On 17 Mar 2006 11:03:49 -0800, wrote:

With the semi disposable 4251, how long would it last with dusty
conditions?

It's hard to gauge, but I would say roughly a third longer than those
with disposable cartridges.

So, the semidisposables are good for occasional work. If you are
working regularly with dust, they will become less economic since the
disposable cartridges are about half the price of the semidisposable
masks,


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..andy