Re: Re:
Posted by
Ian Wright
on 1999-10-23 02:50:17 UTC
Hi,
In my experience, trying to detect and extinguish dust fires is pretty much
impossible and the only way to go is to prevent the possibility of them
starting. This means detecting a heat build-up withing dust collectors and
eliminating any source of ignition in the dust path. Most fires in cyclones
and silos are caused because they are not emptied and cleaned out often
enough and usually because the dust is allowed to get damp. This causes
internal heating in the mass of wood dust and, if conditions are right, can
get hot enough for flying dust to spontaneously ignite. Some types of wood
are worse from this point of view than others (usually some of the more
exotic hardwoods) . In Sheffield, the cutlery industry was very susceptible
to problems of this type and the mixture of lint from buffing wheels,
greases from the buffing compounds, mineral grits and metal particles caused
regular cyclone fires. I once saw a smouldering cyclone explode when a
(rather dim) firemen thought he would extinguish it by lifting the lid and
squirting water in. As he lifted the lid it raised a cloud of dust which
just exploded in a sheet of flame throwing the fireman off his ladder and
badly burning him. Just like watching a movie special effect! Of equal
importance to maintenance of dust extraction kit is keeping the workshop
clean and regularly cleaning down any ledges where dust can accumulate - it
only takes a gust of wind through the door to raise a cloud of dust which
could explode if any flame or cigarette is around. Several years ago I saw
the remains of a flour mill which had suffered from such an explosion.
Finally, any extraction equipment for wood dust should be protected against
electrostatic build-up. The friction of wood particles flying along ductwork
can generate electrostatic sparks and miniature lightning storms which can
be sufficient to ignite the dust.
Ian
--
Ian W. Wright
Sheffield UK
In my experience, trying to detect and extinguish dust fires is pretty much
impossible and the only way to go is to prevent the possibility of them
starting. This means detecting a heat build-up withing dust collectors and
eliminating any source of ignition in the dust path. Most fires in cyclones
and silos are caused because they are not emptied and cleaned out often
enough and usually because the dust is allowed to get damp. This causes
internal heating in the mass of wood dust and, if conditions are right, can
get hot enough for flying dust to spontaneously ignite. Some types of wood
are worse from this point of view than others (usually some of the more
exotic hardwoods) . In Sheffield, the cutlery industry was very susceptible
to problems of this type and the mixture of lint from buffing wheels,
greases from the buffing compounds, mineral grits and metal particles caused
regular cyclone fires. I once saw a smouldering cyclone explode when a
(rather dim) firemen thought he would extinguish it by lifting the lid and
squirting water in. As he lifted the lid it raised a cloud of dust which
just exploded in a sheet of flame throwing the fireman off his ladder and
badly burning him. Just like watching a movie special effect! Of equal
importance to maintenance of dust extraction kit is keeping the workshop
clean and regularly cleaning down any ledges where dust can accumulate - it
only takes a gust of wind through the door to raise a cloud of dust which
could explode if any flame or cigarette is around. Several years ago I saw
the remains of a flour mill which had suffered from such an explosion.
Finally, any extraction equipment for wood dust should be protected against
electrostatic build-up. The friction of wood particles flying along ductwork
can generate electrostatic sparks and miniature lightning storms which can
be sufficient to ignite the dust.
Ian
--
Ian W. Wright
Sheffield UK
----- Original Message -----
From: Ray Henry <rehenry@...>
>
> Around these parts (Michigan U.P.) we often read about wood dust fires
> creating disasters. Last year a furniture factory blew apart a 40' tall
> cyclone collector. They had some fire protection installed but it was not
> fast enough acting for the kind of dust they were moving. Lucky that it
> was the night shift and no one was hurt.
>
> IMO If you do much wood routing it'd pay you to have some automatic
> protection.