BS ISO 23431:2021

What is ISO 23431 about?  

ISO 23431 describes methods for determining airspeed and flow direction, CO, NO and NO2 concentrations and visibility in road tunnels using direct-reading instruments.  

ISO 23431 specifically excludes requirements relating to instrument conformance testing. 

Who is ISO 23431 for? 

ISO 23431 on measurement of road tunnel air quality is relevant to: 

•    Manufacturers of airspeed monitors/systems 
•    Tunnel operators 
•    Air quality assessment agencies 
•    Public and private road management authorities 
•    Regulatory bodies 

Why should you use ISO 23431?  

The main goal of air quality monitoring in road tunnels is to ensure the health and safety of tunnel users (including motorists and maintenance employees), as well as effective ventilation system control. ISO 23431 is to provide road tunnel owners and operators with standard methods for checking and calibrating instruments used in road tunnels to continuously monitor airspeed, CO, NO and NO2 concentrations and visibility. It may also be necessary to operate the tunnel ventilation system to: 

•    Reduce CO and NO2 concentrations within the tunnel environment to enable conformance with in-tunnel air quality criteria for various averaging periods 
•    Prevent or reduce portal emissions and resultant environmental impacts 
•    Ensure appropriate visibility for different tunnel operating conditions 
•    Control smoke and improve the self-rescue time and security of tunnel users in emergency situations such as fires 

With ISO 23431, data from these instruments enables tunnel operators to manage the ventilation system in real time or to take emergency measures.