Check the heads

Recent trend of glass bulb sprinklers not having the proper amount of fluid in the bulbs.

These sprinklers have been discovered installed in systems that are “in service” during inspections. Also, some contractors’ field personnel have come across them prior to installation.
As you are well aware, the amount of fluid in the glass bulb plays a critical role in the proper activation of the sprinkler head. The fluid in the glass bulb expands when exposed to heat. When the rated temperature is reached, the fluid expands sufficiently to shatter the glass bulb, allowing the sprinkler to activate and water to flow.
The small air bubble within the glass bulb determines the activating temperature of the sprinkler. As heat expands the liquid, the air bubble is compressed and absorbed. When the bubble disappears the pressure rises rapidly until the bulb shatters. The larger the air bubble the longer it takes before the sprinkler activates.
Please have your personnel carefully inspect all sprinkler heads prior to installation.
Also, please report any occurrence with these sprinklers to our office. If possible, please send the sprinklers to our office.
Thank you for your concern with the correct design and installation of a very important life safety system.  Please know that we are committed to ensuring the highest levels of safety and quality in the systems that are designed and installed in the State of Minnesota.  We are encouraged by your commitment and hope that this information is helpful in that goal.  Please contact us with any questions or comments you may have.