design of inert gas systems

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Home Design Guides Designing Inert Gas Systems

Design of Inert Gas Systems

Introduction

Inert gases, such as nitrogen are used on process plants for

a number of purposes - such as purging equipment and

inerting equipment. The most common inert gas used in

industry is nitrogen, but carbon dioxide and argon are also

encountered. Although usually non-toxic, inert gases can

displace oxygen creating an asphyxiating atmosphere. As

the common inert gases are colourless, odourless and

tasteless, they can build up in the atmosphere without the

victim being aware. This makes them very dangerous. This

article provides some guidance on safe inert gas system

design.

It should be noted that this is only an introduction to the

subject. The reader is advised to seek profess ional support

when designing an inert gas system.

Why Inert Gases are Used

Inert gases are used to create a non-reactive atmosphere, it

mus t be non-flammable and should prevent any adverse

chemical reaction. For example, providing an inert

environment to prevent the decay of food. Several industrial

gases are used for inerting. The most common is nitrogen, as

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accumulate. Gases that are heavier than air (such as argon)

will settle at floor level and at low points. The release of gases

with sim ilar densities to air (such as nitrogen) will tend to

result in localised regions of depleted oxygen. Particular

locations to consider are the following:

1. Gas storage areas

Inert gases are often stored in liquefied form. Spillages of

liquefied gas will rapidly vaporise, releasing large quantities of

gas. Ideally, storage areas should be well ventilated and away

from working areas. Access to the gas s torage area should be

restricted. The area should be equipped with gas monitoring

and display warning signs .

2. Relief and ventilation system outlets

Relief and vent lines should be clearly identified and should be

piped to a safe open air location, away from working areas.

3. Rooms where inert gases are used

Use of inert gases in enclosed areas should be avoided if at

all poss ible. They should be well ventilated and equipped with

oxygen monitoring equipment. Access s hould be restricted to

trained operators, preferably not working alone.

4. General access areas

General access areas (e.g. corridors) present a particular

hazard as there is no means of restricting who enters.

General access areas and inert gases not mix.

Other useful links

Gas pressure drop calculator spreadsheet

Electronic steam tables spreadsheet

Types of Pressure Relief Device

Ventilation

The designer needs to consider the likelihood of an escape of

inert gas and whether it will be adequately dispersed. Inert

gas systems which are outdoors rely on natural ventilation todilute and disperse the gas. For indoor areas, dispersion has

to be done us ing reliable forced ventilation. Ventilation rates to

disperse the gas may need to be above that required for

human comfort. The design of the ventilation system is not

straightforward and the designer is advised to seek

professional advice.

Operation and Maintenance

Whilst the hazards from the use of inert gases can be reduced





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during the design, often they cannot be eliminated. The

remaining hazards must be managed by operating

procedures.

Confined Space Working

Confined spaces are areas which are not usually occupied

and where asphyxiant gas could build-up. A common example

is a vessel which is normally inerted and needs worker access

for maintenance. The best approach is to avoid entry in the

first place – for example, it may be possible to clean vess el or

take samples remotely. Unfortunately, this is not always

possible.

Confined space working is a potentially dangerous activity and

needs to be planned carefully. It is outs ide the scope of this

note. Before planning confined entry, the reader should seek

professional advice.

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