Wandering Off Topic

[Alfie]

You can buy bin liners that would have enough capacity to hold a body but  I have never come across a large grease proof paper bag.

There was a case (forget the name of the child now) whose dead body was allegedly strapped into a car seat by the father.  Subsequently the car seat was put in a big greaseproof paperbag and that's the reason Grime gave why his dog did not alert to the scent of cadaver dog on it.  You'd have thought they'd have taken the evidence out of the cadaver odour proof paper bag but no.  None too bright these law enforcement types. 

[Mr Gray]

When you put the body in the bag you will contaminate the outside of the bag

[Robittybob1]

When you put the body in the bag you will contaminate the outside of the bag

Contaminate with what?  OK if contamination is a problem hose the bag off before moving it.

[slartibartfast]

When you put the body in the bag you will contaminate the outside of the bag

Assuming the body had reached the required degree of decomposition.

[Robittybob1]

anectdotal..../no scientific evidence to support an unconfirmed alert

We were discussing the chances of an alert being to the past presence of a  cadaver.  You surely can't deny that there was a chance that a cadaver had been in the apartment that night.

[Robittybob1]

Assuming the body had reached the required degree of decomposition.

I think I'd wash it just in case the fresh blood decomposes on the outside of the bag.

[ShiningInLuz]

So if you murder someone "just put them in a sealed plastic bag and you won't get caught out by cadaver dogs".  I don't think so as I'm sure the cadaver odour permeates through a plastic liner/plastic bag.

Cite

[Alfie]

If odour doesn't pass through plastic bags then how does any drug smuggler or terrorist with explosives ever get caught?  &%+((£

[misty]

If odour doesn't pass through plastic bags then how does any drug smuggler or terrorist with explosives ever get caught?  &%+((£

It can be presumed that any object placed inside of an airtight bag at some point contacted the outside of the bag itself leaving traces of the scent present. Dogs, depending upon how well they are trained, can easily detect the smell and alert on the suspicious odour.

Even if the substance inside the bag doesn’t contact the outside, when the bag is sealed the odour can spread around the outside as the air is being removed during the sealing process. This can allow the scent to be imparted upon the outside of the bag and it can be detected there.

Odours are small molecules and in the gas phase they can permeate through polymers. Certain polymers will have specific tolerances for certain gases and something like a polyethylene is pretty good for a lot of things, but not everything. This is really a gas permeability problem.  hte diffusion of gas molecules through a plastic bag is determined in general by the ability of the gas to fit through any porosity available in the polymer chains that make up the bag. Practically, this means that the heavier the molecule, the harder time it may have to diffuse. Furthermore the better the snugness/closeness of the polymer chains to one another (the porosity itself) may play some role.  The chemical attraction between diffusing molecule and plastic bag will play some role!


(As quoted by some clever people in another place)

[Robittybob1]

So if you murder someone "just put them in a sealed plastic bag and you won't get caught out by cadaver dogs".  I don't think so as I'm sure the cadaver odour permeates through a plastic liner/plastic bag.

I have been looking for a cite for this but it isn't a fact that is readily publicised.  I'm sure it is there though.

[Robittybob1]

Thinks Misty and Alfie.
I'm sure that DNA molecules are too large to permeate through plastic bag walls.
Cadaverine and putrescine are small molecules and will leak through plastic. 
I'm sure if a seal pack of meat is left out of refrigeration it will become smelly without the need to open it.
Wikipedia:
Putrescine, or tetramethylenediamine, is a foul-smelling[1] organic chemical compound NH2(CH2)4NH2 (1,4-diaminobutane or butanediamine) that is related to cadaverine; both are produced by the breakdown of amino acids in living and dead organisms and both are toxic in large doses.[2][3] The two compounds are largely responsible for the foul odor of putrefying flesh, but also contribute to the odor of such processes as bad breath and bacterial vaginosis.[4] They are also found in semen and some microalgae, together with related molecules like spermine and spermidine.

Cadaverine is a foul-smelling diamine compound produced by the putrefaction of animal tissue. Cadaverine is a toxic[1] diamine with the formula NH2(CH2)5NH2, which is similar to putrescine. Cadaverine is also known by the names 1,5-pentanediamine and pentamethylenediamine.

[stephen25000]

Thinks Misty and Alfie.
I'm sure that DNA molecules are too large to permeate through plastic bag walls.
Cadaverine and putrescine are small molecules and will leak through plastic. 
I'm sure if a seal pack of meat is left out of refrigeration it will become smelly without the need to open it.
Wikipedia:
Putrescine, or tetramethylenediamine, is a foul-smelling[1] organic chemical compound NH2(CH2)4NH2 (1,4-diaminobutane or butanediamine) that is related to cadaverine; both are produced by the breakdown of amino acids in living and dead organisms and both are toxic in large doses.[2][3] The two compounds are largely responsible for the foul odor of putrefying flesh, but also contribute to the odor of such processes as bad breath and bacterial vaginosis.[4] They are also found in semen and some microalgae, together with related molecules like spermine and spermidine.

Cadaverine is a foul-smelling diamine compound produced by the putrefaction of animal tissue. Cadaverine is a toxic[1] diamine with the formula NH2(CH2)5NH2, which is similar to putrescine. Cadaverine is also known by the names 1,5-pentanediamine and pentamethylenediamine.

I feel sure that Misty can advise you on Graham's Law of Diffusion.

[Robittybob1]

I feel sure that Misty can advise you on Graham's Law of Diffusion.

Graham's law of effusion (sometimes called Graham's law of diffusion) was formulated by Scottish physical chemist Thomas Graham in 1848. Graham found experimentally that the rate of effusion of a gas is inversely proportional to the square root of the mass of its particles.

What is effusion?
Effusion is the process in which a gas escapes through a hole of diameter considerably smaller than the mean free path of the molecules.[1] Under these conditions, essentially all molecules which arrive at the hole continue and pass through the hole, since collisions between molecules in the region of the hole are negligible.

I'm not sure if there are these holes in a plastic body bag.

[stephen25000]

' 'HIDING IN PLAIN SIGHT' Madeleine McCann could be ‘living with her captor and not even realise she was snatched’, says top cop once in charge of investigation

Maddie, who would now be a teenager, might not even realise she was snatched

By Tracey Kandohla '

https://www.thesun.co.uk/news/3292563/madeleine-mccann-with-captor-says-top-cop/

So typeth Tracey, close friend of Kate Mccann.

[Miss Taken Identity]

' 'HIDING IN PLAIN SIGHT' Madeleine McCann could be ‘living with her captor and not even realise she was snatched’, says top cop once in charge of investigation

Maddie, who would now be a teenager, might not even realise she was snatched

By Tracey Kandohla '

https://www.thesun.co.uk/news/3292563/madeleine-mccann-with-captor-says-top-cop/

So typeth Tracey, close friend of Kate Mccann.

Fan  tastic  story. That is what it is fantastic. A little girl as smart as Madeleine doesn't know who she is?  like seriously hahahahaahaha.