replacing fusible links in life safety systems

Replacing Fusible Links in Life Safety Systems

The National Fire Protection Association reports that in 2017 there were 499,000 structure fires.  72% of these fires occurred in residential occupancies leaving a remaining 139,720 in occupancies other than residential.  While property damage resulting from these fires was in the billions the focus of this article is protection of life safety in commercial and industrial occupancies many of which contain sophisticated smoke mitigation and fire suppression systems in place.  The non-residential structure fires accounted for 782 deaths or one person for every 179 fires.  Every 2 hours and 40 minutes a civilian perishes as a result of a fire incident.  The risk of injury, death, and fire loss remains unchanged and constant where a fire occurs.  These statistics include a 40% increase in fires in places of assembly, 38% increase in educational facilities, 27% increase in Institutional facilities, 13% increase in stores and offices, and a 2% increase in storage facilities inside of a structure1.

You often hear people talk about death and injury as a result of a fire incident.  Too many people assume these tragic events occur in some horrific manner of human life disintegrating as a result of exposures to temperatures that a person just cannot endure.  In the world of media and Hollywood this is known as sensationalism.  What most don’t talk about is that the overwhelming majority of death and injury from fires is a result of smoke inhalation.

The fact is smoke inhalation is the number one cause of death in structure related fires.2   There are studies and reports regarding this fact across the nation, continent, and world.  Smoke kills!   More than the fire itself.  According to a study of death certificates in 1999 smoke inhalation was determined to be the overwhelming leading cause3 and accounts for as high as 80% of all fire-related deaths.4

Despite the #1 cause of death in fires being smoke inhalation, Smoke containment systems such as mechanical fire dampers, smoke vents, fire doors, and other life safety systems designed to contain smoke have a less stringent safety inspection and maintenance requirements than other life safety systems installed including fire alarm systems, commercial cooking fire protection systems, and special hazard systems.  The National Fire Protection Association through a consensus-based program, authors and publishes Fire Codes as well as Nationally recognized standards.  These standards are typically adopted by the code world as the basis for their national, state, and local fire codes and thus are written into the perspective codes.  Some of these standards such as NFPA 13, 17, 17A, 33, 34, & 96 where links are installed in conjunction with fire suppression systems, they are required within the standard to be periodically removed and discarded.  This change-out requirement is in periods identified within the standard of semi-annually or annually “or more frequently” dependent on the application and potential risk of degradation of the fusible link. 

The replacement requirements of fusible links are a direct result by industry to maintain the integrity of the suppression systems after education and understanding of potential risks associated with retaining fusible links in their installed environments indefinitely.  Reports of fire suppression system failures in both fire and non-fire related cases prompted the understanding and knowledge of how these links were impacted by their installed environment and what factors may warrant a change-out program.  Economical impact is considered and based on the relatively low cost of replacement links the importance of maintaining the integrity of the links and support of manufacturer warranties who manufacturer these links far out-weigh risk of failure of a link to operated as designed, tested, and approved.

UL 33 - Table 6.1 Temperature Classifications and Ratings
UL 33 – Table 6.1 Temperature Classifications and Ratings

Current trade organizations in cooperation with damper manufacturers have written documents as Guidelines for the safety and maintenance inspections on smoke and combination fire/smoke dampers and these guidelines use the codes and standards as minimum safety requirements.  Unfortunately, not all standards have caught up with those as listed above and standards associated with fire and smoke dampers, fire doors, and smoke hatches as such as NFPA 80, 90A, 90B, and 105 are not consistent with their counterparts.  In these documents, the requirements for removal exists, however the allowance of placing the link back into these life safety systems after inspection is included.

There are several reasons this does not make good life-safety sense and why these links should follow the same protocols of that of the other standards.  The status of a fusible link’s operational function as approved and listed cannot be reasonably ascertained through a “visual inspection”.

  1. Service providers performing maintenance and inspections are not skilled in understanding what warrants a good link from a bad one simply by performing a visual check of the link.
  2. Fusible links can become damaged upon removal.  Such damage to the metal alloy can be naked to the human eye and only detected upon examination under a micro-scope.
  3. Fusible links installed in these applications typically are those with lower set-point temperatures.  Metal solder & alloy at lower set-point temperatures is softer and more brittle and thus susceptible to physical damage than those with higher set-point temperatures.
  4. No guidelines or instructions for inspection are identified in the standards beyond if the visual inspection reveals that the link “appears damaged” as written in the standards
  5. No guidelines as to appearance are addressed anywhere within the standards
  6. Fusible links (thermal releasing devices) as a component in a fire protection or fire / smoke containment system are always under a load condition.  This load can vary over the life cycle of the product and degrade over time.  Ambient air temperature fluctuations can cause the alloy or solder to change states thus effecting the reliability of the fusible link to operate as intended when called upon.
  7. Links installed in smoke / fire dampers, fire doors, and smoke hatches exposed to fluctuations in ambient air temperatures can cause alloys or solders to crack or partially melt and then reform changing the characteristics and temperature set points and response times of fusible links.
  8. Fusible links not properly stored and maintained can be exposed to environmental changes that impact the link to operate as intended.
  9. Fusible links in the “installed” application (field) may be susceptible to chemical or environmental conditions that impact the ability of the link to operate as intended.
  10. Fusible links are an approved and listed device.  They are tested and approved to UL33, Heat Responsive Links for the Fire Protection Service.  They are warrantied for a period of one year from date of installation.  Links installed in life-safety systems for periods greater than one year no longer are supported by the link manufacturer.

For all these reasons and to ensure the integrity of our life safety systems, fusible links regardless of where they are installed must be inspected, maintained, and replaced on a regular basis.  Standards such as NFPA 80, 90A, 90B, and 105 need to adopt language similar to that of their counterparts NFPA 13, 17, 17A, 33, 34, and 96 with reciprocity to be maintained and communicated amongst them.  National fire codes including The International Building Code, International Mechanical Code, International Fire Code, Uniform Fire Code, and the Life Safety Code need to adopt language similar to the revised standards or continue to reference the standards as amended within their codes.  State legislature needs to be drafted and proposed to include adoption into their state fire codes with enforcement mandated.

In conclusion:

Fire deaths and injures remain constant in the United States, North America, and the world.  Smoke inhalation continues to be the number one cause of all fire related deaths and injuries.  Improvement of our “installed” life safety systems through proper inspection, testing, and maintenance can only help support efforts to prevent catastrophic losses due to smoke and fire propagation.

Lack of expertise and knowledge as it relates to fusible links in the service industry cannot reasonably identify a damaged link vs. that of an operational link

Manufacturer warranties do not support links installed in applications for periods greater than one year.

Many occupancies now offer a “defend in place” response to fire conditions.  Occupancies such as high-rise buildings, healthcare facilities, senior living center, universities, and educational facilities all rely on our life safety systems for this strategy

And only through legislative and code changes with enforcement can we ensure that human lives are reduced from the risk of smoke inhalation, injury, or death due to propagation from the fire zone to other safe zones within an occupancy.

1NFPA “Fire Loss in the United States in 2017
2Source:  National Fire Protection Association
3 Ciottone’s Disaster Medicine (Second Edition), 2016
4 Richard E. WolfeMD

About the Author

James M. Shea is Director of Sales Operations at Nelbud.
Follow Jim on LinkedIn

He has forty-two years working in the fire protection industry and life safety space including manufacturing, sales & marketing, product management, installation, and service. He previously worked on NFPA technical committees for 10, 17, 17A, 33, 34,80,96 & 105.  He is the current International Kitchen Exhaust Cleaning Association Chair for the ANSI Accredited Technical Standard Development Committee publishing consensus ANSI National Standards including the below publications:

ANSI/IKECA C-10 “Standard for the Methodology for Cleaning Commercial Kitchen Exhaust Systems”
ANSI/IKECA I-10 “Standard for the Inspection of Commercial Kitchen Exhaust Systems”
ANSI/IKECA M-10 “Standard for the Maintenance of Commercial Kitchen Exhaust Systems”

Read another article relating to fire protection – Fire Safety in Commercial Kitchens

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2 responses to “Replacing Fusible Links in Life Safety Systems”

  1. Jason G. Avatar

    Thanks for an insightful article, James. Fusible links are often overlooked but critical components to fire safety. The other aspect that I have seen occur is nuisance trips on the hood fire suppression system. And instead of addressing the cause of the nuisance trip (e.g., exhaust airflow too low because the fan is not working properly or a compromised link), the fire suppression contractor comes in and replaces the fusible link with a higher temperature rated link (usually at the restaurant owner’s request). Then when there is a fire, the response time of the link is not quick enough. Due to the low margin operations of restaurants, owner’s will not hesitate to save money. A higher rated fusible link is likely a lower cost than a fan repair and rebalance (or even replacement). I am curious to hear the author’s thoughts on what responsibility the fire suppression contractor has to address the cause of a nuisance fire suppression discharge.

  2. James Shea Avatar

    Great response! Clearly you’ve been involved in the industry to have these insights. Funny in a conversation today during a marketing collaboration with the team, I had to change the way of thinking even within our own group. Fire Suppression systems never have an accidental discharge. I like the reference you used “a nuisance trip” (one where no fire damage or cause is truly understood). Fire systems can go off for a number of reasons and it is incumbent on the service provider to perform proper due diligence to 1. determine cause of activation, 2. insure it will not occur again if in fact it was due to some level of negligence or improper system maintenance.

    Getting slightly off topic for a moment, our friends at UL currently have a proposal in with NFPA 96 which basically requires that fusible links be replaced with the same temperature link that was removed during service. This proposal has mustered the first round of the Technical Committee and is now before us for public comment. Substantiation is to prevent the introduction of higher temperature links to prevent nuisance trips of the fire suppression system. What is not addressed is were the proper steps taken originally to insure the link activation temperature was / is correct and truly met the needs of the design of the ventilation system and the type of operations / equipment within the space.

    Your assessment of why a fire system may trip is on point. It can trip due to the improper storage and handling of the fusible link, repeated exposures to temperatures exceeding the maximum ambient temperature thereby degrading the link over time, lack of temperature studies as required during initial installation as well as every service, improper or lack of ventilation system maintenance, poor cleaning practices, filter removal catching on link lines, etc. The list is long. And of course I left off – Human error. Something a system service technician never wants to own up to.

    So in response to your inquiry it is my opinion that simply increasing the temperature of links to prevent these nuisance trips is inappropriate and may cause unnecessary damage, fire loss, or even injury or death by preventing early detection of an actual fire condition. It is also important to understand that the fire condition does not always include a point of origin visible fire. It could simply be a rise in ambient air temperature caused through changes in cooking operations, or changes in equipment where the ventilation system as originally designed no longer fits the needs of the operation. This rise in ambient air temperatures may create a fire condition where you have fuel loads within the protected zone as well as combustibles outside the protected zone capable of auto ignition. A prime example of this would be where class A materials are used for cooking and creosote collects in the ventilation system. Creosote has a flash point temperature of 165*F (74*C) and an auto ignition temperature of 451*F (233*C). If a fusible link temperature is not adjusted to meet the needs of the application (below these temperatures) and ventilation systems are not designed appropriately to limit the rise in ambient temperature, a fire will most likely occur.

    Unfortunately, fire system service technicians are not trained in air flow, fan maintenance, or ventilation systems.

    They can however follow the requirements of NFPA Standards or manufacturer design manuals by addressing changes in ambient temperature during service (temperature studies) and monitoring any / all changes. Other preventative measures can include addressing changes in the cooking process, or changes in Operations ( 9am to 9pm operations vs. 24/7). If temperature changes are identified and documented during services a debriefing with the owner or operator on these changes can occur with a recommendation in writing for evaluation of the ventilation system. Checking for possible maintenance needs or re-design of the system to fit the needs of the new operational requirements.