Fire Protection

Microbiologically-related problems—including biofouling (slimes), deposition, and microbiologically influenced corrosion (MIC)—can occur in most water-based fire protection sprinkler systems (FPS).  These problems often compromise the function and integrity of system components by reducing or interfering with water flows, increasing friction factors, and causing component failures due to blockages or leaks.  In some cases, new FPS have failed only three to six months after installation.  MIC can affect all types of FPS (wet, dry, preaction, and antifreeze) as well as undergrounds and storage tanks.

Why FPS Experience Microbiologically-Related Problems
MIC occurs in FPS primarily because MIC-related microbes—including aerobes, slime formers, iron-related bacteria, anaerobes, organic acid-producing bacteria, and sulfate-reducing bacteria (which produce corrosive sulfides and consume hydrogen)—are usually present in supply waters to the FPS.  In addition, nutrients and chemical factors suitable for the growth of MIC-related bacteria are also present in these waters.

It is important to note that water treatments used by water companies to kill pathogenic bacteria are rarely strong enough to kill MIC-related bacteria.    

Microbiologically-Related Problems Experienced in FPS
FPS may experience a variety of microbially-related problems.  Many times, these problems occur simultaneously in an affected system and may not affect all systems uniformly, due to differences in environmental, operational, chemical, and biological factors.  These microbial problems include:


1.   Biofouling of system waters due to biofilms.

  • Biofilms (also called slimes), which are formed by microbial communities—in most cases composed of many different types of microbes (e.g., aerobic, slime-forming, anaerobic, acid-producing, iron- and manganese-depositing bacteria, molds and sulfate-reducing bacteria)—attach to surfaces in contact with non-treated or inadequately treated waters.  Biofilms are an early indicator of microbial activity.

2.   Reduced water flow rates and increased friction numbers due to deposition.

  • Over time, biofilms grow in thickness and areal extent due to microbes depositing iron and manganese and accumulating corrosive materials such as chlorides.  Biofilms mature by collecting more types of microbes (and, therefore, more biochemical reactions) and non-biological materials (e.g., sand, debris, organic and inorganic materials) and form deposits.  Discrete deposits are a clear indication of microbial activity.

3.   Loss of integrity in system components due to under-deposit pitting-type corrosion.

  • Once deposits are established, and given the right environmental conditions, microbial metabolic by-products—such as organic and inorganic acids, hydrogen, carbon dioxide, sulfides, and ammonia—accumulate within the deposits due to the activities of microbes and other chemical reactions.  These metabolic by-products corrode the underlying metal and often lead to rapid under-deposit pitting-type corrosion beneath the deposits.  This type of corrosion is a telltale sign of MIC.  Microbes can both initiate corrosion and accelerate existing corrosion.

4.   Component failures due to under-deposit leaks.

  • Once corrosion and MIC advance to the stage of under-deposit pitting corrosion, the metabolic by-products in deposits corrode the underlying metal until leaks develop under the deposits.  Pinhole leaks are another telltale sign of MIC.

5.   Damage to coatings and destruction of underlying metal due to microbial activities.

  • Microbes enter holidays in protective coatings in pipes and storage facilities.  Once established, microbial production and accumulation of corrosive materials under the coating (and next to the metal surface) causes further disbonding of the coating, allowing damage to the coating and underlying metal to spread and proceed at very rapid rates.  The disbondment acts to trap and concentrate microbes and corrosive materials next to the metal surface, causing even faster corrosion to occur.  Since this occurs under the coating, the site is not protected by cathodic protection and cannot be treated using corrosion inhibitors and biocides.  These problems can occur on the inside or outside of equipment.

Materials Affected
Most metals and alloys, except titanium, are rapidly attacked by MIC under some conditions in FPS.  Common materials employed in FPS that are most susceptible include:  steel, black iron, galvanized steel, stainless steel, and copper.  While susceptible to MIC-type deposits, ductile iron and cast irons rarely experience severe pitting due to MIC. 

Thousands of cases of MIC in FPS have been reported and investigated—many by BTI Products and its sister company, BTI.  Cases of severe MIC have occurred in all geographic regions of the Americas and have involved many types of water chemistries and large numbers of different microbial species (although slime formers, aerobes, anaerobes, acid-producing bacteria, and sometimes sulfate-reducing bacteria groups are usually involved).  Many cases of MIC in potable water and FPS in homes, office buildings, and commercial facilities have resulted in pinhole leaks within months of construction.   Most of the severe pitting in stainless steels is seen in circumferential welds and heat-affected zones, although we have seen a few cases where whole pieces of stainless steel were affected.

Systems Affected
The following FPS systems are all potentially susceptible to biofouling, deposition, and MIC: 

  • All types of FPS (wet, dry, preaction, and antifreeze)
  • All pipes and some sprinkler heads
  • Undergrounds
  • Storage tanks (including water and fuel tanks)

Whether this “MIC potential” progresses to rapid and severe MIC-type corrosion depends on local conditions—even in the same “system”—over time.

Locations in FPS Where MIC is Likely to Occur
Rapid biofouling (slime formation), deposition, and under-deposit corrosion (MIC) begins to occur almost immediately where bare metals are exposed to waters containing MIC-related microbes, adequate nutrients for microbes, and oxygen.  The types of waters containing these “MIC factors” include most potable waters from municipalities, wells, ponds, etc. used in FPS. 

More frequent exposure to MIC factors increases the likelihood of severe MIC.  In wet FPS, the areas which typically suffer from severe and rapid MIC are larger diameter, horizontal pipes that see frequent water flow (and, thereby, new water, MIC-related microbes, nutrients, and oxygen) and accumulate sediments (such as mains and cross mains) and in pipes with trapped air pockets (such as peaked areas).  In dry/preaction FPS, severe and rapid MIC is most often seen in horizontal pipes which are likely to accumulate moisture and/or water puddles and sediments (such as low points and areas adjacent to grooves and fittings).

In those areas where water sits stagnant for long periods—such as dead legs in wet FPS that don’t see much water flow during flow tests—microbes, deposition, and corrosion processes slow down due to a lack of nutrients (most importantly oxygen) and eventually almost stop.

Diagnostic Products for FPS Industry Systems
BTI Products offers test kits designed specifically for diagnosis of microbial problems in FPS.  Our test kits provide microbiological, chemical, and site-specific information important in diagnosis of microbial and other problems and in the design of treatment and prevention strategies.  BTI Products and its many global FPS clients (several thousand since 1995) use BTI Products test kits to investigate MIC and design effective treatment programs.

BTI Products kits can be used for all types of samples—including those containing water, particulates, corrosion products, and/or other materials.  BTI Products test kits are designed to test for MIC-related microbes in virtually any real-world sample—even those containing anti-freeze, treatment and other chemicals and, most importantly, can be used by untrained industry personnel, on-site, to obtain accurate and pertinent data quickly and inexpensively.1

Recommended Diagnostic Test Kits

  • MICkit® FPS for initial testing of FPS for microbes and chemical parameters involved in MIC
  • MIPkit™ FPS to economically test FPS for the most common microbes and chemical parameters involved in MIC
  • MICkit® Pipe Inspection Kit to physically inspect pipes in systems that have tested positive for MIC-related bacteria and/or systems with a history of leaks/failures
  • MICkit® Custom created specifically to suit your testing needs

Diagnostic & Mitigation Services for FPS Industry Systems
BTI Products can also assist in evaluation of samples, test data, field-site investigations, and design and implementation of mitigation measures.  BTI Products performs and supports research and testing programs related to causes, prevention, and treatment of microbial problems for individual clients.

Please contact us to discuss your specific needs.



  1. Scott, P.J.B. and M. Davies. 1992. Survey of field kits for sulfate reducing bacteria.  Materials Performance, May, 64­-67. 


Further Reading
For more detailed information on MIC in FPS, please refer to the following publications:

  • Bioindustrial Technologies, Inc., Practical Guide to Diagnosis and Mitigation of Microbiologically Influenced Corrosion (MIC) in Fire Protection Systems. Colorado: Bioindustrial Technologies, Inc., 2005.
  • Bioindustrial Technologies, Inc., Practical Guide to Diagnosis, Treatment, and Prevention of Microbiologically Influenced Corrosion in Fire Protection Systems, Second Edition. Colorado: Bioindustrial Technologies, Inc., 2001.
  • Pope, D.H. and Pope, R.M. “Microbiologically Influenced Corrosion in Fire Protection Sprinkler Systems.” In NACE Manual on Microbially Influenced Corrosion. Edited by John G. Stoecker II. Houston, TX: National Association of Corrosion Engineers International, 2001.
  • Pope, D.H., and Pope, R.M. “Microbiologically Influenced Corrosion (MIC).” Fire Protection Contractor 21, no. 9 (1998): 24—26.
  • Pope, D. H. “Testing For and Treating MIC.” Sprinkler Age 18, no. 12 (1997): 22.