printech, January, 2004
Re: Offset Powder Emission

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From: Gary Jones ( )
Date: Fri, 23 Jan 2004 17:02:52

I did some digging on your question and did not come with a definitive answer. Basically, you need to know what the transfer rate is of the spray powder to the sheet. What I found out is that there are so many variables associated with answering this question is that there is no one good answer. However, there are several approaches that could be taken to respond to the request for info:

1. Measure the amount of powder being emitted. If the correct circumstances exist, the amount of powder over a period of time and jobs could be measured. This alternative is not the most cost effective, but it will give you the most accurate answer.

2. Use industrial hygiene data from indoor air quality testing. If you have conducted any employee exposure studies to spray powder, you could use this data as an estimate of what could be exhausted. This data will give you a concentration of particulate matter in the air in mg/cubic meter. Assuming that all of what is measured is spray powder, there could be paper and other dust in the sample, and that this concentration of dust exists in the delivery area of the press, you could multiply this by the exhaust rate of the fan to get a mass emission rate.

Assuming that you are in compliance with OSHA's PELs, the employee exposure limit for cellulose (spray powder) is 5 mg/cubic meter. This approach is not the most accurate as it is difficult to equate employee exposure with mass emission rates, but at least it is based on a measured value.

3. I had a conversation with a spray powder manufacturer to determine if they had ever done any measurements to answer this question. They did not have any specific data, but said that under ideal conditions, there should be a transfer rate of 85%. They said that many operations do not work under ideal conditions. This would be the lease accurate approach as it is hard to describe what is ideal and if you are meeting this conditions.

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