Following is an
overview of the 1998 UK Limerick Report regarding the toxic
gas theory for cot death (the Richardson hypothesis).
Contrary to publicity, the Report did not disprove the
theory - in fact, it provides further confirmation of it.
At the end of 1994
the British Government faced huge potential legal claims by
bereaved parents. In the 1980s the Government had required
manufacturers to include a fire retardant in cot mattresses,
and had approved antimony trioxide for the purpose. The
result was the generation within cot mattresses of stibine
gas, which caused thousands of cot deaths. If the Limerick
Report had supported the toxic gas theory for cot death, the
British Government would have been liable for millions of
pounds in damages.
did the Limerick Committee investigate?
whether certain toxic gases are generated from fire
retardant chemicals contained in PVC-covered cot mattresses.
Was this a full investigation of the
toxic gas theory for cot death?
No. It had serious
The Committee did
not investigate any mattresses other than those covered with
PVC. They did not investigate natural products used as
bedding (despite the fact that many cot deaths occur on such
materials, e.g. sheepskins). They focused on only one of the
three relevant gases (stibine).
the Limerick Report relevant in New Zealand?
Largely, no. This is
because PVC-covered mattresses are very rarely used in New
Zealand. Sheepskins (which are frequently used as baby
bedding in New Zealand) were specifically excluded from the
study. New Zealand mattresses very rarely contain fire
retardants. The toxic gases most likely to be generated from
New Zealand baby bedding (phosphines and arsines) were not
focused on in the study.
then does the Report provide confirmation of the toxic gas
It confirms (yet
again) the gas generation which causes cot death: the
Committee achieved generation of a form of stibine. Other
researchers had already proved the generation of all three
gases: phosphines from phosphorus, arsines from arsenic and
stibines from antimony.
the Report's conclusion states that the toxic gas theory is
Committee had replicated the toxic gas generation, they said
such gas was not the cause of cot death. This conclusion was
based on a large number of errors and irrelevancies. For
The Report stated
that one particular fungus which can cause gas generation
(S. brevicaulis) was not found on any mattresses on which
babies had died of cot death. Irrelevant. The Committee
found S. brevicaulis and many other micro-organisms on cot
mattresses - and a number of these are capable of generating
toxic gas if phosphorus, arsenic or antimony are present in
a mattress. Whether babies had died on the mattresses tested
by the Committee is immaterial.
become established in nearly every mattress which is slept
on, and in underbedding which is washed infrequently.
The Report stated that what Richardson
had identified as a fungus was actually bacteria.
Bacteria as well as fungi can generate toxic gas from the
The Report stated that while toxic gas
was produced under laboratory conditions, no gas could be
produced in cot conditions.
Irrelevant. Gas generation has already been achieved
in cot conditions, and failure by the Limerick Committee to
do so doesn't negate this fact.
have found it difficult to achieve gas generation
consistently using media with a neutral pH. But the pH of a
cot mattress is often higher, owing to the conversion of
urea to ammonia. Experiments carried out using high pH (say,
10) have achieved more consistent gas generation. In these
tests fungus flourished and the amount of gas produced was
greater than at neutral pH.
The Report stated that cot death
babies did not show the typical physiological effects of
phosphine, arsine or stibine poisoning, e.g. haemolysis and
pulmonary oedema. Of course
they didn't. Babies die so quickly from this type of
poisoning that these effects don't have time to develop.
example, takes many hours to develop; so does pulmonary
oedema. But this gaseous poisoning can kill a baby within
data contained in the Report relates to adults and older
children. None of it relates to babies - and it is well
known that babies' blood and physiological responses differ
materially from those of older children and adults.
The Report stated that cot death
babies had the same amount of antimony in their body tissue
as babies who had died of other causes.
Wrong. Research carried out in 1994 showed that post
mortem body tissue of cot death babies contained many times
more antimony than tissue of babies who had died of other
The Report stated that antimony
present in the tissue of cot death babies could have come
from many sources other than their mattresses.
Wrong. The same 1994 research
showed that the body tissue of babies who had died of causes
other than cot death contained no detectable antimony (or in
one case very little). If the Report were correct, there
would have been similar amounts of antimony in the tissue of
all the babies tested, whether they had died of crib death
or of other causes.
The Report stated that the
introduction of antimony and phosphorus into mattresses in
Britain did not coincide with a rise in the cot death rate.
Wrong. These chemicals were
first introduced into cot mattresses in the early 1950s, and
the British cot death rate increased steadily from that time
onwards. (In fact the term "cot death" was coined in 1954 as
a result of the marked increase in the number of such
The highest cot
death rate in Britain (2.3 deaths per 1000 live births in
1986-1988) coincided with the highest concentration of
antimony in cot mattresses. The British Government had
required a fire retardant to be incorporated in cot
mattresses by 1988. Manufacturers were given four years'
warning and during this period moved towards compliance with
the new standard.
The Report stated that the steepest
fall in cot deaths in Britain occurred when antimony was
very prevalent in cot mattresses and coincided with the
"Back to Sleep" campaign.
Highly misleading. Certainly the British cot death
rate fell while the amount of antimony in mattresses was
high - but that was because from mid-1989 onwards parents
took preventive measures against toxic gas generated in
their babies' mattresses. Furthermore, manufacturers began
to remove antimony from mattresses.
In June 1989 the
toxic gas theory was publicized nationwide and the crib
death rate immediately began to fall (see graph). It had
fallen 38 % (to about 1.4 deaths per 1000 live births) by
the time "Back to Sleep" was launched in December 1991 -
two-and-a-half years later. The fall was steepest following
the commencement of "Back to Sleep" because that campaign
added to the success already being achieved by advice based
on the toxic gas theory.
about the claim in the Report that three babies have died of
crib death on polythene-wrapped mattresses?
This claim is unsubstantiated.
The types and thicknesses of the plastic are not known. Was
it thick, clear polythene (safe) or thin or coloured
polythene (unsafe)? Was there bedding containing phosphorus,
arsenic or antimony on top of the plastic? Were sheepskins
used? Or mattress protectors? These questions have not been
answered, and without this information the claim is not
In February 2000 Dr
Peter Fleming, a co-author of the Limerick Report, stated
that the claim that three babies had died of crib death on
polythene-covered mattresses could not be substantiated.
Are there other
findings which support the toxic gas theory?
Yes. For example:
has proved that the crib death rate rises as mattresses are
re-used from one baby to the next. This is because
micro-organisms become better established in a mattress as
it is used. When re-use commences, toxic gas is generated
sooner and in greater volume. Statistics show that the cot
death rate jumps from first babies to second babies; and
jumps again from second babies to third babies; and rises
still further for later babies. The reason is that parents
frequently buy a new mattress for their first baby and then
re-use it for subsequent babies. Research in the USA has
reported that cot death babies show neurochemical deficits
relating to heart function and breathing. This is accounted
for by the fact that phosphines, arsines and stibines are
all "nerve gases". They shut down the central nervous
system, causing cessation of heart and breathing functions.
(This is why crib death babies do not show any apparent
of the Limerick Report should be disregarded. Other
researchers have disproved them; and so has the practical
experience of mattress-wrapping in New Zealand. Since late
1994 many tens of thousands of New Zealand parents have
wrapped their babies' mattresses for cot death prevention,
and since that time the New Zealand crib death rate has
fallen markedly. The practical experience of
mattress-wrapping proves the toxic gas theory for crib
death. If mattress-wrapping did not prevent crib death, many
deaths would have occurred by now on polythene-wrapped
THERE HAS NOT BEEN
ONE REPORTED CRIB DEATH ON A
BabeSafe MATTRESS COVER OR