Ask the Expert Question-and-Answer Archive (TRI)

by Joelie Zak, Scientific Control Labs, Inc.
April, 2002

Lead in Solder

Q. I was recently at an EPA training. The most important subject in the minds of most attendees was the new lead rule. However, I left this training more confused then ever. I hope that you can help.

The presenters stated that when calculating the thresholds in relation to solders that are used, you must also calculate for PbO. They claimed that there was a 1:1 ratio of the amount of PbO emitted to air for each pound leaded solder that was used. Is this true? I have yet to find any back up documentation on this. Do you know of any?

A. I have not been able to find any documentation that would say that soldering always produces lead monoxide (as opposed to lead fume or other byproduct). This includes EPAs own Lead TRI guidance document. However, the EPA instructor is partially correct. The total weight of the lead compound that may be "coincidentally" manufactured (even as a byproduct) must be counted towards threshold determination. What the presenter was saying is that for every 1 lb. of lead soldered, 1.08 pounds of lead monoxide is generated (Molecular weight of PbO 223.2 divided by MW of Pb, 207.2 = 1.077).

You should probably get ahold of one of these presenters to find out if this was just an example on threshold determination, or if they actually have data/documentation on lead compounds formed during soldering operations. If they dont, I would just count the amount of lead in solder used, since this is the best available information.

Overall, there is very little air emission information on soldering, brazing and welding. However, if I can obtain any further information about this, I will certainly forward it to you.