Re: [PSES] fire safety test methods for different country standards

[Richard Nute]

  

 

Hmm.  Thanks to Ted Eckert, the small tablet may have been methenamine.

 

 

Rich

 

 


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Re: [PSES] fire safety test methods for different country standards

[Richard Nute]

 

Thanks, Brian.

 

I recall now.  I used hexamine tablets.  I used two sizes, one about ½ inch 
diameter and ¼ inch thick, and the other about the size of an aspirin tablet.  
I placed the hexamine on top of the component I expected to catch fire, ignite 
the pellet, put the enclosure back on, and film the results.  

 

We were using HB enclosure material for a product using an external power 
supply (limited-power, low-voltage).  The standards say this construction is 
acceptable.  Nevertheless, a component could overheat and burst into flames.  
So, we tested for spread of fire through the use of the hexamine tablet.  

 

Where the tablet caused the HB enclosure to burn, we used NOMEX sheet 
insulating paper to prevent the flames from touching the HB plastic.  

 

 

Rich

 

 

 

 


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Re: [PSES] fire safety test methods for different country standards

[Ted Eckert]

The fuel used now is a methenamine tablet. The following is one example, but I 
am not specifically recommending them as a supplier. I am only using them as a 
reference.
http://www.ergonomicsusa.com/product/methenamine-tablet-for-timed-burning/

These are a mixture of 1,3,5-trioxane and hexamethylenetetramine. As such, they 
are either the trioxane tablets Mr. O’Connell references or a more modern 
replacement. These tablets are commonly used for flammability testing of 
fabrics, rugs and textiles.

Ted Eckert
Microsoft Corporation
The opinions expressed are my own and do not necessarily reflect those of my 
employer.

From: Brian O'Connell [mailto:oconne...@tamuracorp.com]
Sent: Saturday, May 21, 2016 3:51 PM
To: EMC-PSTC@LISTSERV.IEEE.ORG
Subject: Re: [PSES] fire safety test methods for different country standards

Rich,

Congratulations on your IEEE Fellow appointment. Do we address you as ‘Sir 
Richard’ ?

The tablet was probably trioxane solid fuel; typically in a tablet or bar 
from-factor. See Mil-F-10805. In addition to being used for heating C-rats and 
MREs, were also used for gas mask training by igniting several bars in sealed 
chamber, then marching the troops in to subsequently remove their masks to sing 
our ‘tribal song’.

Brian

From: Richard Nute [mailto:ri...@ieee.org]
Sent: Saturday, May 21, 2016 10:32 AM
To: EMC-PSTC@LISTSERV.IEEE.ORG
Subject: Re: [PSES] fire safety test methods for different country standards

Hi John:

Thanks for your comments.

In the end, the “solution” was a different sort of pragmatic approach because 
the boards were always enclosed in hermetically sealed high pressure (10,000 
psi+) / temperature (180C+) -resistant stainless steel tubes which have very 
little free air volume inside them.

That means that there is very little free oxygen for component fires to use, 
and calculations proved that ignitions involving all the flammable material 
within the enclosures would exhaust that oxygen well before fires could 
develop, and also the way the enclosures are built and sealed means that flames 
or flammable material could not escape unless there had first also been very 
substantial external physical damage.

This is another option.  Build a fire inside the equipment and see what 
happens.  I use a fire-starting tablet or pellet (I’ve forgotten the name).  An 
enclosure with minimum openings that would allow replenishment of oxygen will 
suffocate the fire once the internal oxygen is used up by the fire.  The 
enclosure does not need to be sealed.  Usually, such construction will not have 
very much empty space and therefore relatively little initial oxygen to feed 
the fire.  (I used such testing to prove that a circuit fire would not ignite 
an HB enclosure.)

This is another situation where one can show that a fire will not spread very 
far beyond the initial fuel.

Whether or not this is accepted as compliance with the standard will depend on 
the certification engineer and the policies of the certification house (and 
your ability to convince them that the construction is adequate).


Rich
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Re: [PSES] fire safety test methods for different country standards

[Brian O'Connell]

Rich,

Congratulations on your IEEE Fellow appointment. Do we address you as ‘Sir 
Richard’ ?

The tablet was probably trioxane solid fuel; typically in a tablet or bar 
from-factor. See Mil-F-10805. In addition to being used for heating C-rats and 
MREs, were also used for gas mask training by igniting several bars in sealed 
chamber, then marching the troops in to subsequently remove their masks to sing 
our ‘tribal song’.

Brian

From: Richard Nute [mailto:ri...@ieee.org]
Sent: Saturday, May 21, 2016 10:32 AM
To: EMC-PSTC@LISTSERV.IEEE.ORG
Subject: Re: [PSES] fire safety test methods for different country standards

Hi John:

Thanks for your comments.

In the end, the “solution” was a different sort of pragmatic approach because 
the boards were always enclosed in hermetically sealed high pressure (10,000 
psi+) / temperature (180C+) -resistant stainless steel tubes which have very 
little free air volume inside them.

That means that there is very little free oxygen for component fires to use, 
and calculations proved that ignitions involving all the flammable material 
within the enclosures would exhaust that oxygen well before fires could 
develop, and also the way the enclosures are built and sealed means that flames 
or flammable material could not escape unless there had first also been very 
substantial external physical damage.

This is another option.  Build a fire inside the equipment and see what 
happens.  I use a fire-starting tablet or pellet (I’ve forgotten the name).  An 
enclosure with minimum openings that would allow replenishment of oxygen will 
suffocate the fire once the internal oxygen is used up by the fire.  The 
enclosure does not need to be sealed.  Usually, such construction will not have 
very much empty space and therefore relatively little initial oxygen to feed 
the fire.  (I used such testing to prove that a circuit fire would not ignite 
an HB enclosure.)

This is another situation where one can show that a fire will not spread very 
far beyond the initial fuel.

Whether or not this is accepted as compliance with the standard will depend on 
the certification engineer and the policies of the certification house (and 
your ability to convince them that the construction is adequate).


Rich

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Re: [PSES] fire safety test methods for different country standards

[John Woodgate]

You are right.
 
With best wishes DESIGN IT IN! OOO – Own Opinions Only
  www.jmwa.demon.co.uk J M Woodgate and 
Associates Rayleigh England
 
From: John Allen [mailto:john_e_al...@blueyonder.co.uk] 
Sent: Saturday, May 21, 2016 9:36 PM
To: EMC-PSTC@LISTSERV.IEEE.ORG; 'John Woodgate' 
Subject: RE: [PSES] fire safety test methods for different country standards
 
BTW: if that “safety expert” had looked closer, I think he would have found 
that something like 60065 would have been far more difficult with which to 
comply than the correct standard (which was presumably probably some Part 2 of 
60335?).
 
John E Allen
W. London, UK
 
From: John Allen [mailto:john_e_al...@blueyonder.co.uk] 
Sent: 21 May 2016 20:44
To: EMC-PSTC@LISTSERV.IEEE.ORG  
Subject: Re: [PSES] fire safety test methods for different country standards
 
John
 
Re
“I had an enquiry once as to whether IEC 60065 could be applied to a 10 kW 
industrial fan heater, because that was the only standard their safety expert 
knew about.”
 
He was a “safety expert”?  I’m not, but at least I know more than that :(!
 
John E Allen
W. London, UK
 
From: John Allen [mailto:john_e_al...@blueyonder.co.uk] 
Sent: Saturday, May 21, 2016 7:47 PM
To: EMC-PSTC@LISTSERV.IEEE.ORG  
Subject: Re: [PSES] fire safety test methods for different country standards
 
Rich
 
With respect to actual testing of the materials in the enclosure, that was also 
impractical because there was (still is) a wide range of lengths and diameters, 
which were always very well populated because they were (are) made as compact 
as possible for the intended applications. Therefore we were pretty happy that 
the same principles as outlined in my previous email did apply across the range.
 
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Re: [PSES] fire safety test methods for different country standards

[John Allen]

BTW: if that “safety expert” had looked closer, I think he would have found 
that something like 60065 would have been far more difficult with which to 
comply than the correct standard (which was presumably probably some Part 2 of 
60335?).

 

John E Allen

W. London, UK

 

From: John Allen [mailto:john_e_al...@blueyonder.co.uk] 
Sent: 21 May 2016 20:44
To: EMC-PSTC@LISTSERV.IEEE.ORG
Subject: Re: [PSES] fire safety test methods for different country standards

 

John

 

Re

“I had an enquiry once as to whether IEC 60065 could be applied to a 10 kW 
industrial fan heater, because that was the only standard their safety expert 
knew about.”

 

He was a “safety expert”?  I’m not, but at least I know more than that L!

 

John E Allen

W. London, UK

 

From: John Allen [mailto:john_e_al...@blueyonder.co.uk] 
Sent: Saturday, May 21, 2016 7:47 PM
To: EMC-PSTC@LISTSERV.IEEE.ORG
Subject: Re: [PSES] fire safety test methods for different country standards

 

Rich

 

With respect to actual testing of the materials in the enclosure, that was also 
impractical because there was (still is) a wide range of lengths and diameters, 
which were always very well populated because they were (are) made as compact 
as possible for the intended applications. Therefore we were pretty happy that 
the same principles as outlined in my previous email did apply across the range.

 

-


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Re: [PSES] fire safety test methods for different country standards

[John Allen]

John

 

Re

“I had an enquiry once as to whether IEC 60065 could be applied to a 10 kW 
industrial fan heater, because that was the only standard their safety expert 
knew about.”

 

He was a “safety expert”?  I’m not, but at least I know more than that L!

 

John E Allen

W. London, UK

 

From: John Allen [mailto:john_e_al...@blueyonder.co.uk] 
Sent: Saturday, May 21, 2016 7:47 PM
To: EMC-PSTC@LISTSERV.IEEE.ORG
Subject: Re: [PSES] fire safety test methods for different country standards

 

Rich

 

With respect to actual testing of the materials in the enclosure, that was also 
impractical because there was (still is) a wide range of lengths and diameters, 
which were always very well populated because they were (are) made as compact 
as possible for the intended applications. Therefore we were pretty happy that 
the same principles as outlined in my previous email did apply across the range.

 

-


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Re: [PSES] fire safety test methods for different country standards

[John Woodgate]

RE:
The odd thing that I noted very clearly at the time was that the standard did 
not include any concept of a real partially- or fully-sealed enclosure where 
any internal fires could be contained within the enclosure without external 
flame spread or other related hazards.  That, I thought (still do) was a major 
oversight by the standard developers who had adopted the 60950 enclosure 
requirements almost verbatim and without full consideration of the very wide 
range of equipment to which the standard might then be applied.
 
Unfortunately, this often happens, and if you draw attention in the committee 
to the fact that all the necessary work hasn't in fact been done by another 
committee, you may not be overly popular.
 
I had an enquiry once as to whether IEC 60065 could be applied to a 10 kW 
industrial fan heater, because that was the only standard their safety expert 
knew about.
 
With best wishes DESIGN IT IN! OOO – Own Opinions Only
  www.jmwa.demon.co.uk J M Woodgate and 
Associates Rayleigh England
 
From: John Allen [mailto:john_e_al...@blueyonder.co.uk] 
Sent: Saturday, May 21, 2016 7:47 PM
To: EMC-PSTC@LISTSERV.IEEE.ORG
Subject: Re: [PSES] fire safety test methods for different country standards
 
Rich
 
With respect to actual testing of the materials in the enclosure, that was also 
impractical because there was (still is) a wide range of lengths and diameters, 
which were always very well populated because they were (are) made as compact 
as possible for the intended applications. Therefore we were pretty happy that 
the same principles as outlined in my previous email did apply across the range.
 

-

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discussion list. To post a message to the list, send your e-mail to 


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Re: [PSES] fire safety test methods for different country standards

[John Allen]

Rich

 

With respect to actual testing of the materials in the enclosure, that was also 
impractical because there was (still is) a wide range of lengths and diameters, 
which were always very well populated because they were (are) made as compact 
as possible for the intended applications. Therefore we were pretty happy that 
the same principles as outlined in my previous email did apply across the range.

 

Also, something not mentioned in that email was that the calculated typical 
worst-case case outer shell temperature rise due to internal ignitions was less 
than 1C – which meant that there was no risk of that rise causing ignition of 
any surrounding material.

 

The odd thing that I noted very clearly at the time was that the standard did 
not include any concept of a real partially- or fully-sealed enclosure where 
any internal fires could be contained within the enclosure without external 
flame spread or other related hazards.  That, I thought (still do) was a major 
oversight by the standard developers who had adopted the 60950 enclosure 
requirements almost verbatim and without full consideration of the very wide 
range of equipment to which the standard might then be applied.

 

In response to your last para, those were self-certification jobs to EN 
61010-1:2010 – which, fortunately, allows the risk assessment approach to 
issues where you can’t comply with chapter and verse of the standard! So it was 
down to us to decide whether the construction was adequate – and we were!

 

John E Allen

W. London, UK

 

 

From: Richard Nute [mailto:ri...@ieee.org] 
Sent: 21 May 2016 18:32
To: 'John Allen'; EMC-PSTC@LISTSERV.IEEE.ORG
Subject: RE: [PSES] fire safety test methods for different country standards

 

 

 

Hi John:

 

 

Thanks for your comments.  

 

In the end, the “solution” was a different sort of pragmatic approach because 
the boards were always enclosed in hermetically sealed high pressure (10,000 
psi+) / temperature (180C+) -resistant stainless steel tubes which have very 
little free air volume inside them. 

 

That means that there is very little free oxygen for component fires to use, 
and calculations proved that ignitions involving all the flammable material 
within the enclosures would exhaust that oxygen well before fires could 
develop, and also the way the enclosures are built and sealed means that flames 
or flammable material could not escape unless there had first also been very 
substantial external physical damage.

 

This is another option.  Build a fire inside the equipment and see what 
happens.  I use a fire-starting tablet or pellet (I’ve forgotten the name).  An 
enclosure with minimum openings that would allow replenishment of oxygen will 
suffocate the fire once the internal oxygen is used up by the fire.  The 
enclosure does not need to be sealed.  Usually, such construction will not have 
very much empty space and therefore relatively little initial oxygen to feed 
the fire.  (I used such testing to prove that a circuit fire would not ignite 
an HB enclosure.)

 

This is another situation where one can show that a fire will not spread very 
far beyond the initial fuel.

 

Whether or not this is accepted as compliance with the standard will depend on 
the certification engineer and the policies of the certification house (and 
your ability to convince them that the construction is adequate).  

 

 

Rich

 

 


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Re: [PSES] fire safety test methods for different country standards

[Richard Nute]

 

 

Hi John:

 

 

Thanks for your comments.  

 

In the end, the “solution” was a different sort of pragmatic approach because 
the boards were always enclosed in hermetically sealed high pressure (10,000 
psi+) / temperature (180C+) -resistant stainless steel tubes which have very 
little free air volume inside them. 

 

That means that there is very little free oxygen for component fires to use, 
and calculations proved that ignitions involving all the flammable material 
within the enclosures would exhaust that oxygen well before fires could 
develop, and also the way the enclosures are built and sealed means that flames 
or flammable material could not escape unless there had first also been very 
substantial external physical damage.

 

This is another option.  Build a fire inside the equipment and see what 
happens.  I use a fire-starting tablet or pellet (I’ve forgotten the name).  An 
enclosure with minimum openings that would allow replenishment of oxygen will 
suffocate the fire once the internal oxygen is used up by the fire.  The 
enclosure does not need to be sealed.  Usually, such construction will not have 
very much empty space and therefore relatively little initial oxygen to feed 
the fire.  (I used such testing to prove that a circuit fire would not ignite 
an HB enclosure.)

 

This is another situation where one can show that a fire will not spread very 
far beyond the initial fuel.

 

Whether or not this is accepted as compliance with the standard will depend on 
the certification engineer and the policies of the certification house (and 
your ability to convince them that the construction is adequate).  

 

 

Rich

 

 


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Re: [PSES] fire safety test methods for different country standards

[Richard Nute]

 

 

Hi Scott:

 

 

“In general, the users and testing houses are referring to the rating of UL 
yellow card rather than the actual test on individual final designed pcb.  
Should we use it to object their normal practice.  How often is it successful?”

 

Testing in place is a once-per-product-model (and board design) test.  Passing 
the test will depend on how much copper clads the epoxy versus exposed epoxy.  
Only boards with lots of copper are likely to pass.  So, it is an “iffy” test 
and the outcome cannot be predicted with certainty.  

 

As a general rule, use a board with ratings prescribed by the standard.  Where 
you must use a rating not prescribed by the standard, or you are using a 
non-rated board, and if the board design uses lots of copper, then testing the 
completed board in its end-product orientation may pass the flammability test.

 

 

Rich 

 

 


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Re: [PSES] fire safety test methods for different country standards

[John Allen]

Rich

 

Thanks for the info – which I had not realised before.

 

However, even if I had known, I don’t think it would have helped much in that 
particular situation which involved a wide range of board designs and layouts 
produced in very small quantities of each – so we could not have tested every 
one even if we had had the right test facilities, which we did not.

 

In the end, the “solution” was a different sort of pragmatic approach because 
the boards were always enclosed in hermetically sealed high pressure (10,000 
psi+) / temperature (180C+) -resistant stainless steel tubes which have very 
little free air volume inside them. 

 

That means that there is very little free oxygen for component fires to use, 
and calculations proved that ignitions involving all the flammable material 
within the enclosures would exhaust that oxygen well before fires could 
develop, and also the way the enclosures are built and sealed means that flames 
or flammable material could not escape unless there had first also been very 
substantial external physical damage.

 

PS: the problem with the V-1 boards was that the flame-retardants apparently 
break down over time at the high operating temperature in which the enclosures 
operate (down oil and gas drill holes), and the by-products then aggressively 
attack the components on the boards and cause them to fail.

 

John  E Allen

W.London, UK

 

From: Richard Nute [mailto:ri...@ieee.org] 
Sent: 21 May 2016 03:01
To: EMC-PSTC@LISTSERV.IEEE.ORG
Subject: Re: [PSES] fire safety test methods for different country standards

 

 

 

In my last job I tried to do something similar w.r.t. PWB materials for 
applications where V-1 or better materials aren’t any good because the 
retardants result in reduced service lives in hostile equipment environments, 
whereas some specific (and very special!) HB materials last much longer.

 

A PWB with lots of copper will pass the 94V-1 or 94V-0 tests even if the base 
material is 94HB!  The copper acts as a heat-sink and prevents oxygen from 
mixing with evolved gasses from the epoxy.  Test in place (vertical or 
horizontal).  

 

 

Rich

 

 

 

 

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