Why Sprinkler/Heat Detector Temperatures?

1/4/2023

Looking for some back history here - why is heat sensor detection temperature 57 degrees C?

On what basis was sprinkler temperature determined to be 68 degrees C?

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10 Comments

Alex

1/4/2023 06:02:52 am

Complete assumption here, but I would assume it is based on testing/calculations between the RTI of a sprinkler and the thermal lag of a heat detector.

In addition, one is simply a notification device so having an earlier response is beneficial.

Curious to see what others have to say.

Alex

Dan Wilder

1/4/2023 07:45:40 am

For the sprinkler side of things:

As the early patents only show "...a solder connection..." detail/description, my bet is the readily available solder at the time at a lower temperature (to avoid the damage to the building per intent) was or became the standard temp.. This would be a good one to ask NFPA.

https://patents.google.com/patent/US154076
https://patents.google.com/patent/US248828

https://www.nfpa.org/About-NFPA/NFPA-overview/History-of-NFPA

As for the detector side of things, Alex got it with the thermal lag....the (basic) heat detector works with an inherent lag based on the surrounding air temp, currents, and internal operation limitations that need to activate prior to a sprinkler discharge (or it risks not activating at all)

https://en.wikipedia.org/wiki/Heat_detector

Nice little history break this morning, thanks!

Anthony

1/4/2023 08:20:03 am

This.

Code follows technology, the older link style heads operated at a temperature so that's the temperature things were coded for.

Generally, it's helpful to remember that codes are just words written by humans with all the fallibility that is inherent to the condition.

Todd E Wyatt

1/4/2023 08:39:19 am

2022 NFPA 13 Standard for the Installation of Sprinkler Systems includes the following references to “68 degree C” temperature-rated sprinklers :

20.17 * Protection of Idle Pallets.
A.20.17
Idle pallet storage introduces a severe fire condition. Stacking idle pallets in piles is the best arrangement of combustibles to promote rapid spread of fire, heat release, and complete combustion. After pallets are used for a short time in warehouses, they dry out and edges become frayed and splintered. In this condition, they are subject to easy ignition from a small ignition source. Again, high piling increases considerably both the challenge to sprinklers and the probability of involving a large number of pallets when fire occurs. Therefore, it is preferable to store pallets outdoors where possible.

A fire in stacks of idle plastic or wood pallets is one of the greatest challenges to sprinklers. The undersides of the pallets create a shadow area on which a fire can grow and expand to other dry or partially wet areas. This process of jumping to other dry, closely located, parallel, combustible surfaces continues until the fire bursts through the top of the stack. Once this happens, very little water is able to reach the base of the fire. The only practical method of stopping a fire in a large concentration of pallets with ceiling sprinklers is by means of prewetting. In high stacks, this cannot be done without abnormally high water supplies. The storage of empty wood pallets should not be permitted in an unsprinklered warehouse containing other storage.

A series of seven large-scale fire tests involving idle wood pallets stored on the floor was conducted at Underwriters Laboratories in 2009 and 2010. This testing was conducted to investigate the performance of an upright sprinkler having a nominal K-factor of 11.2 (160) when installed to protect a 8 ft (2.4 m) high array of new 4-way entry, softwood pallets under a 30 ft (9.1 m) ceiling. The pallets used for this test series were supplied by CHEP USA. The impact of the sprinkler temperature rating on fire control performance was the key variable investigated during this test series. Except for the temperature rating of the sprinkler’s heat responsive element, the same sprinkler design was used for all seven tests. Three tests were conducted using 286°F (141°C) temperature-rated sprinklers, two tests were conducted using 200°F (93°C) temperature-rated sprinklers, and two tests conducted using 155°F (68°C) temperature-rated sprinklers. The ignition location for all tests was centered between four sprinklers. To enhance test repeatability, the four sprinklers nearest the ignition location were arranged to discharge water when the first sprinkler operated. The results of this test series are summarized in Table A.20.17.

The results of this large-scale fire test series indicated that sprinklers in the 155°F (68°C) and 200°F (93°C) temperature ratings performed significantly better than the 286°F (141°C) temperature-rated sprinklers as evidenced by a reduced number of operated sprinklers and lower steel temperatures.

Table A.20.17 Summary of Fire Test Data for Idle Pallets (4-Way Entry Softwood) Stored on Floor

This does not explain the WHY in your question, sorry.

I could not locate a related reference in 2022 NFPA 13 for “57 degrees C”.

Franck

1/4/2023 09:20:49 am

57 degrees C is for heat fire detection devices, not sprinklers. This is why you won't find it in NFPA 13.

Todd E Wyatt

1/5/2023 08:45:08 am

NFPA 204 references 68 degrees C (see 9.2.5.4.3.2) but it does not reference 57 degrees C.
The referenced NFPA 72 includes multiple references to 57 degrees C … see below.

2021 NFPA 204 Standard for Smoke and Heat Venting
Chapter 9 — Sizing Vents
9.2 Hand Calculations.
9.2.5 Required Vent Area and Inlet Area.
9.2.5.4 Detection and Activation.
9.2.5.4.2.1*
Detection times for heat detectors or fusible links shall be determined in accordance with NFPA 72.
9.2.5.4.3.1*
The temperature rise for activation shall be based on dedicated tests, or the equivalent, for the combustibles associated with the occupancy and the detector model to be installed.
9.2.5.4.3.2
Where the data described in 9.2.5.4.3.1 are not available, a minimum temperature rise of 20°C (68°F) shall be used.

A.9.2.5.4.2.1
The response data in NFPA 72 assume extensive, flat, horizontal ceilings.
This assumption might appear optimistic for installations involving beamed ceilings. However, any delay in operation due to beams is at least partially offset by the opposite effects of the following:
(1) Heat banking up under the ceiling because of draft curtains or walls
(2) The nearest vent or detector usually being closer to the fire than the assumed, greatest possible distance
Fusible links are commonly used as actuators for mechanically opened heat and smoke vents. Where the response time index (RTI) and fusing temperature of a fusible link are known, and assuming that the link is submerged in the ceiling jet, the relationships described in NFPA 72 for heat-actuated alarm devices can be used to estimate the opening of a mechanical vent.

A.9.2.5.4.3.1
This requirement does not have a parallel in NFPA 72. Temperature rise for activation of smoke detectors depends on the specific detector as well as the material undergoing combustion. Limited data on temperature rise at detection have previously been recorded in the range of 2°C to 42°C, depending on the detector/material combination (Heskestad and Delichatsios, 1977).

2022 NFPA 72 National Fire Alarm and Signaling Code
Annex A — Explanatory Material
A.21.5
The continuous monitoring of smoke and temperature is to allow the responding fire fighters to know when the tenability conditions at the floor elevator lobbies are changing. This can be accomplished at a minimum by monitoring elevator lobbies, machine rooms, control rooms, machinery spaces, or control spaces smoke detector(s) for the presence of smoke and a minimum of three ranges of temperature in the elevator lobbies, machine rooms, machinery spaces, or control rooms that provide full bodily access for fire fighters, as follows:
(1) Normal ≤90°F (32°C)
(2) Monitoring (supervisory) between 90°F (32°C) and 135°F (57°C)
(3) Unsafe (alarm) above 135°F (57°C)

Annex B — Engineering Guide for Automatic Fire Detector Spacing
This annex is not a part of the requirements of this NFPA document but is included for informational purposes only.
Users of Annex B should refer back to the text of NFPA 72 to familiarize themselves with the limitations of the design methods summarized herein.
Section B.2, and particularly B.2.2 and B.2.3, are largely based on the work of Custer and Meacham as found in “Performance-Based Fire Safety Engineering: An Introduction of Basic Concepts” (Meacham and Custer 1995) and Introduction to Performance-Based Fire Safety (Custer and Meacham 1997). [25]
The National Fire Protection Association and the Technical Committee on Initiating Devices for Fire Alarm Systems gratefully acknowledge the technical contributions of the Society of Fire Protection Engineers, Richard Custer, and Brian Meacham to performance-based design and this annex.
Table B.3.2.5 Time Constants (τ0) for Any Listed Heat Detector [at a reference velocity of 1.5 m/sec (5 ft/sec)]

B.3.3.7.1
Fixed-temperature heat detectors have been selected for installation in the warehouse with a 57°C (135°F) operating temperature and a UL-listed spacing of 9.1 m (30 ft).

B.3.3.8.1
After 146 seconds, when the fire has grown to 1000 kW (948 Btu/sec) and at a radial distance of 3.3 m (10.8 ft) from the center of the fire, the detector temperature is calculated to be 57°C (135°F). This is the detector actuation temperature. If the calculated temperature of the detector were higher than the actuation temperature, the radial distance could be increased. The calculation would then be repeated until the calculated detector temperature is approximately equal to the actuation temperature.

B.3.3.8.3.5
Using a radial distance of 6.5 m (21 ft) from the axis of this fire, the temperature of the detector is calculated to be 41°C (106°F) after 3 minutes of exposure. The detector actuation temperature is 57°C (135°F). Thus, the detector response time is more than the estimated 3 minutes. If the calculated temperature were more than the actuation temperature

Franck

1/4/2023 09:26:26 am

Sometimes, the answer is... Why not ?
Or based on current possibilities.

Sprinkler temperatures need normally to be set at least 30°C (50°F) above the expected ambiant level within the room for reliability (and avoid spurious activation). As ambiant termperature in a normal industrial plant may be up to 40°C below a steel deck during summertime, 68°C seems more appropriate than 57°C.
In addition, a spurious activation of a heat detector (unless comined with a deluge system) has less consequences than a spurious activation of a sprinkler.

And at the end, former sprinklers had no frangible bulbs but fusible elements. It might have been easier at that time to find the right mix of metal element to reach 68°C, rather than 57°C. But this is just an assumption.

Pete H

1/4/2023 11:32:30 am

I'm pretty sure it's based in having temperatures high enough to prevent false trips/releases, and then what matches the mechanism that allows the release of water (for sprinklers) or sets off the detection (for heat detectors) such as fusible links or glass bulbs.

James E. Art, Fire Protection Engineer

1/4/2023 12:54:37 pm

Standard Accepted Practice
A Lot of the standard practices are codifications of what were accepted as good practices, but may be just acceptance of assumptions.

I recall a story of when a group of early sprinkler manufacturers got together to specify how quickly a fire sprinkler should react to be "acceptable".

They "decided" then that no sprinkler should be slower than the slowest of the bunch at the meeting!

It is good that heat detectors, if installed at recommended spacing, etc are faster than standard fire sprinklers.
May not a apply to Quick Response, Residential, or ESFR.

Dave L.

1/4/2023 01:09:11 pm

Following up on Mr. Wilder, for fire sprinklers, since the earliest development of solder-type sprinklers, a sprinkler temperature of around 160°F (71°C) was deemed safe from accidentally fusing or softening as long as room or ceiling temperature did not exceed 100°F (38°C).
One of the best sources on the history of sprinkler development is “Automatic Sprinkler Protection by Gorham Dana, which is readily available in reprint and electronic format. The version I have is from 1914. Dana based it on a series of lectures he gave before the Insurance Library Association of Boston in 1913. He was the ultimate sprinkler geek! The book goes into the chaotic early years of sprinkler development, including perforated pipe systems from the 1850’s, to releasing devices such as burning cord, gunpowder(!), volatile liquid, or expansion of wax. Then the development of solder, and various release mechanisms, to overcome issues such as water pressure and the heat-sink effect of water in the piping touching the solder. Dana explains that by 1855 innovation settled down to sprinkler designs that we would recognize today, and that the first comprehensive sprinkler testing was in 1884. The composition of low-fusing solder had become more or less standardized, and Barnabas Wood of Nashville took out a patent in 1860 for solder composition consisting on bismuth, Lead, cadmuim, and tin, that had a melting point of 165°F (74°C). Solder from other manufacturers were also in the range, General Fire Extinguisher Company adopted the universal 212°F / 286°F / 360°F categories for instanced where room or ceiling temperatures may be higher. It is fascinating what little has changed in over 100 years!

Why Sprinkler/Heat Detector Temperatures?

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