital systems need to have spare capacity in their design to allow for future increase in demand. This is likely to be conservative in practice, particularly for large systems. Use of a higher diversity factor does, however, provide a safety factor to allow for future increase in demand and connection of additional outlets.
4. PIPE SIZING Pipeline sizing is based on the flow rate required and a design maximum pressure loss from the source of supply to the last outlet.
5
Typical figures for use in pipe sizing for various medical gases are: Medical gas and medical compressed air
5%- 10%
Theatre medical compressed air
7.5%
Medical suction
10%
It is also necessary to know the design flow rate for outlets and the pressure loss through outlets. The following is extracted from AS 2896. Gas
Nominal pressure at terminal
Flow rate
Pressure loss across terminal
Medical air, oxygen,
375 kPa
250 l/min
100 kPa
Nitrous oxide, oxygen + carbon dioxide, carbon dioxode
375 kPa
40 l/min
10kPa
Surgical tool gas
1200 kPa
250 l/min
50 kPa
Suction, active gas scavenge
-55 kPa
40 l/min
15 kPa
entonox
6
Reticulation pipe sizing information for various gases flowing in pipes is not readily available and is not included in AS2896. One source of pipe pressure loss chart information is British Health Technical Memorandum No.22 “Piped Medical Gases, Medical Compressed Air and Medical Vacuum Installations”.
7
6. SUMARY OF DESIGN STANDARDS •
The basis of design for Medical gases should be AS 2896.
•
The sizing of piping needs to be based on flow charts suitable for the gas involved.
•
The total pressure drop of the piping system must be used as the basis for pipe sizing taking into account diversity and pressure loss of the outlet.
•
Pipe sizing should have an allowance in it for future capacity and installation of additional outlets for flexibility.
8
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