Simplifying gas handling

In terms of the hazards of gas handling most labs get most things correct most of the time, but as the implications of getting it wrong can affect the health of your staff and your business – Air Liquide’s David Hurren thinks that the time is always right for a helpful reminder of best practice

WHEN it comes to selection of gases most operators have a very clear idea of which molecules they need and what their minimum purity requirements are. An understanding of the primary hazards such as flammability or asphyxiation is likely to be well documented in terms of material datasheets. In the main however, if laboratory managers were to take a test on in-depth questions - such as choice of design materials for pressure regulators, which codes of practice determine when pressure regulators should be inspected or replaced or what published guidance there is in terms of safe handling and storage of cylinders, then that information is not always readily available.

In an ideal world you purchase gas from a cylinder or other source at a guaranteed purity level and gas of this purity is fed straight into the instrument. The reality is that at the very least pressure regulation will be required, and in many cases a significant run of distribution pipework is also needed. It is essential to pay close attention to the selection and monitoring of these areas both in terms of quality and maintenance.

To demonstrate this impact, Air Liquide undertook some research on the relationship between pipe work materials and low level reactive gases, in this case low level mixtures of nitric oxide in nitrogen and nitrogen dioxide in nitrogen. These gas mixtures are commonly used for calibrations in air monitoring analysis. The tests looked at the effect on the measured signal to changes in levels of concentration of gases in the zero to 300ppb range. The pipe work used was around 3000mm in length and was 3mm in diameter. A gas flow of 2L/min was used although additional work was completed at higher flows. The materials used included copper, electro-polished stainless steel and aluminium. For nitric oxide all materials we determined to give an acceptable behaviour, i.e. no delay to response of more than 10 minutes. In practice the minimum delay was with the EP stainless steel.  For nitrogen dioxide the problem material was copper with significant off-set to changes in levels, whilst both aluminium and stainless steel were acceptable.

The same care needs to be taken in selection of regulators. Again the materials of construction and dead space in the regulator can be critical. It is assumed that all regulators perform similarly but it is essential to understand materials of construction for “wetted parts” and for critical applications to obtain regulators that have been tested and supplied with a helium leak test certificate. It is essential to take care to make informed choices in selection of materials. Equally critical is the need for the establishment of purging and commissioning procedures for pipe work. Without this care then the analogy can be drawn with lead in water supply. The water leaving a drinking water works can be to the highest specification – but if it passes through dirty or poorly designed pipe work, in particular lead tubing, then by the time it reaches the point of use it could be well outside acceptable standards. The concept that delivering ultra high purity gas into a pipe work system that is not designed and managed to the correct standards, and that everything will be alright at the analytical machine, makes no sense in either economic or practical terms. Also it does not lend itself to repeatability. The key is to use a suitable purity gas and a well-designed and operated system. This includes the use of suitable gas purifiers just before each machine as a final protection. A competent gas supplier should be able to assist you by providing advice on-site to guide you through every step of this approach.

Once a gas supply system is initially specified then the next challenge is to ensure that all aspects comply with current health and safety legislation and codes of practice. A further challenge is to ensure it continues to be operated within those parameters. In fact, when it comes to gas supply there is a wide range of legislation than can have an impact, from pressure system safety regulations, to confined spaces regulations to manual handling requirements.

As far as the UK goes there are some well established codes of practice, that are recognised by the HSE (Health and Safety Executive) but which are probably little known to laboratory managers. These codes are prepared by the BCGA (British Compressed Gas Association) and are designed to provide guidance on the installation and maintenance of liquid and compressed industrial gas facilities. These codes can be viewed somewhat similarly to the Highway Code when it comes to driving. The codes do not comprise the legislation however, they do cover expected practice and all codes are prepared in consultation with the HSE. In addition to the Codes of Practice (CP Numbers) there are also Guidance Notes (GN Numbers) and, as will become clear, two of these are particularly relevant to laboratory operations. A complete list of publications can be found on the BCGA website, www.bcga.co.uk, and publications can be published via this route if needed. It is the responsibility of the laboratory manager to ensure compliance of systems, storage and operating practice on site, not the gas supplier. The one exception is bulk gas storage which is rented from a gas supplier. In this case everything within the Written Scheme of Examination (WSE) for the rental system is the responsibility of the supplier of that system. There will however be a number of obligations on the party using that system which will be defined in the relevant contract.

In considering a gas system the place to start is to look at pressure. Specifically, any systems attached to a pressurised gas supply, should be considered in terms of the legislation and regulations relating to pressure systems. The user of an installed system and the owner of a mobile system should have a WSE in place. This WSE should be drawn up and certified by a competent person.

The BCGA have a number of Codes of Practice in place in relation to pressure systems. In particular these include CP23 “application of the pressure systems safety regulations to industrial and medical pressure systems installed at users premises”, CP34 “application of the pressure equipment regulations to customer sites” and CP4 “industrial gas cylinder manifolds and distribution pipe work/pipelines (excluding acetylene)”.

Of these documents then CP34 is of more relevance to the gas supplier. Installation of gas cylinder manifolds and distribution pipe work is covered by CP4. This document defines good practice for a new installation, including separation distances and risk assessments, materials selection and routing of pipe work. It also provides guidance on pressure systems (in conjunction with CP23) along with recommendations on a regime of weekly checks (by the user) and annual inspections (by a person with appropriate experience and knowledge). Of particular note in CP23 is Appendix 5. This gives guidelines on examination intervals for equipment attached to transportable pressure vessels - i.e. anything attached to a cylinder. The recommendations for regulators occur when the regulator is regarded as the primary pressure protection device for the system. So, if a suitably rated pressure relief valve is attached to the downstream pipe work then it is the process relief valve that should be examined. However where no such device exists, and that will be the majority of laboratory systems, then regulators should be replaced with a new or refurbished unit, or locally replaced with an approved spare parts kit and functionally checked. This does raise the requirement that regulators be tagged from installation to enable inspection dates to be monitored. It is also increasingly common that in-situ refurbishment is not carried out because of the difficulties of being able to demonstrate that the work has been appropriately carried out.

For more specialised gases with flammable, pyrophoric and toxic hazards then CP18 “the safe storage, handling and use of special gases in the micro-electronics and other industries” contains a wealth of useful guidance and advice.

When it comes to storage and handling of cylinders then there are two guidance notes that completely cover all the issues. GN2 “guidance for the storage of gas cylinders in the workplace” does exactly what the title describes. There are recommendations on set up of storage areas, including segregation of gas types, signage requirements, issues and requirements associated with internal stores and advice on emergency procedures. GN3 “safe cylinder handling and the application of the manual handling operations regulations to gas cylinders” defines the duties of both employers and employees, information on hazards, and provides recommendations on assessments and training.

In all of these cases, it is all very well to be aware of the regulations and best practise, but the critical item is to ensure that the personnel daily dealing with these matters are competent, and that appropriate management systems are in place. In particular it is important that you can demonstrate the capabilities of employees at a given point in time. This is where suitable training can play a part. By use of the correct type of modules it is possible to not only raise employee awareness of safety issues, but provide education on cylinder movement and connection of equipment and to provide demonstrable records of achievement levels. This can be extended if required to provide a safety passport scheme for laboratory staff in relation to gases.

To understand all aspects relating to this topic requires a wealth of expertise. In selecting a gas supply the critical decisions are not about the headline molecules but in consideration of key impurities, validation of supply quality, selection of materials and installation and ongoing maintenance, inspection and training.  The answer is to take the time to select a partner who can deliver on all aspects of this package and can work with you to deliver the benefits of continued repeatability of results and safe and reliable operation. A good partner will assist with the management of these aspects of your business and simplify gas handling.

David Hurren
David graduated from Imperial College in Chemical Engineering.  For most of his career he has worked in the Industrial Gas industry, and for the last 9 years with Air Liquide.