# Clarification on two distinct groups of synchronized strobes



## BigAbacus (Feb 18, 2021)

NFPA 18.5.5.4.2 states “ Visible notification appliances shall be installed in accordance with Table 18.5.5.4.1(a) or Table 18.5.5.4.1(b) using one of the following: (2) Two groups of visible notification appliances, where visual appliances of each group are synchronize, in the same room or adjacent space within the field of view. This shall include synchronization of strobes operated by separate systems.”

I believe this to be interpreted as the two groups of strobe being out of sync would be the same as two individual strobes being out of sync. As of 1996 the strobe rate was adjusted so that two strobe could not exceed the 5 flashes per second that would potentially cause epileptic seizures. This would hold true for the two distinct groups just as it would for two strobes being out of sync with a max combined flash rate of 4 per second. 

My dilema is in a larger building with two physical addresses. Each address is protected by a dedicated fire alarm system and all notification devices within that address are synchronized. The two systems are networked together for shared function but the two systems are not synchronized together due to differing strobe protocols. When one address is in alarm it only causes a supervisory in the adjacent address and vice versa. The issue arises in common corridors when both systems are in an alarm condition. Each group/ system of notification appliances is synchronized but the two are creating different two strobe patterns.  

Am I wrong to feel that we are compliant in this situation of two groups not synchronized in common corridors  ? I understand the AHJ has the final determination but I believe my interpretation is defendable


----------



## cda (Feb 18, 2021)

Welcome


----------



## cda (Feb 18, 2021)

I would say NO


My thought is any visible strobes are required to synchronize.

Not near the book, will look when I am.


----------



## cda (Feb 18, 2021)

So I take it these are existing systems ???

Or not?


----------



## cda (Feb 18, 2021)

Some others agree if seen they shall synch






						NFPA 72 - rules regarding synchronization of strobes
					

We're doing work in an office building (happens to be a medical office building) and we're re-doing a single suite).  Our strobes in that suite will be synchronized but the strobes outside the suite are on an older system and will not be synchronized.   We're being told that we need to replace...



					www.thebuildingcodeforum.com
				













						Strobe Code Compliance 101: Visible Appliance Requirements
					

Most contractors install strobe lights to comply with the National Fire Alarm and Signaling Code by simply using a combination audible-visible appliance everywhere one or the other is shown on the plans. It should be obvious that if you follow this method of “compliance,” you will either have an...




					www.ecmag.com
				






If two strobes are in any field of view they must flash in synchronization, and any interruption in the clear viewing path will require additional strobes.


----------



## mtlogcabin (Feb 18, 2021)

BigAbacus said:


> The two systems are networked together for shared function but the two systems are not synchronized together due to differing strobe protocols.


You will have to change one of the systems/strobes so they do not have different protocols


----------



## BigAbacus (Feb 18, 2021)

cda said:


> I would say NO
> 
> 
> My thought is any visible strobes are required to synchronize.
> ...


Code states when more than two are in field of view


----------



## BigAbacus (Feb 18, 2021)

mtlogcabin said:


> You will have to change one of the systems/strobes so they do not have different protocols


Easier said than done. One system is 650+ devices and one is 1000+


----------



## BigAbacus (Feb 18, 2021)

cda said:


> Some others agree if seen they shall synch
> 
> 
> 
> ...


Code is “when more than two are in field of view”


----------



## cda (Feb 18, 2021)

BigAbacus said:


> Code is “when more than two are in field of view”




ok am I lost on the question

In a corridor

Strobes in it

From two different systems

You can see both system strobes, in the corridor

The two systems do not synch?

Your question is do they have to???

If these are the facts submitted,

My answer is yes they do.


----------



## cda (Feb 18, 2021)

So other question new or existing????


----------



## BigAbacus (Feb 18, 2021)

cda said:


> So other question new or existing????


One system is new and one system is existing. Two distinct systems protecting different parts of the building. My question references the code reference noting “two groups” do not need to sync. The code allows two strobes to be out of sync but not more than two. The code section I referenced applies that same logic to two “ groups” of strobes. The flash rate of the two groups can not flash at a rate (5-30) that could induce seizures. Strobe are set up to not flash more than 2 times a second.


----------



## cda (Feb 18, 2021)

BigAbacus said:


> One system is new and one system is existing. Two distinct systems protecting different parts of the building. My question references the code reference noting “two groups” do not need to sync. The code allows two strobes to be out of sync but not more than two. The code section I referenced applies that same logic to two “ groups” of strobes. The flash rate of the two groups can not flash at a rate (5-30) that could induce seizures. Strobe are set up to not flash more than 2 times a second.





Code reference out of 72, and year edition,  so I can see how it reads:::::::   The code allows two strobes to be out of sync but not more than two"""

I have not heard it stated that way, and have not been challenged, when I see strobes out of sync, to include only twp.


How many strobes are you talking about in the corridor????????


----------



## cda (Feb 18, 2021)

this is a guru in the industry,,

send him the question.

I have not seen him in a few years. I do know he is good.

Or call him

Art Black, Chief~  art@carmelfire.com




			CONTACT US


----------



## BigAbacus (Feb 18, 2021)

cda said:


> Code reference out of 72, and year edition,  so I can see how it reads:::::::   The code allows two strobes to be out of sync but not more than two"""
> 
> I have not heard it stated that way, and have not been challenged, when I see strobes out of sync, to include only twp.
> 
> ...


Multiple strobes in multiple common corridors. Don’t have my code book handy but 2013 NFPA72 and the section is in my original post


----------



## cda (Feb 18, 2021)

May not be an easy fix since more than one corridor, but put all the strobes in the corridor on the new system, till you hit a location where you do not see the old strobe???

Or do you need all the strobes ???

Or similar, up the candela and remove some??


----------



## BigAbacus (Feb 18, 2021)

cda said:


> May not be an easy fix since more than one corridor, but put all the strobes in the corridor on the new system, till you hit a location where you do not see the old strobe???
> 
> Or do you need all the strobes ???
> 
> Or similar, up the candela and remove some??


Definitely not any easy fix hence why I reached out to the hive mind of the internet. Looking for validation and additional code interpretations that would solidify the case of “ two distinct groups” being acceptable. Thanks for your input


----------



## cda (Feb 18, 2021)

Read page five starting at


Section 8 What About Photosensitive Epilepsy and Strobe Flash Rates?



			https://www.systemsensor.com/en-us/Documents/AV_Appliance_AppGuide_AVAG266.pdf


----------



## cda (Feb 19, 2021)

Commentary ....


----------



## BigAbacus (Feb 19, 2021)

cda said:


> Commentary ....


The handbook description is my reasoning that backs up the argument that two groups can not flash at a rate that would cause any seizure issues. The handbook explanations are not enforceable the same that appendix notes are not but add the hows and whys of a code section.


----------



## BigAbacus (Feb 19, 2021)

cda said:


> Read page five starting at
> 
> 
> Section 8 What About Photosensitive Epilepsy and Strobe Flash Rates?
> ...


section 8 refers to the flash rate of strobes being reduced to accommodate two out of sync devices.


----------



## cda (Feb 19, 2021)

Still do not agree.

Are you going to calculate the flash rate, and put it in writing that it meets NFPA 82?


----------



## cda (Feb 19, 2021)

Give Al a call


----------



## FM William Burns (Feb 22, 2021)

NFPA 72, 2013
18.5.5.4.2
Handbook indicates the purpose of the synchronized requirements are guided by the human eye and its ability to view a flash of light at a 120/135 degree field of vision. The code’s revision in 07 clarified the intent of the multiple detectors two/ groups.

Handbook (18.5.5.4.2) “The flash rate was adjusted so that two appliances (or groups of synchronized appliances) not flashing in unison cannot produce a flash rate that is considered dangerous. If more than two appliances or groups of synchronized appliances can be viewed at the same time, they must be synchronized”.

It has always been my understanding the the code meant that if there are two visible and not synchronized its not compliant OR if there are two groups within the same field of view and both groups of appliances are not synchronized, they are not compliant.

Example - would be your common corridors shared by two separate groups of strobes. One end or half the length by lets say the existing system and the other half length by the new system. Those groups therefore need synchronization.

So my opinion would be the common corridors are non-compliant. I’ve seen this many times in large industrial, storage and healthcare expansions connecting corridors to buildings etc.

I would recommend having your electrical engineer and or fire alarm service provider check availability of ones system expansion of the notification alarm circuit(s) to cover the corridors and possibly separate the common corridor with detection alarm activated self closing doors keeping the corridors synchronized by the applicable system expanded circuits.


----------



## cda (Feb 22, 2021)

Maybe it is whatever makes you feel good???


----------



## BigAbacus (Feb 23, 2021)

FM William Burns said:


> NFPA 72, 2013
> 18.5.5.4.2
> Handbook indicates the purpose of the synchronized requirements are guided by the human eye and its ability to view a flash of light at a 120/135 degree field of vision. The code’s revision in 07 clarified the intent of the multiple detectors two/ groups.
> 
> ...


“The flash rate was adjusted so that two appliances (or groups of synchronized appliances) not flashing in unison cannot produce a flash rate that is considered dangerous. *If more than two appliances or groups of synchronized appliances* can be viewed at the same time, they must be synchronized”.

This is the situation that is in question. “MORE THAN” is the key. Two strobes do not need to sync, just as two distinct groups do not need to sync. The handbook mentions the scenario of a ballroom and a area outside of the ballroom. The ballroom devices must sync and the area outside of the ballroom must sync but they do not necessarily need to sync between the two groups. This is due to the maximum flash rate of each group not being cumulative together to cause an issue of exceeding the 5 flashes per second that could potentially cause seizure.

Erratic strobes is the situation that we have all encountered when a system is improperly installed or lacking is design principles that accommodate are larger multi panel system. This is truly an issue with random flashes in a common space. We have even seen circuits that were stretched beyond their limits and have an almost runway effect. These are both considered non-compliant and not acceptable.

Modifying the systems in question are not really a possibility due to the quantity of devices and sync protocols differing between the two systems. The NFPA 72 code is considered a minimum for compliance meeting all of ADAs requirements that are incorporated. 18.5.5.4.2 states that I have meet the requirements of the code. I have had the issue with only two strobes being out of sync but not two groups. The same code applies.

I was looking for addition case studies or peoples past experiences with the same scenario in other large facilities that were deemed acceptable. I understand that each jurisdiction is slightly different but all follow the NFPA 72 with slight deviations per suppliementals to muddy the waters.

I appreciate everyone’s time to respond and provide input


----------



## cda (Feb 23, 2021)

Will if you have two groups

You will have more than two strobes out of snych

In the end the local ahj is one you have to make happy


----------



## FM William Burns (Feb 23, 2021)

Totally understand the ballroom and lobby outside the ballroom on different flash sequences. That’s the intent of compliance point. Your post suggests your issue is in a “common corridors(s)”. If the corridors are covered by 2 strobes that don’t share the same flash rate or are not synchronized then the visible notification appliances in said corridors are non-compliant. I don’t believe the hang up is the “two” or interpretation of two. If it’s only two in the area or groups and visible by the eye they need to be synchronized.


----------



## cda (Feb 23, 2021)

Regulations, Codes & Standards Q&A: Strobe synchronization - Regulations, Codes & Standards
					






					www.healthcarefacilitiestoday.com


----------



## cda (Feb 23, 2021)

BigAbacus said:


> “The flash rate was adjusted so that two appliances (or groups of synchronized appliances) not flashing in unison cannot produce a flash rate that is considered dangerous. *If more than two appliances or groups of synchronized appliances* can be viewed at the same time, they must be synchronized”.
> 
> This is the situation that is in question. “MORE THAN” is the key. Two strobes do not need to sync, just as two distinct groups do not need to sync. The handbook mentions the scenario of a ballroom and a area outside of the ballroom. The ballroom devices must sync and the area outside of the ballroom must sync but they do not necessarily need to sync between the two groups. This is due to the maximum flash rate of each group not being cumulative together to cause an issue of exceeding the 5 flashes per second that could potentially cause seizure.
> 
> ...



Hummmm

After reading a little I see what you are trying to say 



Normally, the fire alarm strobes rate is 1 HZ (Hertz) which translates to one flash per second, but if a room or hallway has, let’s say, two or three strobe lights within line of sight, they now have the potential of appearing to flash two to three times per second.









						Fire Alarm Strobe Synchronization: Why Is This NFPA Requirement So Important? - PlatinumFire.us
					

If you have ever witnessed a commercial fire alarm inspection and wondered why fire alarm strobe synchronization is so important, then you should take a minute to read this article […]




					platinumfire.us
				




Not into HZ or flash rates

But maybe if you are not exceeding what 72 allows, might work???

Once again convincing the ahj

Maybe a fire protection engineer or a guru from the brand supplier of your equipment might be able to convince the ahj

Have you emailed or called Al?? To see what he says??


----------



## cda (Mar 8, 2021)

BigAbacus said:


> “The flash rate was adjusted so that two appliances (or groups of synchronized appliances) not flashing in unison cannot produce a flash rate that is considered dangerous. *If more than two appliances or groups of synchronized appliances* can be viewed at the same time, they must be synchronized”.
> 
> This is the situation that is in question. “MORE THAN” is the key. Two strobes do not need to sync, just as two distinct groups do not need to sync. The handbook mentions the scenario of a ballroom and a area outside of the ballroom. The ballroom devices must sync and the area outside of the ballroom must sync but they do not necessarily need to sync between the two groups. This is due to the maximum flash rate of each group not being cumulative together to cause an issue of exceeding the 5 flashes per second that could potentially cause seizure.
> 
> ...





any resolution ???


----------

