/ Home & Energy

Could you be damaging the glass of your oven door?

Oven door

You have to be unlucky for your oven door to shatter out of the blue. But if it does, it’s memorable – and not in a good way. While finding the root cause can be tricky, there are ways to lower the likelihood of this happening to you…

A few months ago we asked you to contact us if you’d experienced your oven door shattering.

An interesting discussion on Which? Conversation kicked off, where many of you told us about your experiences of shattering doors.

Since then, we’ve spoken to experts from the Centre for Glass Research at the University of Sheffield who have given us the low-down on exactly how strengthened glass is made, why it can shatter and the difficulties of pinning down the precise cause.

Oven doors

Ovens doors are made from tempered glass, which is stronger than normal glass. Its compressed outer surface makes it less likely to break, but if it does, pieces of glass can fly out onto your kitchen floor.

Fortunately, the individual pieces have blunt edges, so are less likely to cause a severe cut than normal glass.

The only way to be sure of the cause of failure is for the glass to undergo fractographic analysis. But this requires all the broken pieces to be gathered up to enable reconstruction. In the average home, this is next to impossible to do.

What can you do to avoid it happening to you?

Well for starters, we found that 65% of Which? members who clean their oven doors by hand use a scourer. Scrubbing at glass with something abrasive such as a scourer is tempting, especially if you have stubborn cooking grime to banish. But scouring is best avoided as it introduces microscopic scratches in the glass which can cause it to fail spontaneously some time later.

Other easy things to steer clear of is letting the door slam shut, or bash into the metal shelves. And if your door opens horizontally, it can be convenient to place a dish there, but this can compromise the glass, leaving it more vulnerable to shattering.

What to do if it happens to you

If your oven door does shatter and the appliance is out of warranty, don’t bank on a sympathetic response.

Worst-case scenarios from Which? members included long waits, pricey repairs and manufacturer apathy, though occasionally a manufacturer stepped up to the mark and supplied a quick repair free of charge.

We are continuing to push manufacturers to give a consistent and helpful response, so please tell us if your oven door has shattered and what happened next.

Has your oven door shattered? What did you do? How do you clean the glass on your oven door?

Comments
Profile photo of PatrickTaylor
Member

Much appreciated.

Useful science which I hope Which? will provide more often in theses sorts of cases. The horizontal glass surface is an interesting insight, and I have in the past used 0000 grade wire wool on glass as it is one of its recommended uses. Did Which? pose this question?

As I complete the annual[?] survey on major appliances what were the results from the 2015 one on shattered oven door glass?

That sort of information may provide a feel for how uncommon it is, or perhaps highlight a manufacturer. Anyway please can we have the survey information as when I complete them I do expect Which? to use the results fully.

Profile photo of wavechange
Member

Thanks for this follow-up Conversation, Jane.

When I was at school, I witnessed a Duralex drinking glass explode in front of me when it was on a shelf. I discovered that toughened glass can fail in this way when scratched or knocked. Since then, I have been wary of glass breakage. My approach is to do my best to try to protect doors from spatter and if this does happen to clean them as soon as they have cooled using detergent on a cleaning pad intended for non-stick pans.

Profile photo of malcolm r
Member

Normal soda lime glass is not good at resisting sudden temperature changes – such as dropping cold liquid on a hot door. Nor is it good at resisting impact. The toughening process puts the outside surfaces into tension and makes it much more resistant in these respects. Hence its usefulness in many applications, like ovens If the surface “skin” is damaged – the edge nicked, the surface scratched for example , energy is released and the glass crazes in small pieces with safe edges. Remember what happened to older cars’ windscreens. I am surprised that they “explode” in the way described by some; normally when we tested toughened glass panels, by using a centre punch and hammer, they crazed but stayed intact, a bit like a jigsaw.

An alternative would be to use a low expansion glass to resist thermal shock, but it would need to be thicker to resist impact. Borosilicate (“Pyrex”) is commonly used, particularly where the product is not flat.

I hope this kind of excellent introduction will be repeated, where expert input is used.

I’d be interested to know just how many people have problems with shattering oven doors. This will give an idea of the size of any problem. Which? Connect is a survey group with over 30 000 members. They could be asked (I don’t remember if they have)
1. Do you have a freestanding or built-in oven with glass door(s)?
2. Has any of the glass suddenly shattered?
3. If it did break, did it stay more or less in situ or did it “explode” across the kitchen?
4. What make is your oven?

They could, in fact, ask all their members the same question through their magazine.

Profile photo of wavechange
Member

Borosilicate glass will indeed withstand thermal shock – for example putting a cold casserole on a hot oven door. Having had a considerable amount of specialist glassware made from borosilicate glass at work, I believe that it is the best choice for oven doors.

I presume that the reason that toughened glass sometimes remains in place and sometimes explodes results from differences in the tempering (heat treatment) used in different applications.

It would be interesting to know which type of glass different manufacturers use for their oven doors.

Profile photo of malcolm r
Member

Sorry; correction – the outside surfaces are put into compressive stress.

Profile photo of PatrickTaylor
Member

More statistically based information here:

“The Results.
The answer to a) above … The total number of jobs that have been undertaken by those 97 who responded to the survey was 295,334.
On average, those who responded have been an OVENU franchisee for six and a half years. Many have traded successfully for over 10 years.
Therefore, if we divide the total number of jobs done by the length of time as a franchisee, this shows that, on average, there were 45,436 jobs completed every year.
In answering b)… there were a total of 209 incidents where an oven door glass was broken. As a percentage, this is a reasonably tiny 0.07%. Put another way just 7 breakages for every 10,000 jobs undertaken…..or one every 1,428 jobs … that’s just less than 32 a year out of an average of 45,436 completed jobs.
Leading on to the answer to c)… 152 breakages of the 209 total were accidentally caused by the franchisees. Again, as a percentage, this works out to be just over 72% of all the instances where a breakage occurred.
This leaves just 57 instances out of 295,334 completed jobs where oven door glass shattered for no apparent reason. This figure is just under 9 cases a year.
As a percentage, the 57 ‘mystery’ cases represent just 0.02% … again, put in a slightly different way, a solitary ONE instance per 5,000 jobs undertaken.

And the possible causes seem very interesting commencing with production:
ovenu.co.uk/shattered-oven-door-glass-survey/

Profile photo of malcolm r
Member

Patrick, thank you! This is surely the kind of information Which? should be including in its reports and Convos so we can see things ino perspective? Do they not have the resources or the expertise to dig out such information or do they choose not to as it might spoil the headlines? They could ask their Members to help of course.

I think it is misleading to withhold useful information like this, and would like the way topics are presented to be much more balanced.

Profile photo of wavechange
Member

The whole report makes interesting reading: https://www.ovenu.co.uk/shattered-oven-door-glass-survey/

Toughened glass will ensure that there are no large shards to cause injury if breakage occurs, but the shock of an explosion could result in a user dropping food at extremely high temperature.

I wonder whether some manufacturers opt for borosilicate (e.g. Pyrex) glass or if there is a standard that demands use of toughened glass.

Profile photo of malcolm r
Member

The safety standard is BS EN 60335-2-6. It specifies a test for the glass, whether curved or flat, and whether loose or held in a frame. The test requires the use of a specified punch and hammer that is used to break a test panel; it requires that if the panel is loose, the number of crack free particles within a 50mmx50mm square number not less than 60. If the glass is held within a frame, it requires that none of the glass shall become released or dropped from their normal position. A thermal shock test is also specified.

This seems to include borosilicate or similar glass as well as toughened glass, providing they pass the tests.

Profile photo of wavechange
Member

Thanks Malcolm. This makes it clear that on breakage, the glass is intended to remain in place, so any door that exploded sending fragments of glass round the room is clearly non-compliant with the standard.

I do not know if borosilicate glass can be toughened by heat or chemical treatment. In scientific glassblowing using borosilicate glass it is normal to anneal glass (heating it to between the glass transition temperature and the deformation temperature followed by slow cooling) to remove stresses to reduce risk of cracking in use.

Profile photo of malcolm r
Member

The glass that is held in a frame is intended to remain in place when broken. So borosilicate say, that breaks into large shards must comply.

Boroslicate can be toughened but as it is a low expansion glass I don’t believe it will have the same characteristics as the higher-expansion soda lime.

I have never seen a toughened glass panel “explode” across a space. We used them widely, they are used a lot in larger window and door glazing, in car windows and used to be in windscreens. Whenever they broke or were broken they stayed in place, rather like a jigsaw. So “exploding” would not, in my experience, be normal. It would be interesting if Which? asked Sheffield University to comment on this.

Profile photo of wavechange
Member

I have seen broken toughened glass windows in cars and doors and the glass has either remained in position or mostly so. I have not seen a broken oven or washing machine door.

It would certainly be interesting to have more input from Sheffield, and Which? has already made contact here.

My experience as a schoolboy made it very clear that toughened glass can occasionally explode and I doubt that all the photos that can be turned up with a simple web search have been contrived.

Profile photo of PatrickTaylor
Member

I commend to you the USA where they have an excellent site for the public to report incidents. I have chosen Kenmore as apparently they have had a rising trend in an earlier period 2011-14 but AFAIR 62 in 2014. The installed base of Kenmore may of course be huge.

saferproducts.gov/ViewIncident/1626096

Also worth looking at is there overall approach here:
cpsc.gov

The lesson to be learned apparently is that there are facts available, including the major appliance survey by Which?, and that these details are actually important if there is to be a reputation of which members can be proud. Even if the Which? survey had a zero incident report the number and make of ovens could be provided as it is entirely possible members all have decent ovens.

The question is how far can the charity satisfy a seemingly mass-market approach without seeming very lightweight to the more technical paying supporters.

I have some serious disquiet about the quality of the robot vacuum reports which if I can access the Members forum I will post there. I will also put it on-line for those Which? subscribers who are not given access to the Community forum using my Google docs channel.

Profile photo of malcolm r
Member

I see no problem at all in providing comprehensive reports to satisfy members of all abilities. A summary can provide the basic information, and the details can then be dealt with in the body of the report. We should not dumb down reports nor construct them to suit only one group of people. If extensive information is available but too long for publication the website can be used. However I don’t see this as necessary in most cases.

Profile photo of wavechange
Member

Jane Darling has a report on exploding ovens in the October 2017 issue of Which? magazine.

I can accept that using toughened glass is of value providing it remains in place when broken. It is often referred to as safety glass because the pieces are unlikely to cause more than minor injury since sharp shards are never produced.

I presume that the tempering procedure must be inappropriate if toughened glass flies round the room when broken.

Profile photo of wavechange
Member

The inner door glass of an oven may be subject to scraping, abrasive materials and chemical cleaners that are typically highly alkaline. In contrast, the outer glass is unlikely to receive this harsh treatment and will not be subject to the same extreme temperatures. It would be interesting to see statistics for breakage of inner and outer door glass.

Apart from abrasion and impact, one reason given for spontaneous breakage of toughened glass is nickel sulphide inclusions: https://www.pilkington.com/resources/ats165spontaneousbreakage20130114.pdf We have discussed these before in the context of breakage of mobile phone screens.

Profile photo of alfa
Member

I don’t have time to read all the links in Patrick Taylor’s post, but some time ago, I found a discussion on shattering oven doors probably on a US website. They put the blame on the super-hot cleaning cycles. Some suggested that it could be the fixings that couldn’t handle the high heat.

Profile photo of KennethWatt
Member

Let me sum this up simply.

Glass can break. You can’t get away from that.

If you do not want the possibility of that, don’t buy an oven with a glass door.

It’s really very simple.

K.

Profile photo of wavechange
Member

Can you advise us on availability of ovens without glass doors?

I’m not too concerned but anyone who has suffered a breakage – particularly a spectacular one – might be interested in an oven without a glass door.

Profile photo of KennethWatt
Member

Very few do it now, mainly on very high end stuff into commercial and large range cookers only sadly as, customers demand glass doors.

I really don’t understand why but, they do.

K.

Profile photo of wavechange
Member

Range cookers were the only ones I could think of.

Member
Patrick Taylor says:
21 September 2017

This pretty much covers the subject and rather puts into context the “problem”. Whilst there may be a variety of cases caused by poor treatment by owners the underlying answer would seem to be available in 2001

Pilkington’s product brochure has long contained a warning note of such possible breakage. The current Product Guide (available on our website at pilkington.com/na , page 6 reads:
“ On rare occasions, heat – treated (tempered and sometimes even heat -strengthened) glass can break spontaneously, without any applied load, due to small inclusions that may be present in all float glasses.”

This of course means hundreds of metres of Press coverage and stories has essentially failed to mention this fact. The detail of how often per tonne of glass even gives a calcuable [roughly] occurrence.

Perhaps an article on household insurance cover and costs would actually be the worthwhile route.

I am disappointed that a simple reason why float glass, which I assume is what is treated and used for oven doors, breaks randomly is not front and centre in the article.

The apparent increase in incidence may be done to the greater thirst for filling the media with stories AND/OR larger glass-fronted doors increasing the possibility of a random breakage. My new Siemens oven door covers the full width of the oven.

And to reiterate what should be offered is Which? providing one point authoritative reference points for household matters.

Profile photo of malcolm r
Member

In a previous Convo I and others have said that inclusions in glass (sometimes called “stones”) can be the source of spontaneous shattering – the stress built into the glass is suddenly released.

If Which? used the information given by commenters in past Convos when new versions or similar topics were presented, I would feel they were more than just a talking shop.

I’ve recently completed a survey for Which? and been contacted by them. My main gripe was that Which? seems not to want to engage with its members – a valuable source of help and information.

Profile photo of wavechange
Member

Patrick – I doubt that many would be interested in technicalities, even though we are. What would be useful would be to know how frequently breakage occurs. My reading suggests that it is infrequent and cuts and burns (because the pieces of broken glass can be hot) are rarely serious. It would be wrong of Which? to ignore the subject and I do hope the claims made in the current magazine are fair and can be substantiated.

For years I used an oven with an inner glass door and a metal outer door. For anyone with children, that might be a good practical compromise between safety and convenience.

Malcolm – In research we made use of fused quartz for various applications where conventional glasses were unsuitable. From your experience in the lighting industry, would fused quartz be economically viable for use in oven door windows? It would certainly be resistant to thermal shock and being made from purer ingredients should avoid the problem of nickel sulphide inclusions.

Profile photo of malcolm r
Member

I doubt that fused quartz would be viable. It is generally used for optical applications. We need to look at the practicalities of this. Toughened glass is successfully used in a huge range of applications and very, very rarely spontaneously breaks. (think car windows and older windscreens for example). Quality of glass and the toughening process are factors of course, and these are covered by both quality and process standards You cannot prevent occasional process faults. I wonder, though, whether some(cheap) brands have less-than-reliable suppliers.

“Technicalities” – or factual information – are important to keep discussions on a sound basis.

Profile photo of wavechange
Member

It would be good if we could ask manufacturers which supplier(s) they use but I would not expect them to tell us. 🙁

Some of us are very keen on having additional technical information available on the Which? website and I’m keen to push for this to happen. I don’t envisage that this is likely to appear in the magazine, though I’m personally keen that the magazine should improve our education.

Profile photo of malcolm r
Member

The European standard (BS EN 60335-2-6), with which cookers must comply, requires the instructions to state that the glass for oven doors and hob covers should not be cleaned with harsh abrasives or sharp scrapers as these may scratch the surface, which may result in shattering of the glass (my words).

Member
Patrick Taylor says:
23 September 2017

“Sunroof shattered while driving in the country, no other cars nearby, nothing overhead, no apparent reason, it just blew up, throwing glass everywhere.” — Driver of a 2013 Volkswagen Jetta in a complaint to NHTSA, as cited in a new lawsuit claiming the carmaker didn’t warn customers that sunroofs may spontaneously explode”
consumerist.com/2017/09/21/vw-drivers-claim-company-didnt-warn-them-that-sunroofs-may-spontaneously-explode/
.

Profile photo of wavechange
Member

I was at a committee meeting in a friend’s house this evening. Our secretary always does some baking before our meetings and tonight mentioned that this evening’s efforts had been produced using a new Neff oven whose door disappears under the oven when opened. That seems like a good way of ensuring that cold dishes are not placed on a hot door and avoid scratching the glass by using it as a shelf.