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Aluminum/steel grindings. How dangerous?


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I'm in need of information. I understand that a mixture of steel and aluminum is dangerous.

Would someone please explain the dynamics going on here. What concentration? How

does it ignite? How violent a reaction? If you sand or grind steel and then want to sand or grind

aluminum does the dust collector need to be cleaned out?

 

Thanks to anyone who can shed some light here for me.

 

Bill

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It's not a mixture of steel and aluminum filings that are dangerous it's iron oxide and aluminum filings, and they are theoretically dangerous. The combination is call Termite and it burns at the temperature of iron near the boiling point and supplies it's own oxygen for the reaction and is nearly impossible to put out. The thing is that it is very hard to ignite the mixture. A video on Youtube showed guys using a strip of burning magnesium to get it started; I doubt that a spark from a grinder would do the trick. That said, I doubt that I would allow any large amount of steel/iron filings and aluminum grindings to accumulate together for a long time because the steel/iron will rust (iron oxide) and, if the two metals are in about equal portions, form a pile of Thermite. After watching a video of a large flower pot full of the stuff burn it's way through a engine block, it's nothing to have laying around the house.

 

Doug Lester

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Thanks Doug,

 

My dust collector has a water-filled base so I guess I'm ok.

High temps needed to ignite are not reached. It gets a little

sludgey but is always cool.

 

Bill

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There are routine warnings about dust collection systems where the fine particles have been known to cause explosive overpressure in the system. Iron fines that have oxidized and aluminum dust would be a combination of concern. Most big dust collection systems have explosion vents built in.

 

http://www.osha.gov/dts/shib/shib073105.html scroll down to story number 4. Any kind of dust can be explosive.

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Ehh, heres some food for thought :huh:

 

 

Department of Energy Richland Operations Office

Lessons Learned Issued in 2001

Fireball from Aluminum Grinding Dust

 

Date: September 21, 2001

Identifier: 2001-RL-HNF-0036

 

Lessons Learned Statement:

Aluminum grinding dust can create a serious explosive fire hazard when it is mixed with steel or iron grinding dust.

 

Discussion of Activities:

A safety coordinator at the Esso Oil Company plant in Longford, Australia, was using a belt grinder in his home workshop to smooth the edge of a hacksaw cut on a 2" length of 1.5" angle iron. He had been grinding for about 1.5 to 2 minutes when there was a loud "THUMP" accompanied by an approximately 2-foot diameter brilliant yellow orange fireball. The fireball lasted no more than 1 second and then completely extinguished itself. It completely enveloped the machine, his hands to half way up his forearms, and the front of his torso.

 

Injuries included deep second-degree burns to about 60% of the victim's left hand and 50% of his right hand and first degree burns to his neck, chin, cheeks, lips, and the end of his nose. The right cuff of his shirt was smoldering, his face felt a burning sensation, and he could hear the front of his hair sizzling. Nothing on the bench was burning. A few streaks of white powder were deposited on the bench top and on a few items lying on the bench. The workshop was filled with dense white smoke with very little odor. His fingers and the ends of his thumbs escaped relatively unscathed as they were protected from the heat flash. He was wearing glasses, which protected his eyes. He also lost half his moustache, one of his eyebrows, and about 1 inch off the front of his hair. His eyelashes were curled by the heat but not singed. The burns to his face were caused solely by radiant heat, as the fireball did not come that high.

 

Analysis:

A few days before the event, the man's son had ground the heads off about twelve aluminum pop rivets. Finely divided aluminum mixed with finely divided ferrous oxide (the black powder residue from grinding steel) produced a compound called thermite. Thermite is used to fill incendiary bombs and is used commercially to weld large steel items. It burns at approximately 3500C (6300F), hence the extensive burns from such a short exposure time.

 

Recommended actions:

The victim recommended that the manufacturer of the grinding wheel should include a very strong warning about the dangers posed by grinding steel after having ground aluminum. That warning should include precautions to thoroughly clean the grinding machine of all aluminum dust before grinding iron or steel.

 

Estimated Savings/Cost Avoidance: N/A

 

Priority Descriptor: YELLOW/Caution

 

Work / Function: Machining and Fabrication

 

Hanford-Defined Category: N/A

 

Hazard(s): Fire / Smoke

 

ISM Core Function(s): Analyze Hazards; Develop/Implement Controls

 

Originator: Bruce Robinson, Longford Plant Safety Coordinator; Longford Ext. 6348; Fax (03)5149 6496.

Introduced into the DOE LL system by Fluor Hanford, Inc.

 

Contact: Project Hanford Lessons Learned Coordinator; (509) 373-7664; FAX 376-6112; e-mail: PHMC_Lessons_Learned@rl.gov

 

Authorized Derivative Classifier: Not required

 

Reviewing Official: John Bickford

 

Keywords: grinder, thermite, aluminum dust

 

References: Bechtel Australia Alert 01, Grinder work with Aluminium

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Well, THAT certainly puts a different slant on things!! :blink: So it

appears that a thorough cleaning between grinding sessions is

not just a good idea, but really important.

 

Fireballs are only good coming from the muzzle of a black

powder cannon.

 

Thanks to all for the information. As usual, good help is

easy to find here. Thanks again.

 

Bill

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