Fire Resilience

The importance of having
fire-resilient stormwater and
sewer systems.

Is your infrastructure fire-resilient?

Stormwater and sewer systems are designed primarily to carry water and withstand live loads, so it is not common that we consider the potential that the pipes we depend on may be exposed to fire or extreme heat. However, with moves towards more resilient communities, we need to be mindful of the possible effects that extreme weather events can have on what we build. Let’s dive into what this means for buried drainage pipes and address a few commonly asked questions.

Is fire a legitimate threat on buried infrastructure?

Wildfires can decimate entire neighborhoods and hundreds of acres of forests in a matter of hours, and their effect on pipelines can be just as devastating.

In recent years western states have been at the center of wildfires that have burned countless homes in just days. In the aftermath of these fires, miles of drainage pipes have been compromised. Melted pipes have caused sinkholes, closed roads, and put city residents on notice for possible roadway collapses during heavy rains. It’s clear the effects of wildfire can go much deeper than what we see on the surface.

Sinkhole

Road closure

Water run off/flooding

According to The National Oceanic and Atmospheric Administration (NOAA), in each of the past seven years (2016-2022), the United States has experienced a major wildfire event with damages averaging over 13 billion dollars per event.

NOAA National Centers for Environmental Information (NCEI) U.S. Billion-Dollar Weather and Climate Disasters (2023).

https://www.ncei.noaa.gov/access/billions/summary-stats/US/2016-2022

How would fire affect a drainage pipe?

Most pipes are buried with several feet of earth cover over the top protecting them from direct contact with surface fires. However, every drainage system also has several exposure points that need to be accounted for. Culverts, by definition, will almost certainly have two ends exposed at surface level (so long as they are not permanently submerged). If fire resilience is a priority, these end sections should be designed to withstand contact with flames and high radiant temperatures. Storm sewers are open to the surface at every inlet of the system. These access points potentially put underground systems at risk.

Are wildfires the only concern?

Aside from the obvious wildfires, there are several other avenues that can introduce fire into a drainage system.

Routine ditch burnings

Routine ditch burnings that are common in many communities to manage excessive vegetation introduce fire risk to any culvert or storm sewer that outlets into a ditch.

A simple cigarette butt or firecracker

A simple cigarette butt, firecracker or hot charcoals from tailgating dropped into a storm sewer grate can ignite dry leaves in the bottom of a catch basin and create a chain reaction in storm systems beneath our feet.

Fuel spills

Fuel spilled on a roadway will naturally flow into some type of drainage system. If that fuel ignites, buried pipelines could be compromised.

What effect can fire have on a pipeline?

The most obvious threat to a pipeline from a fire is the potential to ignite the pipe material itself. To address this concern properly, it’s important to understand that there are differences in how different pipe materials respond to exposure to flames. The table below shows concrete compared to alternative materials and the temperatures which induce ignition and melting. Note that concrete is classified as non-combustible material by the National Fire Protection Agency, fulfilling the requirements set by ASTM E136.

For reference, the ignition temperature (or flash point) of wood is around 299 °C. A lit match can reach temperatures up to 427 °C. A fully-formed wildfire can burn at 816 °C or even higher. A low-lying grass fire may be less-intense but can still generate heat over 288 °C. Ignition of pipe material is especially concerning due to the likelihood that the flame will now spread beyond the isolated exposure point and through the entire pipeline. But whether the material is melting or igniting, it’s clear that fire can pose a serious threat to certain pipe materials.

For example, a shopping center in Northridge, CA, used alternative products for its stormwater drain system. When the storm drain system came in contact with fire embers from a major wildfire, the system was not fire-resilient which caused the system to fail.

Even in the absence of ignition, another factor that can impact pipe performance is the radiant heat from the fire which can quickly depreciate the physical attributes of the pipe. Radiant heat flux is a commonly measured variable in fire design. If a bonfire can emit heat to people standing 10ft away, certainly the radiant heat flux from forest fire will heat objects much further away. FEMA notes that forest fires can ignite objects more than 100ft away from the source point. Each pipe material responds to heat differently, but it is well documented that high temperatures can soften alternative materials, while concrete is typically unaffected by short-term exposure to extreme temperatures.

The following figure from the ASCE journal illustrates that concrete sees very little drop in compressive strength for temperatures up to 648 degrees.

What happens when a pipe burns?

If fires cause a culvert or storm sewer to burn, there are a number of issues that can arise. A burnt-out culvert can certainly lead to immediate collapse, causing disruptions on the surface above, but some of the secondary effects may be even more severe. After a culvert or storm sewer is burnt out, it leaves behind a cavern of dirt beneath the ground. Rainfalls that follow a drainage burnout can cause catastrophic damage to entire communities as the water quickly erodes roadways, foundations, and other infrastructure from beneath the ground. This is particularly hazardous following a wildfire since the loss of above-ground vegetation can create additional severe flow conditions more than normal. Roadways that are adversely affected by these washouts and/or collapses may affect critical access roads, making it difficult or nearly impossible for residents to evacuate or for first responders to access the communities directly affected by the fire. The ensuing chaos resulting from a burnt pipeline makes clear the importance of building fire-resilient infrastructure.

In addition to the immediate effects on the community, a burnt pipeline can also introduce toxins into the air and waterways that pollute the environment and may be hazardous to unsuspecting bystanders. The irritating toxic substances that are emitted during burning, combustion, and decomposition can be a public hazard. Run-off water from firefighting may also have corrosive effects.

What are some best practices that can make our drainage systems more fire-resilient?

The solution to these problems is relatively simple: for pipes that may be exposed to flame or high radiant temperatures during their service life, utilize pipe materials that are unaffected by those conditions. From that standpoint, it is only reasonable to avoid the use of alternative materials in those settings. At a minimum, it is recommended that culvert or daylighted storm sewer end sections are comprised of non-flammable materials.

For a fully resilient solution, reinforced concrete pipe (RCP) is the most universally trusted material for drainage pipes in the face of a wide range of natural threats – particularly wildfires. As mentioned previously, concrete is inherently a non-combustible material and can effortlessly handle short-term exposure to flames or extreme temperatures with virtually no risk to the structural integrity of the buried system. Specifying and utilizing RCP on your projects helps build more resilient communities and future-proof our infrastructure.