Is Bacterial Corrosion Destroying Our Infrastructure?
By Dr. Harriet Burge, EMLab P&K's Director of Aerobiology
The recent natural gas explosion in San Bruno California (not far from EMLab P&K's San Bruno
offices) has prompted many questions about the safety of our aging infrastructure. This event
killed seven people, injured many more, and destroyed 37 homes. Another explosion of this kind
occurred in the southwest killing 12 people. At least one possible cause of these explosions is
microbial corrosion of the steel pipes that carry the gas.
It is hard to imagine that something as small as a bacterium can cause such devastation.
However, there is power in numbers, and in the very powerful chemicals that bacteria can make
from minute amounts of nutrients. Here is how it works.
First, where do the organism come from? As we know, bacteria are ubiquitous on earth, and there
are at least some of them on virtually every surface that is not designed to specifically exclude
them. You can imagine that these giant steel pipes are no exception. While attempts are made not
to include large amounts of soil inside the pipes, they cannot be made sterile. Unfortunately,
many of the bacteria that can cause corrosion produce endospores, which are highly resistant
structures that can live for many years. These spores are common in soil, and are likely to be
present throughout the many miles of gas pipeline throughout the world.
Why don't these explosions happen more often? The essential ingredient that is missing is water.
The pipes are designed to exclude soil water, so that, as long as they remain intact, water is
not present. How does water get into the pipes? In a well-designed, well-laid pipe, the water
probably comes from the gas itself. It may also be that 50 years ago (which is when the San
Bruno pipes were laid) the pipes were not as carefully constructed or laid as they are today.
The bacteria that cause metal corrosion are primarily anaerobic forms. When water is present in
an environment with oxygen, a biofilm begins to form. The organisms in the upper layers of the
biofilms use all of the oxygen so that an anaerobic niche is formed, allowing these corroding
bacteria to grow. The most common bacteria that lead to corrosion of steel can use sulfur as an
energy source, and even a small amount of sulfur present in the steel or on surfaces can be
enough. The bacteria use the hydrogen in the water to reduce sulfates, sulfites, thiosulfates,
and sulfur to hydrogen sulfide, which then reacts with metal to form metal sulfides.
Biocorrosion gradually weakens the walls of the pipes, and the high pressure gas (1000lbs/in2)
eventually ruptures the pipe and is released at high speed through the failed metal. The rapidly
escaping gas ignites, leading to a catastrophic explosion.
Of course, there are other causes for gas explosions, and even other microbial corrosion pathways
that can be causative. For all of the microbial problems the solution is to assure that water
does not enter and accumulate anywhere in the pipeline.
This article originally appeared in the November 2010 issue of Indoor Environment Connections.
Reprinted by permission.
About Dr. Harriet Burge
Dr. Harriet Burge is EMlab P&K's Director of Aerobiology and Chair of EMLab P&K's
Scientific Advisory Board. Widely considered the leading expert in indoor air quality (IAQ),
Dr. Burge pioneered the field more than 30 years ago. She has served as a member of three
National Academy of Sciences committees for IAQ, including as Vice-Chair of the Committee
on the Health Effects of Indoor Allergens. View Dr. Burge's Curriculum Vitae.
Read "Ask Dr. Burge" articles