Surface temperature for insulation design 2

[athomas236]

Can anyone advise what should be the maximum surface temperature to prevent skin burns.

I have seen different values over the years and would like to know the current thinking.

At the moment I am thinking about designing insulation for personnel protection using max temperatures of 55C for metallic surfaces and 60C for non-metallic surfaces.

These temperatures to be calculated for zero wind speed, with an ambient shade selected so there is an 80% probability of it not being exceeded or 35C whichever is the lowest. This is because the maximum ambient shade temperature is 52C.

Thanks for any advice

athomas236

 

[codeeng]

60C is our standard for personnel protection. Process Industry Practices (PIP's) has an excellent spec for insulation.

 

[athomas236]

Thank you for your assistance, much appreciated.

Regards,

athomas236

 

[IRstuff]

Bear in mind that lower temperatures than 60º can still cause burns if exposure time is sufficiently long.

There should also be warning labels to that effect.

TTFN

 

[MortenA]

On the other hand - 60 deg C is pretty comservative. You wont get a burn unless you are forced to hold on to the item for som time. Just touching the pipe by accident being able to withdraw the hand/arm whatever will cause some pain but bot a burn (IMHO).

Best regards

Morten

 

[athomas236]

MortenA

What is meant by IMHO

Regards,

athomas236

 

[DSB123]

athomas236,
The British Standard for Insulation specifies 55 Deg C for surface temperature limit.

 

[quark]

60[sup]0[/sup]C should be OK and this is what we maintain.

Refer

http://www.cheresources.com/insulationzz.shtml

under Safety

IMHO - In My Humble Opinion.

 

[athomas236]

DSB123,

Can you tell me which BS because I have looked at the BS5970 and found nothing.

Quark,
Thank you for your assistance, the link goes a useful page.

Regards,

athomas236

 

[moltenmetal]

IMHO = "in my humble (honest) opinion"

It greatly matters whether the insulation is clad or not.

Metal insulation cladding should be kept below 60 C to prevent burns. But surface temperatures for unclad, low-conductivity insulations can be considerably hotter without causing burns. A burn is caused when sufficient heat is transferred to the skin to cause the burn. A low thermal conductivity, low heat capacity surface can be hotter without burning than a metallic surface (which has both a higher thermal conductivity and heat capacity).

 

[IRstuff]

You cannot only consider simple touching burns.

If someone falls or trips and winds up stopping their fall with their hand, they won't be able to quickly remove their hand. The contact time could significantly increase and even 55ºC might be too high.

You need to do a thorough safety analysis.

TTFN

 

[athomas236]

In BS 5422 2001 there are three tables that can be used for selecting insulation for personnel protection. Deatils of these tables are:

Table Surface Surface
emissivity temperature C
16 0.90 (non metallic) 59
17 0.05 (bright aluminium) 50
18 0.90 (non metallic) 50

If I was using this standard, I would use tables 16 and 17 for cost reasons.

Regards,

athomas236

 

[unclesyd]

One thing not mentioned is the location of the insulated component.
In our case the process runs at temperatures from 200°C-300°C inside a an occupied building and the surface temperature is very relevant to the environmental temperature in the workplace. Not only does the workplace temperature have to be controlled but the usage of the heating media, vaporized oil, has to be considered.
Back in the good old days of asbestos our surface temperature standard was 50°C. This was met with no problem. The lost of asbestos resulted in the change of the surface temperature standard to 59°C. This caused almost immediate problems with the increase in workplace temperatures in some areas to an unacceptable range. There were several problems; not enough vent fans, ambient outside air of 35°C with high humidity and the finite capacity of the process heating source. Because of this the insulation surface temperature max was returned to 50°C or less. This required an increase in the thickness, with a substantial cost of the insulation, form the standard established with Asbestos containing materials. Insulation costs are quite a concern as every piece on each process is different and has to be hand laid up.
In our case the majority of the insulation has to be made removable for a unit overhaul at least once a year. On the few units that were insulated with 59°C surface temperature in mind the handling of the insulation became a problem for the mechanics using the normal PPE. A lot of this insulation instead of being handed off was dropped and destroyed. The small increase in surface temperature required the use of hot gloves and slowed the dismantling of the process piping to point where it became a serious safety concern. Handling of insulating components became a major cost factor with the lost of Asbestos as the normal Calcium Silicate loses most of its strength after a short exposure to 200°C. The process dictates that the piping be dismantled at temperature or allowed to cool to below 185°C. At 185°C the polymer has to be mechanically cut at each flange.

All new insulation on site is now installed with 40°C as standard and the weather covering on any flammable process line be SS. This is SS covering with SS bands. In fact there has been a movement to change the standard covering to SS from AL on all lines.

This is the long way to say that the of a insulation of a particular process or insulation in general should be an engineering exercise taking all things into consideration, not in least the surface temperature required for personnel protection.

Did OSHA ever come out with a requirement for this temperature?

 

[davefitz]

Here in the USA our safety regulations (OSHA) require a surface temp below 140 F in areas that are accessible by workers.

One measure to reduce the insulation requirements needed to get down to 140 F is to use high emissiivity surface treatment ( anodized aluminum or paint with emissivity at e=0.85).

I have seen papers years ago that had shown the required temp to avoid burns is related to the surface's conductivity , as we all know a hot pot with a metal handle is worse than one with a wood handle, but our OSHA rules do not make the distinction.

 

[IRstuff]

This one goes into lots of details. Ends with a complete table of temperature of particular materials vs exposure time. Once you've determined the maximum potential exposure time of skin contact to the hot surface, you can determine the maximum temperature allowable:

http://www.rospa.com/productsafety/articles/temperatures.htm

TTFN

 

[athomas236]

syd, dave and stuff

Thanks for all your advice which as usual is excellent. I should have thought of ROSPA though, especially as I live in the UK.

Best regards,

athomas236

 

[PEHasan]

60 degree C is fine.