The effectiveness of ventilation is a regular topic in the CIBSE Air Quality task group, and an important one for those operating trains as well as buildings.
When it comes to ventilation, the rail industry is looking to the built environment sector to optimise comfort for its passengers. This article summarises a ‘knowledge search’ on railway ventilation, and looks at the differences between office and train environments, focusing on standards and practical considerations for managing ventilation.
Train companies work hard to ensure the comfort of their passengers, but the rail industry faces some unique challenges that building service engineers do not encounter.
Comfort
Research shows that reduced ventilation in offices can have a variety of effects on people, including causing headaches and tiredness. In office settings, maintaining indoor air quality is paramount for ensuring occupant comfort and productivity.
In office settings, HVAC systems play a crucial role in maintaining indoor air quality. We found various standards and guidelines on CO2 levels that ensure comfort and productivity. CIBSE recommends keeping CO2 concentrations below 1,000 parts per million (ppm) to ensure a comfortable indoor environment. Similarly, British Standard BS 40102-1:2023 suggests that ‘acceptable’ CO2 levels are between 800 and 1,000ppm.
This is where we have found a challenge for rail.
CO2 levels in rail
The Locomotive and Passenger (LOC & PAS) National Technical Specification Notice (NTSN) includes a standard for CO2 on board trains. It specifies that the ventilation system should maintain a CO2 level not exceeding 5,000ppm. This concentration was chosen to align with the HSE’s workplace exposure limit outlined in EH40/2005. We also looked into other modes of transport, such as aviation, and found that similar standards focusing on workplace exposure are used.
The specified CO2 limit for trains is much higher than people would expect in buildings. In effect, remarkably high CO2 levels are allowed on trains. If concentrations around 5,000ppm were reached, it would be reasonable to expect similar effects on people as those observed in poorly ventilated buildings.
Monitoring CO2 levels onboard trains
Train ventilation requirements differ from those in offices for two key reasons. First, the regular opening of the doors provides a flush of ‘fresh’ air that reduces the CO2 concentration; the more often a train stops at stations, the more likely it is to have a lower concentration. Second, trains can be much busier than offices and CO2 concentrations can rise quickly when lots of people are onboard.
The Rail Safety and Standards Board (RSSB) has monitored CO2 concentrations on trains. One recent project included monitoring CO2 concentrations alongside black carbon and particulate matter for various train classes and journeys. We found that CO2 levels were below 1,000ppm on most trains and routes assessed.
Measured concentrations of CO2 were therefore significantly lower than the limit set out in the LOC & PAS NTSN. This suggests that ventilation systems are operating effectively on the train classes tested.
Ventilation on modern trains
Another factor that the RSSB has investigated is the design of train ventilation systems. Newer trains have numerous features, including ventilation, that are designed to save energy. Fresh air intake is controlled using CO2 sensors so that power demand only increases when more ventilation is needed.
Through discussions with manufacturers and train HVAC suppliers, we have found that the target CO2 levels used in these systems are much lower than the value set out in the NTSN. The target concentrations align more closely with the standards for indoor air quality in buildings.
The RSSB provides guidance to train companies on issues to consider when buying new trains. Our Key Train Requirements document includes lots of useful guidance, including on train ventilation systems, emphasising the importance of controlling the amount of fresh air intake in proportion to passenger loading. This approach helps manage CO2 levels effectively while avoiding unnecessary energy use.
Conclusion
Good ventilation is crucial for ensuring occupant comfort and health, whether in an office or on a train. However, the standards and practical considerations for the two environments differ significantly.
Office environments adhere to stricter CO2 guidelines to promote productivity and wellbeing among building occupants, whereas the rail industry has higher thresholds aligned with occupational standards.
The CIBSE Air Quality task group is a fantastic forum for sharing best practice on indoor air quality. We will continue to learn from other sectors, such as the built environment, to provide guidance to train operators
so that passengers are able to travel in comfort.
About the author
Ben Warren is emissions principal at the Rail Safety and Standards Board and a member of CIBSE’s Air Quality task group
