Handling the pressure?

Whether in life science, medical research departments or the analytical laboratory – environments where a dependable supply of high purity nitrogen is crucial – the system of delivery can be a cumbersome procedure; and one that is not without cost penalties and health and safety risks. John Forman looks at the issues

FOCUSING on the purchase price of nitrogen, many science departments and laboratories still rely on gas cylinders or liquid nitrogen as their source. But these sources constitute an on-going array of expenses. When the costs associated with order processing, cylinder rental and handling and delivery are considered, these ‘hidden’ expenses can contribute to escalating overall costs.

Use and storage of any compressed gas under high pressure (up to 250 bar and higher) can be dangerous if proper gas handling procedures are not observed. As a result, an increasing numbers of analytical instrument users choose to use nitrogen from on-site nitrogen generators that operate at a fraction of this pressure and have very low volumes of stored gas within them. It is a decision based on a four major considerations: safety, cost, convenience and purity.

The presence of high pressure gas cylinders in the laboratory has always presented the risk of a cylinder that suddenly depressurises. There is enough force released from a European L-sized cylinder to accelerate it to over 100km/h in approximately ten seconds – enough momentum to cause some severe damage. That is why legislation requires cylinders to be strapped to a wall or floor fixture.

While the above example is extremely unlikely to occur, the biggest health and safety issue in relation to gas cylinders and bottles is the simple manual handling of the items when it comes to replacement and movement. The HSE’s Guidance (issued in June 2004) on the safe use of gas cylinders details the areas that need to be considered when lifting, transporting and storing gas cylinders. These elements – alongside the training which must be delivered to personnel – add a burden to a seemingly simple piece of equipment.

The modern alternative to gas cylinders is a reliable, continuous supply of high purity nitrogen through nitrogen generators designed to operate with a source of clean, dry compressed air.

As well as the cost and safety considerations, it is not unusual for laboratory cylinders to be positioned at some distance from where the gas is used and hence there is a need for long gas supply lines. With longer lines there is the potential for leaks, so there is a requirement to regularly leak-check the gas supply line which increases costs and decreases convenience. Leaks will also allow impurities to enter the gas supply, which reduces purity and influences the accuracy of any analysis. Nitrogen generators are typically placed next to the instrument that they are supplying, thus removing the need for extended gas lines and associated problems affecting purity, cost and convenience.

High-pressure gas cylinders can require regular replacement and can present the inconvenience of running out part-way through an analysis procedure. That means unplanned ‘downtime’ for cylinder replacement and the need to restart an analytical instrument and wait for a stable baseline before samples can be run again.

Because nitrogen generators provide a constant source of gas, the risk of variance in purity is removed, which helps to improve the analysis. Purity is also preserved because there is no chance for impurities to enter the supply pipes, which is a possibility when cylinders are replaced and regulators changed.

The better quality nitrogen generation units are supplied with the necessary pre-filtration already fitted, along with pressure gauges and a flow meter to ensure accurate system monitoring at all times. When laboratory procedures are reliant upon continuous efficient performance from a nitrogen generator, constant surveillance is vital. By properly monitoring a system, unproductive time is decreased, energy can be saved, and output increased throughout. With the NG range’s electronic monitoring panel, all of these benefits are achievable. The control panel, capable of controlling up to three towers, is available on all NG generators and provides an oxygen indicator and alarm, a nitrogen purity indicator, output pressure indication and alarm, and an automatic request for maintenance.

The use of nitrogen within the laboratory is not an element which can be readily replaced. However, the development of nitrogen generation units offers the benefits of: proven technology, simple, reliable and durable; an independent on-site supply of nitrogen; continuous availability; exact nitrogen purity for application demands; low operating costs for extra efficiency; elimination of safety hazards; customised engineering and modularity to meet specific requirements. All of these elements make a powerful argument for abandoning the old, inefficient gas cylinders and embracing this efficient, modern technology.