A question that is frequently asked when considering the installation of a nitrogen gas generator is "will the system create an oxygen rich or oxygen deficient atmosphere that could be potentially hazardous?"
This blog discusses some simple basic key points that need to be addressed to ensure that a Parker nitrogen gas generator
installation is safe to operate and maintain.
The exposure limit for oxygen within the workplace is a minimum of 19.5% and a maximum of 23.5% according to European Industrial Gases Association, (EIGA) and the Occupational Safety and Health Administration, (OSHA). At sea level, oxygen forms 20.9% of the Earth's atmosphere.
A nitrogen generator, typically either membrane or PSA technology, uses compressed air to produce nitrogen gas by removing the constituent atmospheric oxygen content. This could have the potential to alter the ambient levels of oxygen within the installation site or at the point of use in some of the following ways:
- The exhaust or permeate contains oxygen that is vented to atmosphere as part of the normal process to produce nitrogen, possibly increasing the ambient oxygen level.
- Nitrogen could leak from buffer or process vessels and pipe-work within the installation area, possibly reducing the ambient oxygen levels.
- Automatic or manual venting of "off-specification" nitrogen during commissioning or purity control, possibly reducing the ambient oxygen levels.
- Safety pressure relief valves on pressure vessels could vent nitrogen on over-pressure situations, possibly reducing the ambient oxygen levels.
- At point of use, nitrogen could be vented into the workplace as a normal part of the application or process, possibly reducing the ambient oxygen levels.
- Depressurisation by venting nitrogen vessels during servicing or inspection, possibly reducing the ambient oxygen levels.
Although the ambient level of oxygen could be changed and fall outside of the safety limits in each of the scenarios above, in an adequately ventilated environment this normally doesn't occur.
The reason for this and the explanation as to why oxygen and nitrogen do not settle into ambient layers or high/low oxygen gas "pockets" is through a process called "diffusion" created by the random motion of gas molecules.
Oxygen and nitrogen are very similar in density (oxygen is 1.331kg/m3 and nitrogen 1.165kg/m3 @ 20ºC, 1013 millibar absolute), and therefore diffusion is extremely rapid. This phenomenon combined with normal conduction/convection currents and air movement occurring within a building ensures a return to the perfect gas mixture at sea level of 20.9% oxygen / 78% nitrogen.
The really important consideration is adequate ventilation to provide enough fresh ambient air, allowing complete diffusion to rapidly take place and negate any possibility of oxygen concentration or depletion.
"Consideration should be given in building ventilation design to accommodate possible accumulation of product or waste gases. Adequate ventilation shall be provided to prevent localized oxygen-deficient or oxygen-rich atmospheres. As a guideline, the building should have a minimum of six air changes per hour."
— European Industrial Gases Association, (EIGA)
During the design of plant rooms and factories, heating and ventilation systems are normally sized and installed to suit the operational requirements.
Typical room volume change demand per hour data is available from many sources and some values obtained online are detailed below.
| Compressor/boiler rooms
| Manufacturing factories
| Machine shops
During normal operation, a Parker nitrogen generator should not vent any significant volumes of oxygen or nitrogen gas within the installation location as long as the area is adequately sized and ventilated. This obviously depends on quite a few factors including but not limited to - the free volume of room where the system is installed or gas used within, potential exhaust/permeate flow, possible nitrogen vent capacity, and room ambient air volume change rate.
What can be done to mitigate the potential for oxygen depletion or enrichment?
Check pressure vessels, pipe-work, equipment and connections during installation and subsequent service periods to ensure that the system is completely gas-tight.
A common misconception is that the waste gas from a generator is 100% oxygen. This is not the case and in the instance of Parker membrane technology the permeate stream is typically up to 40% O2 and with Parker PSA generators a peak of between 35% to 45% typically occurs at the point of cycle change over. It may be possible to pipe the exhaust gas to an outside open location in certain instances in which case it is important to keep the vent pipe run as large a diameter and as short as possible to prevent any back pressure stopping complete regeneration/sweep of residual oxygen. Obviously, the nearer the equipment is sited to an outside wall, the better.
In certain circumstances, safety pressure relief valves fitted to pressure vessels are required to be piped to an outside location. Threaded outlet port variants are used to make it easier to attach pipe-work to facilitate this. Again, the nearer the vessels are sited to an outside wall or suitable vent location, the better.
Pressure vessel venting during inspection/servicing
Ensure adequate ventilation and set vessel vent flow to ensure no oxygen depletion occurs. Alternatively, fit a suitable flexible hose of the correct pressure rating to the vessel drain connection and vent to a safe location.
Labelling and warning notices
Warning labels must be installed in prominent locations on plant rooms, equipment, vessels and pipe-work to inform personnel of the possible presence of nitrogen gas. This labeling should also be positioned and spaced on all equipment, vessels and pipe-work so that it is visible, readable and clear from all directions that nitrogen gas is present, preventing wrongful connection resulting in possible contamination or potentially harmful/fatal usage of the gas; for example, connection to breathing air systems.
Off-gas bypass vent and point of use venting
Depending on the generator model/point of use application, Parker has the relevant information and formulae to calculate specific requirements available upon request.
Ambient room analysers
If there is any doubt whatsoever as to the oxygen content of a specific location, especially in confined areas or where ventilation criteria is unknown, then a simple but effective solution is to install an ambient room analyser. These work by having a sensor or multiple sensors installed within the area where oxygen depletion or enrichment may occur, connected to an audible/visible alarm indication unit. Generally, there is alarm indication both inside and outside of the area in question so as to prevent entry to the location in the first place or to warn should an out of specification oxygen situation arise while working within the location. There are many suppliers of these type of alarm units and obviously, the manufacturer's instructions should be fully adhered to when installing, operating and maintaining them as they are a critical safety device.
The information contained within this blog post is offered as a guide only to elicit thought and discussion. It is not exhaustive. There are many site conditions that can influence the overall safety of a gas generator installation and it is the responsibility of all parties concerned in the design, selection, installation, commissioning, operation, maintenance and usage of a gas generation system to ensure it is fully compliant with all relevant safety, operational standards and legislation. Each application should be assessed on its own merits. Please use Parker's extensive experience to discuss your specific requirements. We are only too pleased to help!
Parker has extensive experience and knowledge developed over the past 30 years, with tens of thousands of safe, successful nitrogen generator installations operating globally. In reality, a correctly ventilated plant room or factory provides an ideal location for a Parker nitrogen generation system. If there are any concerns or questions, Parker can provide help and advice including mathematical formulae to calculate exactly what is required with regards to a safe installation, even in ISO container or similar, small modular style plant rooms. Please contact email@example.com for further information. For more information on Parker nitrogen generation systems, please visit our website