The other day, we notice a terrible burning smell coming out of the server room. Long story short, it ended up being one of the battery modules that was burning up in the UPS unit, but it took a good couple of hours before we were able to figure it out. The main reason we were able to figure it out is that the UPS display finally showed that the module needed to be replaced.

Here was the problem: the whole room was filled with the smell. Doing a sniff test was very difficult because the smell had infiltrated everything (not to mention it made us light headed). We almost mistakenly took our production database server down because it's where the smell was the strongest. The vitals appeared to be ok (CPU temps showed 60 degrees C, and fan speeds ok), but we weren't sure. It just so happened that the battery module that burnt up was about the same height as the server on the rack and only 3 ft away. Had this been a real emergency, we would have failed miserably.

Realistically, the chances that actual server hardware is burning up is a fairly rare occurrence and most of the time we'll be looking at the UPS the culprit. But with several racks with several pieces of equipment, it can quickly become a guessing game. How does one quickly and accurately determine what piece of equipment is actually burning up? I realize this question is highly dependent on the environment variables such as room size, ventilation, location, etc, but any input would be appreciated.

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    @DeerHunter Well thank you goodness it was the end of the day and there were very few people in the builing. Thank you for your constructive criticism, and I'll be sure to let my supervisor know what lives she risked in deciding to keep the system up. Apr 4, 2013 at 19:04
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    @hydroparadise - somebody has to have the guts to say "STOP We are not doing this thing right". If your supervisor doesn't understand safety rules, there's not really much that can be done, except growing some spine and not bowing to the urge to cut corners. Apr 4, 2013 at 19:23
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    @DeerHunter: What would be the appropriate response when you smell something burning? There's no visible smoke, just a burnt smell. Do you turn off the entire datacenter, vent it out for a few hours, then turn on servers one by one until the smell returns? A small 25 rack datacenter could have 1,000 servers to check on, that's a lot of downtime for a "smell" -- the OP didn't report visible smoke or fire.
    – Johnny
    Apr 4, 2013 at 19:43
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    @Johnny - Quoting the OP: "the whole room was filled with the smell. Doing a sniff test was very difficult because the smell had infiltrated everything (not to mention it made us light headed)" Answering your question - yes, you have to vent the room, and troubleshoot systematically. Anything else is irresponsible. Apr 4, 2013 at 19:51
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    So, are those critical of the OP's handling of the smell suggesting that there is no difference in urgency between a smell and a fire/smoke? If you smell something burning in your house but see no smoke and hear no alarm, do you rush you and your family out of the house and call 911?
    – trpt4him
    Apr 11, 2013 at 0:49

7 Answers 7


The general consensus seems to be that the answer to your question comes in two parts:

How do we find the source of the funny burning smell?

You've got the "How" pretty well nailed down:

  • The "Sniff Test"
  • Look for visible smoke/haze
  • Walk the room with a thermal (IR) camera to find hot spots
  • Check monitoring and device panels for alerts

You can improve your chances of finding the problem quickly in a number of ways - improved monitoring is often the easiest. Some questions to ask:

  • Do you get temperature and other health alerts from your equipment?
  • Are your UPS systems reporting faults to your monitoring system?
  • Do you get current-draw alarms from your power distribution equipment?
  • Are the room smoke detectors reporting to the monitoring system? (and can they?)

When should we troubleshoot versus hitting the Big Red Switch?

This is a more interesting question.
Hitting the big red switch can cost your company a huge amount of money in a hurry: Clean agent releases can be into the tens of thousands of dollars, and the outage / recovery costs after an emergency power off (EPO, "dropping the room") can be devastating.
You do not want to drop a datacenter because a capacitor in a power supply popped and made the room smell.

Conversely, a fire in a server room can cost your company its data/equipment, and more importantly your staff's lives.
Troubleshooting "that funny burning smell" should never take precedence over safety, so it's important to have some clear rules about troubleshooting "pre-fire" conditions.

The guidelines that follow are my personal limitations that I apply in absence of (or in addition to) any other clearly defined procedure/rules - they've served me well and they may help you, but they could just as easily get me killed or fired tomorrow, so apply them at your own risk.

  1. If you see smoke or fire, drop the room
    This should go without saying but let's say it anyway: If there is an active fire (or smoke indicating that there soon will be) you evacuate the room, cut the power, and discharge the fire suppression system.
    Exceptions may exist (exercise some common sense), but this is almost always the correct action.

  2. If you're proceeding to troubleshoot, always have at least one other person involved
    This is for two reasons. First, you do not want to be wandering around in a datacenter and all of a sudden have a rack go up in the row you're walking down and nobody knows you're there. Second, the other person is your sanity check on troubleshooting versus dropping the room, and should you make the call to hit the Big Red Switch you have the benefit of having a second person concur with the decision (helps to avoid the career-limiting aspects of such a decision if someone questions it later).

  3. Exercise prudent safety measures while troubleshooting
    Make sure you always have an escape path (an open end of a row and a clear path to an exit).
    Keep someone stationed at the EPO / fire suppression release.
    Carry a fire extinguisher with you (Halon or other clean-agent, please).
    Remember rule #1 above.
    When in doubt, leave the room. Take care about your breathing: use a respirator or an oxygen mask. This might save your health in case of chemical fire.

  4. Set a limit and stick to it
    More accurately, set two limits:

    • Condition ("How much worse will I let this get?"), and
    • Time ("How long will I keep trying to find the problem before its too risky?").

    The limits you set can also be used to let your team begin an orderly shutdown of the affected area, so when you DO pull power you're not crashing a bunch of active machines, and your recovery time will be much shorter, but remember that if the orderly shutdown is taking too long you may have to let a few systems crash in the name of safety.

  5. Trust your gut
    If you are concerned about safety at any time, call the troubleshooting off and clear the room.
    You may or may not drop the room based on a gut feeling, but regrouping outside the room in (relative) safety is prudent.

If there isn't imminent danger you may elect bring in the local fire department before taking any drastic actions like an EPO or clean-agent release. (They may tell you to do so anyway: Their mandate is to protect people, then property, but they're obviously the experts in dealing with fires so you should do what they say!)

We've addressed this in comments, but it may as well get summarized in an answer too -- @DeerHunter, @Chris, @Sirex, and many others contributed to the discussion

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    University I went to installed a new data center. They implemented a highly sophisticated EPO/Fire Suppression system. The equipment it was protecting was in the millions of dollars and it was also being used for millions of dollars of research for the medical part of the school. Obviously if it was needed the red button would be hit but, that being said if the red button was hit, just resetting it was close to $200,000 US dollars. Tax Payer Dollars you can sure as hell bet that if the switch was hit when it wasn't needed the guy who hit it would no longer have a job.
    – Ryan
    Apr 4, 2013 at 23:14
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    +1 for the buddy system. I think it's a little nuts that there are DCs out there that use the EPO to also dump fire suppression as well. There are plenty of situations where you'd want to EPO without wanting to dump halotron all over the guy getting electrocuted. An EPO is a serious deal but isn't a "destroy everything in the DC kinda deal" or at least shouldn't be. The guys in the DC should hopefully understand the big red button and the fire suppression system well enough to weigh the effect of hitting the button. An EPO may actually stop a fire and save the DC, for instance.
    – chris
    Apr 5, 2013 at 3:00
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    An important note I haven't seen mentioned is that the majority of the time when something fails so as to give off a burning smell, whatever is burning will extinguish itself before the odor is detected and without burning anything outside the failed equipment. Sometimes a piece of equipment will continue to smoulder as long as it has power, but if one sees smoke it should be possible to identify the equipment, cut power just to it, and see whether the smoke soon clears or continually gets worse.
    – supercat
    Apr 5, 2013 at 16:21
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    @ryan: If hitting the big red button costs so many tax payer dollars, the responsible person has hopefully worked out a plan to resolve minor incidents with the local fire department that doesn't involve endangering employees.
    – Christoph
    Apr 6, 2013 at 8:59
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    @ryan That reminds me of a tv report about CERN that I saw recently: The camera team and reporter were taken really to the guts of the system and and one moment one of the camera guys almost rammed a red emergency off button with his backpack - giving near heart attacks to the staff guy thinking about the reboot costs ... Apr 3, 2016 at 10:45

A Thermal Imaging Camera could do the work, and let you identify where the overheating is. A device like this would let you identify also the origin of a fire or burning in a smoke filled room.

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    Thermal cameras go for under a grand nowadays, and if you are running a big server room they are a tool well worth to have. Apr 4, 2013 at 15:18
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    A T.I.C. is not so expensive and is very useful in a datacenter or big server room. Not only in case of problems like overheated cables or equipment, but also as a preventive or early detection of issue, refrigeration optimization, air flow, etc.
    – ddalcero
    Apr 4, 2013 at 15:19
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    A laser temperature gun, like this one, is a cheap alternative
    – House
    Apr 4, 2013 at 16:40
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    @mfinni Electricians also often have thermal cameras. (A thermal imaging check of our power distribution panels every year, or after any major wiring work, was standard when I worked at a hosting company).
    – voretaq7
    Apr 4, 2013 at 19:58
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    A thermal camera has very large limitations: 1. The field of view may prevent the usage 2. Your environment may be very dense. [Big fires will be spotted but not small ones] 3. Averaging of temperatures will be needed to determine a threshold
    – monksy
    Apr 5, 2013 at 15:43

You do none of these things that have been said. You leave the hazardous environment because whatever is being pumped through the entire room is dangerous to your health and may really mess up your lungs. If there is an acrid smell of something burning in the room that you can't find, call (911|112|999|whatever emergency number fits your jurisdiction) and let the fire (company|department|brigade) sort it out while they're on bottled air.

Computer parts contain all sorts of interesting chemicals including mercury, cadmium, lead, and lots of plastics in casings. Notice that all the links I made explain how low level exposures can cause lasting damage or even quick death. This is an environment that can be immediately dangerous to life and health.

... so really, if something is burning, don't spend hours sniffing the fumes. If you can't identify it and immediately act to contain it, get out.

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    It should be added that if this happened in a "real" datacenter with smoke detectors integrated with the air conditioning and an extinguishing system installed, the fire alarms would have went off and the room would be sealed and flooded with Argon or CO2 automatically, so there could not even be a thought about running around and sniffing equipment.
    – the-wabbit
    Apr 5, 2013 at 7:22
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    @syneticon-dj This depends on the type of detectors installed. Ionization detectors might have tripped the fire suppression, but I've worked in (and currently host equipment at) places that have optical smoke detectors - Those require visible smoke (or at least a good haze) before they trip.
    – voretaq7
    Apr 5, 2013 at 15:57
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    I wish I could upvote this more. at the risk of being controversial, 'get a professional' firefighter is the only way forward.
    – user9517
    Apr 6, 2013 at 17:14
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    Yeah, as a former firefighter, I wouldn't stay there without my gear. Even when a fire is out, we are trained to stay packed up because of the poisonous gasses. If I would call the pros, you should too! Apr 6, 2013 at 17:50
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    @Michael the designs I've seen did not rely on ceiling smoke detectors but had photoelectric detectors in the return air flow. The only time I have seen it trigger was during a testing routine where the argonite system has been detached and a smoke source has been placed in one of the closets. It worked as I would expect it to work. Thankfully, I never had to deal with real fires.
    – the-wabbit
    Oct 13, 2016 at 7:37

If you had proper monitoring on the UPS (usually via SNMP), the unit itself should have rung the bells on your monitoring system. If it didn't, talk to your vendor about that. It either malfunctioned or your monitoring system isn't properly configured.

If something active is actually burning, it should be complaining about it in some way, or simply be off the network, which should also cause an alarm.

If it's something like an actual power rail burning through insulation, and it's not on a smart PDU, then we're back to your original question, which is "how do I find a burning thing?" And I think the proper answer is "Hit the EPO and figure it out. Your production servers are probably not important enough to go risking lives."

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    What does EPO mean?
    – Midhat
    Apr 4, 2013 at 15:10
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    Emergency Power Off...the big red button that cuts all power to the room. Mostly for when its on fire.
    – Grant
    Apr 4, 2013 at 15:15
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    An emphatic +1, would have voted +1,000. Hit the button, evacuate, wait, sort out things later. Doing business as usual with fire and smoke present (and trying to troubleshoot anything) is one of the worst mistakes an engineer can make. Apr 4, 2013 at 18:20
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    @chris I have to respectfully disagree on "EPO, Leave, Wait" -- Activating the EPO and/or clean agent release for a room full of production gear can very often be what we like to call a Career Limiting Move. If there is not an active, visible fire or trail of smoke coming from some equipment performing some initial investigation is usually the Right Thing. Of course you should absolutely be prepared to bolt from the room while hitting the appropriate red buttons at any point in your investigation.
    – voretaq7
    Apr 4, 2013 at 19:52
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    It's likely even a perfect monitoring system would not have caught this until the same moment the UPS panel said "Replace Module" -- that being said you certainly want your monitoring system to bring such things to your attention. Next time a module may fail at 19:30 on a Friday when nobody's around, and the monitoring alert will get you to come back in and deal with the problem before it develops into a fully-fledged emergency. If you can tie monitoring into your FACP your smoke and/or heat sensors may even warn you about insulation burning off power rails and the like.
    – voretaq7
    Apr 4, 2013 at 19:55

This is one of those situations where

XKCD Die Hard sysadmin

doesn't apply, you should call a professional

Firefighter in protective gear

Anything else is just plain stupid.

  • @Navin No you don't the guys in the fire department do that.
    – user9517
    Apr 4, 2016 at 9:32
  • Some comment were deleted there, but like it's told, the answer is direct, but if something is burning, as you can get intoxiced by the fume, or any other accidents. Dont try to go in to find what is burning as it's dangerous, especialy in isolated server room.
    – yagmoth555
    Jan 6, 2020 at 17:52

As someone whose former career was as an electronic tech, I have experience with "burning smells" that were not fires. This isn't uncommon.

I wouldn't shut down a data center for a smell. Smoke is another matter, something is really burning (usually, but a pea-sized tantalum capacitor can fill a room with smoke too). It's amazing how much smell a fried component in a power supply can make.

A TIC or IR thermometer (a useful tool and a lot cheaper than a TIC) would not necessarily show it as the component doesn't generate much heat at all and it's inside a case. But check for devices not working, use you monitoring tools. For a smell like that then 95% of the time it'll be a power supply affecting the performance of the whole device.

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    +1, blown power supplies are common. In most datacenters with high airflow rates the smoke is blown away quickly and it is difficult to locate the source of the smell. In a small room however, the smell can be pretty bad, and can quickly spread throughout the entire room. Apr 10, 2013 at 20:15

I like the IR imaging or thermometer answers but maybe what would also help is a real "odor detector". After all what triggered your caution was the smell. Smoke, heat, IR etc. are all surrogates.

Something like this one: from Shinyei . I've personally never used them or even seen them used in a datacenter. But at least theoritically it should be a neat tool. If you have the money to spend on this gizmo that is.

http://www.sca-shinyei.com/odormeter or http://www.intopsys.com/products/cyranose.html?gclid=CNXXzOrLs7YCFUws6wodViYApQ

It gives you an odor strength as well as classification. So homing in onto the odor should be possible. Devil's in the details of course. How sensitive it is, masking out spurious background odor etc.

One advantage over purely temperature based measurements is that often odor occurs at a far earlier point or threshold. Or if the overheated component is hidden by a body / concealed wiring etc. it is easier to detect molecules escaping than a line-of-sight hot spot.

Another situation is a non-heat related smell. We've had a cooling circuit leak before and the coolant smells were peculiar too. I won't even go into the now ancient case of a rodent dead in the ducts. :)

I was surprised how sensitive these sensors are. Apparantly H2S / mercaptans etc. (usual culprits) are detectable at sub ppm levels.

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