REPTILE HEAT MAT DANGERS - Thermal Blocking

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REPTILE HEAT MAT DANGERS - Thermal Blocking

Postby Tortoise Trust » Mon Feb 17, 2014 11:07 am

This is an abridged version of full report that is being published separately. It clearly illustrates the potentially extreme risks of using base, or under-tank heat mats. The heat mat used here was only 23 Watts.

General setup

An 80cm X 40cm vivarium tank was used for this test, sold as "suitable for bearded dragons, iguanas, tortoises and snakes". The heat mat was installed externally, with the heat pat in contact with the base under 1/3 of the unit and Zoo Med 'Aspen Snake Bedding' added as directed on the packaging to a depth of 5cm (2").

Image


Experimental setup

Temperatures directly above the tank base were recorded with a mini-data logger, and a second logger recorded temperatures and humidity at the surface of the substrate. Infra-red thermographs were taken using Fluke and Testo (high resolution) thermal imaging cameras. The test began with the lid of the vivarium in place (with approximately 20% ventilation) and was later removed for comparison approximately half-way through the trial. The room ambient temperature throughout was 20C and RH 48%.

Image

Lateral IR view with tank lid in place. Note how the 'hot' area is highly restricted and there is little thermal penetration through the substrate. In effect, the substrate is acting as a very effective insulator above the heater.

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Results of temperature and humidity logger placed directly on the base of the vivarium. Peak temperatures in excess of 60C were recorded (140 degrees Fahrenheit). These are far in excess of temperatures that are accepted as capable of resulting in severe deep tissue burns to reptiles. As the temperature rose, moisture was driven out of the substrate.

Image

Infra-red image of the substrate directly over the heat pad.

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Temperature and humidity data from substrate surface. Before the lid was removed, RH rose to 100% within the unit. Upon removal of the lid, at 2.00 pm it fell rapidly. Surface temperatures were not greatly affected by the presence of absence of the tank lid, however. Surface temperatures remained, for the most part, between 31-33 C.

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Immediately the substrate is disturbed, however, the dangerous temperatures that exist below the substrate become evident.

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Tests with a proportional control thermostat revealed that in order to prevent dangerous temperatures developing, the probe needed to be in direct contact with the vivarium base, and secured in such a manner that thermal contact was closely maintained. If the thermostat probe was moved only slightly, and thermal contact interrupted, temperatures immediately began to rise to dangerous levels. Use of a thermostat (or thermometer) on the substrate or on the vivarium wall produced completely misleading results, indicating safe temperatures even when temperatures of 60C and more were actually present within the substrate.

CONCLUSIONS & RECOMMENDATIONS


Use of a base-mounted heat pad without a thermostat is extremely dangerous. Even with a thermostat, probe position and security of fixing is critical to safety. Unfortunately, even if safe temperatures are maintained on the base, use of a substrate will result in sufficient thermal blocking effects to prevent useful surface heating.

Substrate type is important. Some substrates transmit heat poorly, and these are the worst possible type to use in conjunction with base-mounted heat pads. Examples include all types of fibres (duvets are made using fibre-based stuffing for a good reason). The typical aspen, coir and hemp substrates frequently sold as "pet" or "reptile" bedding should never be used in conjunction with base heaters of any kind.

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These results reinforce our view that the use of base-heat pads or mats is potentially extremely dangerous, and that their function (if used safely) is compromised. We therefore recommend avoiding their use entirely in this role. They may be used more safely in certain limited circumstances:

1) As a vertical, wall mounted heater;
2) As a base heater with a sensitive thermostat and without any substrate that 'traps' heat. A thin layer of newspaper, for example. Even then, it should be realised that the moment a reptile rests on the surface, thermal blocking and heat build-up will inevitably occur. Such use must therefore be under extreme caution and under strictly controlled and closely monitored conditions. For routine use WE DO NOT RECOMMEND BASE HEATING HEAT PADS OR MATS OF ANY KIND.
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Re: REPTILE HEAT MAT DANGERS - Thermal Blocking

Postby FLINTUS » Tue Feb 18, 2014 8:32 am

A nice report that would be useful to the general tortoise keepers. But how many of the people who will read this on the forum-and even the ones that will have done their research and stumbled upon your website- will use aspen? I 100% agree with your conclusion, but it feels that aspen is a bit of a 'cheat' to publish a little of the report in advance. And 2 inches is not what most would use either, even the 'impulse-buy' keepers. I presume you'll also be testing it with 2ft of soil as well and see how that turns out?
Again, I completely agree with your conclusion and a study into this is needed for less knowledgeable keepers, but I feel as a 'hint of what's to come' you could've chosen a more useful substrate.
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Re: REPTILE HEAT MAT DANGERS - Thermal Blocking

Postby Tortoise Trust » Tue Feb 18, 2014 9:48 am

We actually used the "No 1 preferred snake bedding by professional herpetoculturalists worldwide" (quote) which is available just about everywhere and is also expressly sold (quote) as "can also be used for birds, lizards, tortoises, turtles, tarantulas and insects". This substrate is regularly recommended to tortoise keepers.

It was installed and used precisely as directed in the supplied instructions. This is what many would rely on:

"Spread evenly over the entire bottom of the terrarium for a minimum 2" (5cm) depth. With very large/heavy snakes you may need up to 4" (10cm depth)"


This is not about what a very well informed keeper might do. A very well informed keeper would be unlikely to use it in the first place... or to rely on heat mats like that, it is about educating new keepers to the dangers that exist.

I can tell you exactly what happens with 2" (not 2 feet, for obvious reasons) of sand/soil substrate, because that has been tested too.

1) There is still a thermal blocking effect, through its overall conductivity is much higher than these light-weight fibrous substrates so more heat is removed from the mat or pad, drastically reducing the maximum temperatures achieved in close proximity to the element. It is still possible, in some circumstances, for dangerous temperatures to build up, however.

2) At the same time, the additional mass (and increased conductivity) means that the overall effectiveness is poor.

The conclusion is the same. Not very effective and potentially capable of causing thermal trauma.
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Re: REPTILE HEAT MAT DANGERS - Thermal Blocking

Postby Stuart » Tue Feb 18, 2014 10:49 am

FLINTUS wrote: I presume you'll also be testing it with 2ft of soil as well and see how that turns out?


And what would the point of that be, Flintus?

Who puts 2 feet of soil into a tortoise table, (or thinks of burying a heat mat in the garden at that depth)?

I'm guessing that anyone who knows enough about tortoises to know that they like to dig down from time to time, and so provides them with a decent depth of natural-ish substrate, will know a) not to use aspen or any other of the silly commercially produced substrates that encourage people to think that a tortoise is just like a hamster and b)that a tortoise's preferred method of warming up is from overhead heat sources. So they wouldn't be using a heat mat on the bottom of the enclosure in the first place.

But as for others...
And 2 inches is not what most would use either, even the 'impulse-buy' keepers.

How do you know?
Perhaps you aren't aware of just how incredibly ignorant an awful lot of people actually are (and that includes those who run, or serve in, many pet shops).
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Re: REPTILE HEAT MAT DANGERS - Thermal Blocking

Postby Tortoise Trust » Tue Feb 18, 2014 11:03 am

We tested this because we were contacted by someone who purchased it from a pet shop, used it with a heat pad purchased at the same time, followed the directions on the pack (and as repeated by the pet shop staff), and within 3 weeks found their tortoise almost unable to move. It had (according to the vet) severe burns to the underside of all four limbs. I am trying to find out what the final outcome was.... and obtain photos if possible.
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Re: REPTILE HEAT MAT DANGERS - Thermal Blocking

Postby FLINTUS » Wed Feb 19, 2014 3:22 pm

Just saying I suspect the vast majority of tortoise keepers will not use 2 inches of aspen as their substrate. I have seen a few old care sheets recommend it, but not very many new ones.
The reason I suggested trying it with a decent depth of soil is to see what the actual effect would be in the enclosures of the keepers on here.
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Re: REPTILE HEAT MAT DANGERS - Thermal Blocking

Postby Stuart » Wed Feb 19, 2014 4:06 pm

FLINTUS wrote:The reason I suggested trying it with a decent depth of soil is to see what the actual effect would be in the enclosures of the keepers on here.


OK, but originally you said:
FLINTUS wrote:I presume you'll also be testing it with 2ft of soil as well and see how that turns out?


which was, you must admit, a bit over the top (well, 2 feet over the top, to be precise :lol: )

Anyway, it seems Andy did test the effects of using a heat mat under sandy soil as well as under aspen.

Also, as I've already suggested, it's likely that most keepers on here already know not to use a heat mat under a tortoise anyway.
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