Detecting unknown and known gases

Gas detection can be simple where a single gas or perhaps two are to be monitored, but in cases of possible contamination detection the requirement is more complex. Antti Heikkilä from Gasmet Technologies looks at how FTIR technology is addressing this issue

Portable FTIR has radically improved the ability to identify unknown gases and easily add new components to the analytical model

If a single gas or perhaps two individual gases are to be monitored and there are no other interfering gases, then gas detection can be simple and, in many cases, low cost. However, the reality for most people is that occupational health risks can arise from a variety of sources, known and unknown, and as a result the choice of monitoring technology is extremely important.

In most applications, it is possible to predict the most likely sources of contamination. For example, the gases of most interest in a hospital operating theatre would be the anaesthetic gases that are routinely employed. However, several of them are likely to be in use and other gases such as solvent vapours may also be present. A further consideration is that new anaesthetic gases may be introduced in the future and this will affect the monitoring needs.

Traditionally, contamination assessments would be undertaken by gas sampling and laboratory analysis or by leaving sorbent tubes at strategic locations for a period of time and then later removing these for laboratory analysis. Both of these methods are flawed in a number of ways.

Gas sampling merely provides a ‘snapshot’ of air quality at a single location at a single moment in time and is therefore unlikely to be truly representative, while sorbent tubes simply provide an average measurement over a period of time, often for a single location. Both of these methods are unable to identify potentially dangerous peaks, and both of them incur a significant delay before results are available.

Portable instruments that are able to provide real-time readings are therefore preferable. However, most portable instruments either measure only a single gas, or are unable to speciate different gases, or detect ‘unknown’ gases, which often causes false positive readings when the air sample contains more than one volatile organic compound (VOC).

The solution

In recent years, the advanced technology that has traditionally been confined to laboratories has become available in portable, battery-powered instruments. This technology is FTIR (Fourier Transform InfraRed), a gas and vapour monitoring technique that is able to measure almost any compound. The development of portable FTIR has radically improved the ability both to identify unknown gases and easily add new components to the analytical model; this is a major advantage because of the inherent risks involved with looking only for known contaminants. In addition, by providing real-time data for multiple compounds simultaneously users are able to survey sites much more effectively, identifying hot spots and monitoring trends.

The development of portable FTIR has radically improved the ability both to identify unknown gases and easily add new components to the analytical model

An FTIR spectrometer obtains infrared spectra by first collecting an ‘interferogram’ of a sample signal with an interferometer, which measures all infrared frequencies simultaneously to produce a spectrum.

Over a number of years, Gasmet has established a library of FTIR reference spectra that now extends to simultaneous quantification of 50 gases or identification of unknowns from a collection of 5,000+ gases. This means that it is possible to re-analyse produced spectra with the instrument’s PC-based software (Calcmet) and thereby identify unknown gases.

While FTIR is able to analyse an enormous number of gases, the technique is not suitable for noble gases, homo-nuclear diatomic gases (e.g. N2, Cl2, H2, F2, etc) or H2S (detection limit too high).

Portable FTIR technology

This technology is now being employed in a wide variety of applications world-wide. For example, the multi-agency incident response teams in the UK are all equipped with portable Gasmet FTIR instruments, providing a rapid response capability to incidents such as chemical spills, fires and explosions. In other applications these instruments are employed for occupational safety in almost any situation in which multiple compounds need to be measured. Gas analysis in hospitals and inside freight containers are examples of the ways in which FTIR can be exploited.

Gas analysis in hospitals

South Devon Healthcare’s Pharmacy Manufacturing Unit (PMU) at Torbay Hospital is using a portable Gasmet FTIR analyser to conduct highly effective and detailed analysis of anaesthetic gases in a variety of hospital locations.

Jamie Hoyle, a PMU Quality Control Specialist, is responsible for operating the analyser. He says: ‘In the past, the hospital employed contractors to check levels of anaesthetic gases, but this provided only a limited amount of information; staff were fitted with sorbent tubes, so the results merely provided an average concentration for one day, for each of the target compounds.

‘The use of sorbent tubes is unable to provide a complete picture of gas levels because the method relies on the collection of air samples over a complete day and provides no detail on staff exposure in specific locations.

The portable FTIR analyser can be configured to provide continuous readings for up to 25 compounds

‘In contrast, the portable FTIR analyser can be configured to provide continuous readings for up to 25 compounds, so that we can either view live readings or leave the analyser to take measurements in a specific location. This means that we are able to evaluate fully every room, identifying hotspots and locating any processes that result in higher concentrations, even if these levels are transitory.’

In addition to the measurement of anaesthetic gases, the flexibility of the DX4030 has meant that it has also been employed in other applications for the measurement of different gases. For example, when a new coating was applied to the floor of a delivery bay, staff complained of solvent smells, so the PMU’s QC department was called in to conduct a survey to check the safety of working conditions. No gases were found to be above workplace exposure limits so it was quickly possible to reassure staff that they were not at risk.

The main advantage of the Gasmet FTIR over the sorbent tube method is that it provides a great deal more information, which enables the identification of peak concentrations and the proactive management of anaesthetic gases. In addition, it also provides an in-house resource that can be deployed for the analysis of almost any gas.

This technology can also be employed as a fixed continuous monitoring system. For example, the Mater Dei Hospital in Malta has installed a fixed Gasmet FTIR to monitor a range of anaesthetic gas levels in 32 locations including operating theatres and recovery rooms. This data is used to raise alarms and help lower staff exposure to anaesthetic gases by changing working practices.

Freight container contamination

Entry to freight containers represents a significant hazard to staff responsible for inspection, stuffing or destuffing because of the large number of airborne chemicals that can be present. Research in Germany and the Netherlands found hazardous levels of gases and vapours in around 20% of all containers and this level of contamination is now accepted as commonplace.

Containers often travel for extended periods and experience a wide range of temperatures. It is therefore not surprising that unsafe levels of gases should accumulate in the confined space of a container. There are two potential sources of hazardous chemicals inside cargo containers; fumigants and chemicals that arise from the goods or packing materials.

Analysing the gases in shipping containers, which could pose a health risk

Peter Broersma from the Netherlands worked with Gasmet to develop a configuration for a portable FTIR instrument (Gasmet DX4030) that would measure the 50 compounds of greatest concern. He says: ‘We are now able to test for all of these gases in around three minutes, which dramatically lowers the time taken for container inspection and greatly increases the number of containers that can be examined every day.

‘A further major advantage of this technology is the minimal amount of calibration and maintenance that is necessary. A new instrument can be delivered pre-configured and factory calibrated and from then on the only calibration required is a quick zero check with nitrogen once or twice per day. As a result, it is not necessary to transport a large number of expensive, bulky calibration bottles.

‘We now use a portable FTIR for all of our container examination work and we have also supplied a number of these units to freight companies that wish to conduct their own testing.’

In summary, traditional techniques for the detection of gaseous contamination have weaknesses that increase levels of risk, whereas the development of FTIR analysers for use ‘in the field’ means that contaminants can be monitored in real-time and risk levels are substantially reduced.