I seek advice and opinions from fellow safety minded people.

Our typical product has a metal chassis which is constructed as a Fire 
Enclosure (laboratory equipment 61010-1). On the back is a cutout for a cooling 
fan/blower mounted in the cutout. The fan is 24Vdc, certified by several safety 
agencies, and has a finger guard.  This is typical configuration on most 

Now, our customers want us to install an externally changeable Air Filter on 
the outside surface of our instrument where the fan is mounted to filter dust 
particles from the incoming air. We already perform Blocked Vent and Stalled 
Fan tests to insure no hazards are caused from the rise in internal 

But what type of Fault Testing or Risk assessment needs to be done regarding 
the filter?  With the filter removed, the instrument passes the construction 
requirements for a Fire Enclosure. But with the filter installed and because of 
its close proximity to the fan/blower;

1.        does this filter have to meet Flammability requirements? Does the 
filters have to be certified (expensive)? UL 94 HF-1?, UL 94 HF-2?, UL 900?  
How are these ratings/certifications viewed outside of North America?  Will 
they have to meet local requirements??

2.       If the fan/blower is certified and limited energy circuit does the 
filter have to have any kind of rating or certification? In other words, with a 
certified fan/blower, do I have to consider the fault condition of the fan 
failing in a way where it could catch the filter on fire?

3.       How is a fault and/or risk assessment performed on an air filter?

4.       Are we responsible to consider the hazards from a burning filter when 
it is dirty? How would we know what type of contaminates might collect in a 

5.       If the filter we provide is UL 94 HF-1 and UL 900 rated/certified, 
what would stop our customer from replacing it with whatever filter they 
wanted? Are we responsible to include a warning label and statements in the 
manual regarding this?  Example, "Use only Air Filter part number XYZ".

6.       Any other suggestions or issues that we are not considering?

Thanks in advance. Have a nice day.

The Other Brian
LECO Corporation Notice: This communication may contain confidential 
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