Welding on oil pan while on car

Actually, no, it is very easy to know how much CO2 you would have, if you take a few seconds and look at the numbers.

The volume of gas released (at room temp and pressures) from one cubic centimeter of dry ice is about 0.83 liter (about a fifth of a gallon). If you assume that a handful of dry ice is about the volume of a golf ball (a golf ball being about 30 cubic centimeters), and that "a few handfulls" is three golf ball size chunks of dry ice, then you are looking at the amount of CO2 liberated being about 74 liters, or about 20 gallons.

As for the mixing of the gasses, dry ice sublimates slowly enough that if you leave the tank undisturbed with a small orifice for O2 to leave (to minimize drafts), you can reasonably assume that a sufficient amount of 02 has been displaced.

You can give yourself an additional safety factor if you wish; dry ice is cheap and readily available enough.

Jon

"Jon Danniken" wrote: The volume of gas released (at room temp and pressures) from one cubic

^^^^^^^^^^^^^^^^^^^ Actually, from my drinking experience, I believe a "fifth" equals 750 cc.

As far as displacing ALL the oxygen is concerned--you don't have to. You need to displace most of it, so the remaining content of the tank is outside the ignition limits. AMHIKT (Ask me how I know this.) Okay, I'll tell you. When I ws a grad student at Cal, I worked on a project for the Air Force in which we studied what happens inside a fuel tank when an ignition source (such as a tracer bullet) goes into a tank. The object was to fill the vapor space in aircraft tanks with a non-combustible mix. We used spark plugs in most of our tests, and actually fired bullets in many of the tests.

A mechanic at a friend's shop was welding on a pan and the vapor went off. It shot out a burst of flame catching him square in the face. Not pretty.

What is wrong with soldering using big coppers, heated a few feet away on the bench? I did this with a cracked fuel tank, although the assistant was heating the coppers 40 feet away and above floor level due to gas vapor being what it is.

Good choice too. Brazing, that is.

Unbeknownst to many, almost all (if not all) of the hardware store fasteners are leaded steel. Welding to leaded steels is possible, but one never gets the original base material ductility or strength in welds to leaded steels and there is the significant potential for undetected hot cracking. Commercial fasteners are made by folks who are concerned about their tooling and not whether or not the fasteners will work well in a welded application. Leaded (free machining) steels are much easier on automated screw machines and the factories can get many, many more parts per setup than if they use "regular" steel grades.