BRE is leading the way with an analysis technique that is new in fire testing
Last March saw the publication of EN 45545, the European standard focusing on the fire protection of railway vehicles. For the railway sector, it comes at an advantageous time as the last few decades have seen significant change within the rail industry. With rail services operating across national borders, especially in Europe, the interoperability of rolling stock has become a priority.
As part of this process, this European fire safety standard is crucial and its provisions will become legal requirements when they are referred to in European Rail Agency (ERA) Technical Standards for Interoperability (TSIs), which also aim to promote a common market for rolling stock within the European Union (EU).
EN 45545:2013 is made up of seven parts covering: fire safety requirements for materials and components, fire barriers, rolling stock design, electrical equipment, fire control and management systems and provisions for flammable liquids/gases.
Part 1 of EN 45545 contains the main terms and definitions, general regulations governing the categorisation of rolling stock in their use and design, and the fire safety criteria.
For testing and certification purposes, rolling stock is classified in four operational categories (see table). Categorisation is based on where the rolling stock is to be used. Vehicles that are not designed or equipped to run in underground sections, tunnels and/or elevated sections are considered to be of lower risk from fire. Vehicles designed or equipped to run in underground sections, tunnels and/or elevated structures but where evacuation times may be unacceptably high are considered higher risk. Two other categories in between these relate to stations that can be reached within a short or long running time.
Rolling stock is also categorised by design (such as sleeping stock or double decked), with the different designs having different hazard levels (HL) according to their operational category. There are three hazard levels.
Hazard Level Classification
Automatic trains having no emergency trained staff on board
Sleeping and couchette vehicles
Part 2 of EN45545 focuses on the requirements for fire behaviour of materials and components.
The performance of materials and components in rolling stock during a fire depends on both the innate properties of those materials components and how they are used. Position, thickness, mass and other factors all have to be taken into account.
Items for testing are placed in certain groups.
- Exterior located
- Electrotechnical equipment
- Mechanical equipment
Each group is subdivided into individual product numbers, to which a specific set of test requirements are allocated. The limit value for each test parameter depends on the vehicle’s hazard level: HL1, HL2 or HL3
Many of the requirements include a smoke and toxicity test in which the analysis of fire effluents is carried out by FTIR (Fourier Transform Infra-Red). The use of FTIR analysis is relatively new to fire testing and is a significant development.
FTIR is commonly used in industry to determine the chemical make-up of compounds. Here it is adopted qualitatively to identify unknown compounds and to determine their structure. Its use in the quantitative analysis of fire gases is more recent.
The gases produced by combustion of a test specimen in a sealed chamber are fed via a heated line – to avoid condensation – to a gas cell which is connected to an FTIR spectrometer. The gases are quantified by analysis of the absorption spectra of an infra-red beam. The system is pre-calibrated using gas cylinders of known concentration.
While previous techniques allowed gas concentrations only to be measured at fixed times, this technique makes it possible to measure continuously throughout the test period.
This is a key advantage of the technique and continuous measurement is likely to be introduced to the standard when it is revised.
Another useful attribute of FTIR fire gas analysis is its ability to detect a wide range of gas species in a single run. Prior to the use of FTIR, toxicity tests would involve a number of different analysis techniques, each specific to a particular gas species. Testing could be slower and more limited in terms of the compounds measured.
For example, a wide range of gases can be generated by a sample. The FTIR system must be calibrated properly with spectra from all the different possible gases analysed and at all concentrations.
It is possible to purchase multiple cylinders, containing a variety of concentrations within the calibration range, but this approach is neither economical nor sustainable. BRE uses a mass flow controller, which allows two cylinders to be connected to it and gases to be mixed together, enabling different levels of concentration.
BRE was involved in the revision of EN 45545 and has been a leading proponent of FTIR testing technology. It participated in the EU’s Transfeu project to improve the fire safety of public transport systems and is therefore well placed to help clients understand the requirements and devise appropriate test programmes. It is providing these services to a range of companies.
Use of FTIR in other areas
BRE has also worked with companies in the maritime sector, which have to meet IMO FTP International Maritime Organisation Fire Test Procedures (IMO FTP) 2012.
And the work will not stop there. As BRE and other companies expand their ability to test for more and more gases at different levels of concentrations, other standard tests will require the use of FTIR for toxicity testing. Initially, this work will probably focus on other areas within the transport sector but wherever it leads, BRE will continue to improve the analysis and push the boundaries of what is possible with FTIR.
If you have an enquiry regarding FTIR please email firstname.lastname@example.org quoting FTIR in the subject line.