Linear Heat Detection Used in Brand New Seattle Tunnel


The brand new State Route 99 double-decker tunnel in Seattle opened on the 4th February 2019. The tunnel, which cost upwards of $3.3 billion is expected to fundamentally change the texture of downtown Seattle, both visually and logistically, and was built as a replacement for the ageing Alaskan Way Viaduct.

The tunnel was deep-bored using a giant boring machine, known as Bertha, famously got stuck for two years and had to be dismantled so they could remove it piece by piece, rather than using the more traditional method of cut-and-cover.

The tunnel is roughly two miles long end-to-end and open to motor vehicles, with no cycle or pedestrian access.

Safety Precautions

Due to the vast length of the tunnel and the high volume of traffic that passes through it, a variety of safety equipment was installed throughout the tunnel  and procedures developed to keep everyone safe in every eventuality:

  • Accidents and Pile-Ups
    In the event of an accident or pile-up, emergency responders will get to the scene on 8-foot hard-shoulders and LED signs will give instructions to other drivers.
  • Emergency Refuge
    The tunnel has 15 emergency refuge areas located every 200m (650 feet), with escape routes that lead to north and south portals. There are also a number of variable message signs and emergency telephones throughout the entire tunnel.
  • Monitoring
    There are over 300 security cameras installed in the tunnel that are continually monitored by a WSDOT traffic control centre.
  • Earthquakes and Floods
    The tunnel is designed to withstand a 9.0 earthquake and stay watertight. In the event of a flood, the tunnel can pump 1,090 gallons of water per minute and has emergency storage below that can hold 480,000 gallons.

Fire Safety

In addition to the safety precautions mentioned above, fire safety is a particularly important consideration.

To keep the tunnel safe from fire, linear heat detection is installed above the road to provide a warning when the air temperature rises faster than 16°C per minute or reaches 88°C. Once a fire alarm is raised, the tunnels extraction and jet fans will jump into action and a sprinkler system will be activated.

Linear Heat Detection

Linear heat detection uses heat sensing cable to detect changes in temperature. Once the cable reaches its predetermined temperature or detects a rapid increase in temperature, a signal is sent to the fire alarm control panel to raise an alert. The exact location of a fire, or excess heat, is also reported, allowing fires to be located and dealt with as quickly as possible.

Linear heat detection can provide quick and reliable detection even in the most challenging of environments. It is not affected by pollution such as exhaust fumes and protective sheaths are available for additional protection from UV, mechanical abrasion, hazardous hydrocarbons such as fuel oils, diesel and kerosene and high temperatures.

All these properties make linear heat detection the ideal detection type for road tunnels.


FyreLine is Eurofyre’s brand of Linear Heat Detection. FyreLine is available in two variations:

FyreLine Digital (fixed heat)

FyreLine Digital offers fixed heat detection at rated temperatures of  68°C, 88°C, 105°C or 185°C. Once the cable reaches its rated temperature, a signal is relayed to the fire alarm control panel.

FyreLine Analogue

FyreLine Analogue continually monitors for changes in temperature. This means that the alarm temperature can be defined by the user. As FyreLine Analogue continually monitors for temperature changes, it can also be programmed to provide a pre-alarm, allowing time for potential fires to be investigated and dealt with before a full alarm is raised.

Either version of FyreLine is well suited for road and rail tunnels.

For more information about the FyreLine Linear Heat Detection system, or to discuss any of the other products that Eurofyre have to offer, please feel free to get in touch either by phone on +44 (0) 1329 835 024, by email to [email protected] or via the online enquiry form situated on our contact page.

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