About This Archive  |	DCHAS-L 2016 Index   |	DCHAS-L Yearly Index
Search All Posts:   Advanced Search     Disclaimer

Check out Safety Emporium for your N95, N99, and face shield needs.

Previous by Date: Subject: [DCHAS-L] Chemical Safety headlines from Google (10 articles) Date: Monday, October 24, 2016 at 8:06:08 AM Author: DCHAS Secretary <secretary**At_Symbol_Here**DCHAS.ORG>

Next by Date: Subject: Re: [DCHAS-L] Lab PPE Update and Request Date: Mon, 24 Oct 2016 17:25:57 +0000 Author: Debbie M. Decker

From: "Mathews, Mark E."
Re: Another look at runaway hotplates

The email below from Kimberly Brown about hot plate failures was forwarded to me last Friday. I am not a researcher but work on electrical safety issues at Oak Ridge National Laboratory. I left a phone message for Ms. Brown (her email address is not shown below), but I also wanted to take this opportunity to make contact with a larger audience that is interested in this serious matter.

We have also experienced several hot plate failures at our site. The most serious failure occurred in April 2014 when a stirring hot plate that appeared to be turned off had either remained on after its last use or had turned itself on (more on that later). A beaker placed on the plate to stir (not heat) overheated and resulted in an explosion that destroyed the fume hood and caused major damage to the lab. Fortunately, no one was in the lab at the time of the explosion. We had a subsequent incident where a hot plate heating element remained on (or possibly turned itself on) even with the control switch turned to the ‰??off‰?? position.

Discussions with our R&D personnel have indicated that these hot plate failures probably happen rather frequently; the researcher or technician realize the plate is not correctly functioning, so they dispose of it and purchase another. But, we have not collected hard data on how often this occurs or what type of failure it was.

There are several failure modes for hot plates as documented in the reports referenced below. An important solution for hot plates failing to turn off (or turning themselves on) with the temperature control switch in the off position would be to revise the product standard to which most hot plates are evaluated (IEC 61010.1; the U.S. version is UL 61010-1). I‰??ve been in contact since last spring with an engineer at Underwriters Laboratories about revising 61010-1. UL‰??s version of 61010-1 is only licensed from IEC, so any technical changes will have to be made to the IEC version. I did learn that the committee responsible for 61010-1 assumes that hot plates will be unplugged when not in use (in other words, the power plug - not the temperature control switch - serves as the power ‰??disconnecting means‰??). I think that the standard should require the power circuit for heating elements be mechanically opened (with a switch, contractor, etc.) when the control switch i!
s turned to the off position. Several hot plates we have analyzed utilize a solid state switching component (triac) to turn off power to the heating element. It is well-known in the electronics universe that a common failure mode for triacs is to fail shorted (i.e., in the ‰??on‰?? position), and this failure mode could result in a hot plate not turning off although it appeared to be off. [We developed a short slide show about how this can occur. I‰??ll ask if I can share that, although I think one version may have made its way to the web already.]

While the issue of a ‰??runaway‰?? hot plate (failure while in use) will need a separate solution, a revision of 61010-1 could possibly address that, too.

Last spring I provided what info I had gathered (including the papers mentioned below) and sent them to the UL engineer so he could take that to the IEC committee. I checked with him a few weeks ago, and he said that the committee had taken no action yet.

I would like to discuss this issue with your organization to see if the larger R&D community would be interested in compiling a list of more recent events involving hot plates and then present that body of evidence to the IEC along with a request to revise 61010-1.



Mark Mathews
Electrical Authority Having Jurisdiction
Safety Services Division
Oak Ridge National Laboratory
Office 865-574-8412
Cell 865-413-3205

Subject: [DCHAS-L] Another look at runaway hotplates

Hello:

In the past 2 years on our campus we‰??ve had 1 suspected and 2 confirmed ‰??runaway‰?? hotplate events in chemistry labs (2 resulting in fires). In our case, each device was a model manufactured by Corning (PC320 or PC420-D). (We have not seen the same behavior with hotplates manufactured by other companies, but it‰??s worth noting that the Corning models are popular on our campus, so that could be the reason that the issue was isolated to this manufacturer.)

I am familiar with the April 2015 DCHAS-L thread [subject: Runaway Hot Plates] and the various warnings and studies that are frequently cited on this topic (see bottom of this message for more on that). For those who aren‰??t familiar with these, quick recap: We‰??re not the only ones who have noticed this problem.

My question is this: Isn‰??t it surprising that there was never a safety recall issued (or a law suit for that matter)? Does anyone know if that was ever explored?

We recently did a presentation to our chemistry department about these malfunctions, and I‰??m starting to get questions from the researchers about recall or class-action suits. The best I can figure is that it‰??s hard to prove that manufacturer recommendations for care and use of the equipment have been followed to the letter. For instance, a used-and-abused piece of equipment that malfunctions in this manner would probably be considered compromised, right(?) Similarly, if the hotplates are not unplugged when not in use, even though the user manual may recommend that they should be(?), is there really a case that can be made against the manufacturer?

On a related topic, we aren‰??t asking labs to replace all of their devices, but we do want to recommend a preferred product for higher-risk operations or environments. In reviewing the 2007 UC Santa Cruz study on hotplates (excerpt below) I see that the question of ‰??processor watchdogs‰?? was raised. Does anyone have any additional information about the current state of the design in the popular models (visa vi processor watchdogs)? I know that IKA boasts ‰??redundant processors‰?? and ‰??over-temperature safety controls‰??, but I haven‰??t been able to figure out whether this exactly controls for the inherent design flaw described in the report (see excerpt below).

Thanks for any additional information you can lend to this conversation.

Kimi Brown
(Kimi Bush)
Lab Safety Specialist
Environmental Health and Radiation Safety
University of Pennsylvania
3160 Chestnut St., Suite 400
Philadelphia, PA 19104-6287
Office: 215-746-6549
Voice/cell/text: 215-651-0557
fax: 215-898-0140

---
This e-mail is from DCHAS-L, the e-mail list of the ACS Division of Chemical Health and Safety.
For more information about the list, contact the Divisional secretary at secretary**At_Symbol_Here**dchas.org

Previous post   |  Top of Page   |   Next post