carbon monoxide poisoning from blasting operations in construction

carbon monoxide poisoning from blasting operations in construction
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2001 An Earth Odyssey
2001 Odyssée de la Terre
CARBON MONOXIDE POISONING FROM BLASTING OPERATIONS IN
CONSTRUCTION WORKS
AM
IE
&
TA
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Richard Martel, INRS-Géoressources, CGQ, Sainte-Foy, Qc, Canada
Luc Trépanier, INRS-Géoressources, CGQ, Sainte-Foy, Qc, Canada
Louis-Charles Boutin INRS-Géoressources, CGQ, Sainte-Foy, Qc, Canada
Marc-André Lavigne INRS-Géoressources, CGQ, Sainte-Foy, Qc, Canada
Benoît Lévesque, Institut national de Santé Publique du Québec, Québec, Qc, Canada
Guy Sanfaçon, Institut national de Santé Publique du Québec, Québec, Qc, Canada
Pierre Auger, Institut national de Santé Publique du Québec, Beauport, Qc, Canada
Louise Galarneau, Régie régionale de la santé et des services sociaux de l’Estrie, Sherbrooke, Qc, Canada
Patrick Brousseau, Defence Research Establishment Valcartier (DREV), Val-Bélair, Qc, Canada
CH
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ABSTRACT
Explosives used for blasting operations in civil engineering works like construction of piping systems under roads, of pools, of houses
and buildings can generate large volumes of carbon monoxide (CO). Carbon monoxide can represent between 1 to 3% of the gases
produced by usual explosives. The production of 10 to 24 l of CO by kg of explosives blasted is theoretically anticipated. Carbon
monoxide is a gas without neither characteristic colour, smell nor taste and can migrate in the fractured rock of the blasted area on fair
distance and then infiltrate in close spaces like sewage systems, manholes, but also in basements of houses. In Quebec, during the
last 10 years, 7 people were poisoned in their houses to the point that they had to be treated in hyperbaric chambers. In the USA many
accidents occurred and one worker died in a manhole. This paper makes a review of accidents in Québec and looks for the common
factors. It also presents the results of field tests performed to evaluate the behaviour of CO in fractured rock following blasting
operations. These data are critical to modify the way the blasting contractors work to limit the risk of people intoxication and to make
recommendations to regulators on measures to take to avoid this problem.
INTRODUCTION
OD
1.
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RÉSUMÉ
Les explosifs d’usage pour le sautage relié à des travaux de génie civil comme la mise en place de services publics tels que les
réseaux d’aqueduc et d’égout, à la construction de piscines, de résidences ou d’édifices peuvent générer d’importants volumes de
monoxyde de carbone (C0). Le monoxyde de carbone peut représenter de 1 à 3% du volume des gaz générés pour des explosifs
usuels. La production de 10 à 24 l de monoxyde de carbone par kg d’explosif détoné est théoriquement envisageable. Ce gaz est
incolore, inodore et insipide (sans saveur) et peut migrer dans le roc fracturé adjacent à la zone dynamitée sur des distances
appréciables pour ainsi s’infiltrer dans des espaces clos, tels que des égouts, des trous d’homme mais aussi des sous-sols
d’habitations. Au Québec, depuis dix ans, sept personnes ont été intoxiquées dans leur résidence au point de devoir être traitées en
chambre hyperbare. Aux États-Unis plusieurs accidents sont aussi survenus et une personne est décédée dans un trou d’homme. Cet
article fait une revue des incidents survenus au Québec et examine les différents facteurs communs aux incidents. Il présente
également les résultats d’essais de terrain qui étudient le comportement du CO dans le roc fracturé suite à des sautages à l’explosif.
Ces données sont essentielles pour améliorer les pratiques des entrepreneurs en dynamitage afin de limiter les risques d’intoxication
de personnes liés à ce type de travaux et faire des recommandations aux instances réglementaires concernées sur les mesures à
prendre pour éviter d’autres incidents.
AN
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Carbon monoxide is a gas without neither characteristic
colour, smell nor taste. Hence it is not irritating. Because
of these reasons, this gas can not be detected by any
senses. When it is absorbed by the respiratory system,
CO is rapidly transferred in the circulatory system. In the
blood, it develops an affinity with haemoglobin 200 to 250
times higher than oxygen (Meredith and Vale 1998). There
were many CO intoxication cases due to the presence of
an engine or a combustion heating system. Recently, some
authors have written on CO intoxication of people exposed
to emanations produced by the use of explosive devices in
a residential environment (USA : Scranton(Penn) in1988
(Dougherty et al.) NIOSH, 1999; In Canada :Hamilton
(Ont, 1995), Beauport, Qc (Auger et al., 1998).
Santis(2001) made a report of cases in Canada and in
the United States. In the province of Quebec (Canada), 8
cases have been registered during the past 10 years. The
maximum concentration of CO measured in the
contaminated houses reached 1040 ppm. Many people
The International Association of Hydrogeologists
l'Association Internationale des Hydrogéologues
have been indisposed and seven of them had to undergo
treatments in an hyperbaric chamber. In each case where
a disaster has been avoided, the misunderstanding of the
situation and the insidious nature of the intoxication to CO
were the most important factors. These two same factors
added to the important amount of blasting activities, i.e.
between 1000 and 1500 each year in the Province of
Quebec, executed close to residential neighbourhoods
suggests that the registered cases appear only to be the
tip of the iceberg. Consequently, it is believed that these
activities constitute a danger for both workers and people
in general.
This paper relates the CO intoxication cases that
occurred in the Province of Quebec these past years in
houses following blasting activities. Moreover, factors that
favour the infiltration of CO in houses close to the blasting
sites are underlined. Finally, we present the results of an
assessment started in the winter of 2001 which had as a
goal to evaluate at a field scale the production of CO and
to identify the migration mechanisms of CO in fractures
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Based on field observations and data and on results of
our field tests (the next section), probable pathways of
gas migration can be identified for each incident. Broken
underground conduit by blasts, fill around underground
conduits in road trench or house trench or fractured rock
created by blasts between houses or between a house
and a road are the different pathways identified in the
Québec incidents. Materials that surround the foundations
of a house (sand and gravel) constitute also a preferential
zone for gas migration. In summary, gases use pathways
that facilitate their movement, i.e. through zones of high
permeability (joints in rock, in or along underground
conduits…). The number of people intoxicated dropped
from 16 to 0 per incident after July 2000 when a
recommendation to the blast contractors was made by a
provincial comity (MSSS/MENVQ,2001) to put carbon
monoxide detectors in houses located at less than 75 m
from blasts areas.
induced in the rock following the blasting of a house
basement.
Theoretical masses of CO produced per mass
unit of commercial explosives. (adapted from
Katsabanis and Liu, 1996)
Explosives
Theorical volume of CO
produced per mass unit (l/kg)
TA
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1.1 Review of incidents in Québec
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The explosive type used in almost all dynamiting activities
is ANFO mostly because of its low cost. It is a mix of
ammonium nitrate (94.6%) and fuel oil (5.4%).
Sometimes, aluminium is added to increase the power of
the explosives. The ANFO is often found under different
commercial brand names. It depends of the producer and
of its composition. It can be found either in small granules
or under the form of an emulsion in a cartridge. The
ANFO is used in combination with explosives that act as
primer. The composition of these explosives is nitroglycerine and carbon that are fused by a detonator.
Granules of ANFO are used in a borehole where there is
no water in comparison with cartridges of ANFO that are
used when there is water in the borehole. Table 1 lists all
the gases produced in a calorimeter during the
combustion or the detonation of commercial explosives.
Water vapour and nitrogen constitute the major part of
the gases produced. As for the carbon dioxide, it is
present in small amounts. Carbon monoxide represents
1% to 3% of the total volume of gases produced in the
cases of explosives tested. In general, there is 10 l to 24 l
of carbon monoxide produced per kilogram of explosive
detonated.
IE
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Table 2 presents the 8 incidents recorded that occurred
in Québec between 1991 and 2001. All type of works are
related to civil engineering works close to houses. The
distance of houses to the blasting site where incident
occurred varied from 6 to 53 m; the longest distance
being attributed to an underground conduit. In all cases
no excavation was done immediately after the blasts. The
maximum concentration recorded in the houses varied
from 200 to 2000 ppm. The drain pipe box of houses
seems a preferential way of gases infiltration in the
basement. Considering that the produced gas are lighter
than air, they are diluted with the surrounding air and they
are migrating vertically towards higher floors. The density
3
difference is approximately 0.2 kg/m between gases
produced that should be at an average temperature of
3
10°C in the filling close to the foundations (0.97 kg/m )
and the surrounding air in a house at a temperature of
3
25°C (1.18 kg/m ). The type of rock were sedimentary or
metamorphic. In all cases the rock was already fractured
before blasting or could be preferentially fractured along
identified cleavage. Water was present in most tests.
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AM
DYNOTEX
2.
METHODOLOGY
2.1
Localisation of experiments
,J
22,4
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UNIMAX
BLASTEX
The evaluation of carbon monoxide migration was done in
experimental plots located in the same rock formations
where CO intoxication incidents took place in Rock Forest
(20 km west of Sherbrooke) and Beauport (20 km east of
Québec City). The tests were performed in the slate of the
Magog formation in Rock Forest and in the limestone of
the Trenton Group in Beauport. The selection criteria for
the tested areas were based on accessibility of the site,
depth and confinement of the rock formation, water table
depth, and the proximity of houses. The Rock Forest
tests were made on a flat private land located at more
than 125 m from a private building. The confinement of
the rock in the tested area was made by 0.5 to 2.5 m of
clayey till (see figure 1). The water table is located at a
depth of 2 m in the till (perched water table) and at a
depth of 4 m in the rock formation. The Beauport test was
made on a private flat land adjacent to a rock quarry
(Carrière Québec Inc.). The tested area is located at 60
m from the quarry wall and 70 m from the private houses
and a road and is covered by 0.3 to 1m of sand. A
perched water table is in the sand formation at 0.5 m
depth.
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Table 1.
Three blasting tests were performed at Rock Forest
nd
th
between January 22 2001 and March 15 2001 and one
test was done at Beauport between May 31 2001 and
June 6 2001. The size ofthe blast is representative of a
medium-large house of 10 m by 10 m. At Rock Forest,
the first test (HOUSE 1) was made in the middle of the
field (Figure 1). After the first test, a trench of 60 m long
was blasted in the rock to simulate a road with its public
services. Then the HOUSE 2 test was performed. This
house is located beside HOUSE 1 and is connected to
the trench by a small trench (equivalent to private
services entrance). The HOUSE 3 test was made on the
other side of the trench between HOUSE 1 and HOUSE 2
tests. This house was also connected to the trench This
test was made to evaluate the effect of explosive type and
the effect of changing the working methodology. This will
be explained
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Table 2. Comparison of the intoxication cases due to CO in Quebec between 1991 and 2001
Rock Forest
(nov 2000)
Blast for
sewer
repair
Blast for
residential
construction
Blast for
residential
construction
Blast for
residential
construction
30 meters
8 meters
30 meters
30 meters
Yes
Yes
Yes
Yes
Yes
Blast for
Blast for
completion completion of
of a road
a road and
and services
services
22 meters
6 meters
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Blast for
installation
of pluvious
drainpipe
network
12,3 meters
Sherbrooke Rock Forest
(nov 2000) (feb 2001)
I
Rock Forest
(july 2000)
TA
Beauport
R.-du-Loup Rock Forest
(april 1995) (nov 1998) (march 2000)
,J
Location Aylmer
and date of (feb 1991)
the event
Blast on a
Type of
field
work done
neighbouring
for aqueduct
construction
53 meters
Distance
between
blasting
site and
intoxicatio
n site
Yes
Excavation
works
done more
than 1 day
after
blasting
Maximum 460* in the
concentrati drainpipe
beside the
on of CO
house
registered
(ppm)
Rock Type Limestone
500** in a
house
basement
Yes
280*** in a 195*** in the
drainpipe floor drainpipe
box and 10 and 165 in the
in the
basement
basement
Slate
Slate
Along the
cleavage
Along the
cleavage
Yes
Yes
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250-350***
1040** in a
800** in the
2000*** in a
at the first drainpipe box and drainpipe box drainpipe box
floor and
800 in the
100 in the
and 160 in the
1100 in a
basement
basement
basement
manhole
Limestone
Clayey
Slate
Slate
Slate
shale
Along the
Along the
Along the
Along the
Along the
Joints and Along the
cleavage
cleavage
cleavage
fractures lithology and lithology and cleavage
in
in
subvertical subvertical
fractures
fractures
?
Yes
Yes
Yes
Yes
Yes
Water in
borehole
Conduit
Fractured Abandonne Fractured rock
By the road Fractured rock
Probable
rock and
d conduit between houses, trench and by
between
pathway of
private
by the road trench the private
houses, by
gases
services
and by the private
services
the road
migration
entrance
services entrance
entrance
trench and
bythe private
services
entrance
5
2 (2****)
16 (3****)
4 (2****)
0 (CO detector 0 (CO detector
Number of
and 3 people and 4 people
people
evacuated)
evacuated)
intoxicated
Yes
H
OD
DI
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By the sewer Fractured rock
conduit
between
houses, by
the road
trench and the
private
services
entrance
0 (CO
0 (CO detector
detector and and 2 people
2 people
evacuated)
evacuated)
* Measures taken 3 day after the work ** Measures taken the same day that the incident by firemen ***Measures taken 2 days
after the work **** Number of people treated in hyperbaric chamber
RT
pressure measurements were installed according to
these directions and the houses were also oriented that
way. The instrumentation was aligned perpendicular to
the 4 sides of the houses. At Rock Forest, snow cover
and small trees were also removed on 80 m in the 4
directions. Because of that, the soil was frozen on 30
cm thick which created an impervious confinement.
EA
more in details in the next section. Finally, the test in
Beauport was done to see the effect of roc type and
confinement.
AN
2.2 Structural geology and instrumentation of the
experimental plots
A monitoring system installed for every house. It
consisted of: (1) 4 multilevel wells (1.3 m, 2.6 m and
3.9m depths) for gas sampling located at 1.5m, 5m,
20m, and 60m (100 m in the first test in Rock Forest) in
the four directions perpendicular to the limit of the
houses; and (2) 4 wells for pressure measurements
during blasting located at the same distance from the
house and placed 2 m beside the gas sampling wells.
A structural geology survey was performed on outcrops
and rock exposed in 3 excavations made with a
backhole at Rock Forest and in the quarry walls and
floor at Beauport in order to identify the orientation and
dip of schistosity or fractures and joints families in the
rock formations. These structures may control gas
migration in preferential pathways created by blasting
operation. Monitoring wells for gas sampling and
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–5 to +5 PSIG (GX3-P5V5G-A01-B01-C04, HighTechnology Instrument) in wells far from the blast or
the pumping wells or either pressure transducers that
range from –15 to +15 PSIG (PX205-30V15GI, Omega)
or from –15 to +60 PSIG (PX605-30V60GI) in wells
located at 1.5 and 5 m from the blast or close to the
pumping well. The pressure transducers were
connected to a data logger (CR-10 from Campbell
Scientific, Edmonton, Alta) able to record 8 data per
second.
TA
I
The multilevel wells were installed in 69 mm drilled
boreholes and were made of stainless steel tubing (3/8”
or 94 mm) connected to a stainless steel screen (100
mesh). A primary 25 cm thick sand pack (silica # 20
from Temisca Inc. and a secondary 25 cm thick sand
pack silica # 50 from Temisca Inc. was put in place
around the screened interval and every sampling point
was isolated in the borehole with bentonite grout. More
gas sampling wells were also installed in the trench at
various depth to follow CO movement. Before and after
each blast CO concentrations were monitored in many
multilevel wells installed in the rock formation around
every experimental plots. A portable gas unit (Tempest
100 from Telegan) was used in the field for carbone
monoxide analysis in interstitial gas with a limit of
detection of 1 ppm and a maximum quantification limit
of 25 000 ppm. However, the accuracy is decreased
above a CO concentration of 10 000 ppm.
Theoretical masses of explosives used and
volumes of CO produced by the blastings.
House
Total mass
Theoretical volumes
Explosives used (kg) of CO produced (m3)
Rock Forest
1
2
70.0
3
60.0
Beauport
1
EL
4.0
TRENCH
3.0
2.5
2.0
Y
1.5
30.0
1.0
-B
HOUSE 2
0.5
0.0
20.0
HOUSE 1
DI
HOUSE 3
10.0
20.0
5,39
718,62
9,67
The pumping wells for air permeability tests were
located at 7 m from the limit of the house in the 4
directions. The observation wells were located between
2 m and 11 m from the pumping wells. They were
made of 1” (25 mm) PVC tubing connected to a 1.50 m
long PVC screen (slot 0.020”) located at 2.60 m depth.
A filter sand pack (silica #20 from Temisca Inc.) was
put in the annular space between the borehole wall and
the PVC screen up 2.6 m and completed with 10 cm of
secondary sand filter (silica #50) and sealed up to the
surface with bentonite grout. The pumping test was
done with a pump that can generate up to 0.8 atm of
vacuum (SIHI, LPHB 3408, 5HP). More pumping wells
were also installed in the trench and in the HOUSES 1
and 2 after the blasts in order to be able to pump the
remaining carbon monoxide still present in the
fractured rock before the next test. The data of
pressure versus time collected from air permeability
test were analysed with HYPERVENTILATE software
conceived by Jonshon and Stabenau from the Shell
Development Westhollow Research Center.
30.0 (m)
Localisation of experimental plots at Rock
Forest and overburden thicknesses.
RT
Figure 1.
0.0
225,54
H
-20.0 -10.0
OD
0.0
-10.0
TY
(m)
10.0
2,94
3,85
RA
3.5
40.0
199,41
251,38
CH
4.5
50.0
,J
(m)
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Table 3.
AN
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The wells for pressure measurements were made of
stainless steel tubing with a screen interval located at 3
m depth. At Beauport they were made of 6.35 mm
HDPE tubing located between 2.80 m and 3.00 m
depths. There was sand in each well from the bottom to
2 m deep. The wells installed for interstitial air pressure
survey have two objectives: (1) evaluation of the air
permeability of the rock formations during a pumping
test and; (2) measurements of gas pressure generated
by blasting in order to evaluate the transport
mechanism of gases involved. The pressure was
surveyed in the monitoring system during blasting or air
pumping test by pressure transducers that range from
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Figure 2. Explosives used and borehole charging for
the Rock Forest and Beauport tests.
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o
o
fractures is oriented at N115 and N205 . Also the sub
horizontal stratification is well developed.
The air permeability test performed at Beauport
indicates a good air permeability of the rock formation
at about 90 darcy (Figure 4). This test means that the
fractures of the Trenton group are connected in the
tested area. The test was done on the west side of the
house only because all other pumping wells were partly
saturated with water. At Rock Forest the air
permeability test showed that the rock formation was
tight and impervious because the detection limit of the
pressure transducer in the observation wells was not
reached for the vacuum applied at the pumping wells.
This observation can be corroborated to the fact that a
very low flow rate was monitored at the exhaust of the
pump and a suction can be felt in the pumping well
when the pump tubing was disconnected from the
pumping well. An air permeability test was also done in
the trench created at Rock Forest and this time the
fractured rock was so permeable that again the
detection limit of the pressure transducer in the
observation wells could be reached with the vacuum
applied in the pumping well. This was confirmed by the
pressure transducer on the pumping system, that
indicated a very low vacuum and a very high flow rate
(1302.6 l/min).
2.3 Blasting operation
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For all the tests the blasting operation was the same as
usually done by specialist firms for house construction.
Two to three blasts were done for each house in the
same day. The 2.75” (69 mm) boreholes were drilled
down to 14 feet (4.2 m) and charged with the same
quantity of explosives. The explosives were supplied
graciously by Dyno Nobel Inc. Granular ANFO (Numex)
in dry boreholes or emulsified ANFO (Dynotec 62.5 mm
x 400 mm) in wet boreholes where used for the tests
(see Figure 2). The ANFO was placed above the prime
charge (Unimax TST 62.5 mm x 400 mm) that is
connected to a detonator (Handidet). This subsurface
detonator was connected to a surface detonator (HTD)
to initiate the blast of charged boreholes with the
appropriate delays. The rest of the borehole was filled
with gravel and cuttings to the top. The spacing
between boreholes was kept between 1.35 to 1.50 m.
An average of 225 kg of explosives were used for each
test (Table 3). The theoretical volume of CO produced
by each test is 5140 l.
0
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241
361
Time (sec)
481
601
Figure 4. Air permeability test in observation well
located at 1.5 m from the limit of the house
at Beauport.
3.2 Carbon Monoxide measurements
Joint - 2 (035° / 80°)
H
3.2.1 Rock Forest HOUSE 1
RT
Figure 3. Stereographic projection (equal area) of
geological structures at Rock Forest.
EA
Figure 5 shows carbon monoxide concentrations
observed in the monitoring system immediately after
the three blasts (A, B and C) of HOUSE 1 (t =0) and
after 1 to 6 days. The isoconcentration lines were
drawn with Surfer v.6 and the interpolation was made
by triangulation. At t=0 the gas generated by the
explosions had traveled up to 7 m from the side of the
house created and the concentration in carbon
monoxide reached more than 20 000 ppm. The
transport mechanism responsible of gas migration in
the fractures created is advection. After one day the
spreading of CO is increased by diffusion in the
fractures created. Three days after the blasts the
maximum extent of the high concentration zone(> 10
000 ppm) is reached and the diffusion mechanism
3.1 Structural geology and air permeability test
AN
At Rock Forest the preferential orientation of geological
structure are related to the methamorphism of the rock.
o
The schistosity in the rock is oriented at N60 with a dip
o
of 65 (Figure 3). The schistosity is not penetrative. A
major family of joints (joint 1) is oriented perpendicular
o
o
to the schistosity at N150 with a dip of 75 . A second
family of joints (joint 2) is also present but not well
developed. At Beauport a family of sub vertical
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-1,5
1
Schistosity (060°/ 65°)
Joint - 1 (150° / 75°)
3 RESULTS
-1
-3,5
OD
Legend
Pressure (in. water)
-B
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RA
-0,5
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and its eventual transport by diffusion could be easily
mitigated by pumping interstitial air immediately after
the blasts with a vacuum pump connected to a
properly installed pumping well.
created a preferential movement of the gas at 15 m
o
from the house in the family of joints at 150 that were
opened by the blasts. The contamination extent further
after 6 days but the CO concentrations had decreased
a lot.
3.2.3 Rock Forest HOUSE 2
3.2.2 Rock Forest TRENCH
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The first blast (G) of HOUSE 2 allowed to create a
trench for the private services and to blast the first half
of the house (Figure 7). The pressure generated by the
blast was monitored in the observation wells located
around the house. The data collected showed two
different behaviours of pressure in the trench and in the
tight rock formation (Figure 8). In the trench (T 13.5
located at 3 m from the private services trench), the
gas pressure is positive and sharp indicating that the
gas is pushed quickly into the open muck of the trench.
The advection front of the gas makes a pulse that last
less than 0.5 sec. In the rock formation adjacent to the
blasted HOUSE 2 (2OP-19 located at 1.5 m from the
limit of the house) the pressure generated is negative.
In fact, the blast had generated fractures (voids) in the
rock and these voids that are under negative pressure
create a suction on the gas from the blasted area that
moves to equilibrate the pressure. The fractures in the
rock are generated in less than 0.5 sec after the blast
and the suction applied by the voids created lasted 4
to 5 sec. So, the movement of gas immediately after a
blast is by advection. The gas is pushed in the muck
(rock already fractured) or is sucked by the fractures
generated in the adjacent tight rocks.
-B
Y
The test in the second house was made after the
construction of a trench of 60 m long, 4 m deep and 3
m wide to simulate a road with public services. This
trench was instrumented extensively with gas sampling
and pressure measurement wells. A water pumping
well was installedat the junction between the trench
and HOUSE 1 in order to keep the water table as low
as possible (4m depth). The pumping well kept the gas
monitoring wells in the trench free of water. The flow
rate was maintained at 20 l/min during the following
tests. The rock of the trench close to HOUSE 1 was
not completely fractured and the blasting was done
again. This blast generated high concentrations of CO
in this part of the trench and in the HOUSE 1 as well.
Air pumping wells were put in place in HOUSE 1 (two)
and in the trench (four) in order to lower the CO
concentration to zero before performing the test in
House 2. The pumping wells were pumped for a few
hours until the concentration in the exhaust air was
undetectable. As an example, Figure 6a shows the
recovery curve of carbon monoxide in HOUSE 1 as a
function of air volume extracted. This operation took
15.6 hours at a pumping rate of 1302.6 l/min and was
very efficient to lower the concentration of CO in gas
sampling wells to low levels (Figure 6b). This
experiment shows that CO concentration generated by
blasts in the fractured rock
op1.5
se5
se1.5
sp5
sp1.5
10000
oe1.5
A
B
C
ne1.5
ne5
np1.5
np5
se5
se1.5
sp5
sp1.5
A
B
ne1.5
ne5
DI
op1.5
oe1.5
TY
oe5
oe5
C
np1.5
OD
ep1.5
ep1.5
1000
np5
100
ee5
ee5
B)
B) tT== 11 day
DAY
H
A) After the explosions t = 0
se1.5
sp5
sp1.5
A
B
C
1
oe5
0
(ppm)
op1.5 oe1.5
ne1 .5
ne5
np1 .5
np5
ep1 .5
AN
ee5
C) t = 3 days
se5
EA
se5
oe1 .5
RT
oe5
op1 .5
10
sp5
se1.5
sp1.5
A
B
C
ne1.5 ne5
np1.5 np5
ep1.5
ee5
0
10 m
D) t = 6 days
Figure 5. Carbon monoxide concentrations observed in
the monitoring network after House 1 blasts
at Rock Forest.
The International Association of Hydrogeologists
l'Association Internationale des Hydrogéologues
1461
Immediately after the second blast (H) of HOUSE 2 the
carbon monoxide concentrations, as observed in the
monitoring system, were spread by advection up to 8 m
from the limit of HOUSE 2 in the fractured rock created
by the blasts. The maximum concentration of CO
recorded was higher than 20 000 ppm. As for HOUSE
1 the preferential movement of the carbon monoxide
o
was more extensive along the family of joints at 150 .
The gas travelled more easily by advection in the
previously fractured rock (muck) of the trench and it
reached a distance of 20 m from HOUSE 2. Also the
neighboured HOUSE 1 was contaminated. The CO
entered in HOUSE 1 via the trench but also via the
fractured rock created between the 2 houses by the
blasts made in each house. This situation can explain
some of the CO intoxication that occurred in houses of
Rock Forest. This was confirmed at one day after the
blast of HOUSE 2. After 3 days the spreading of CO is
not increased by diffusion in the fractures created in the
rock formation because the travelled distance by CO
stays the same. However, the maximum extent of the
contamination is observed after 3 days where the
diffusion is responsible for the transport of CO to 28 m
from the limit of HOUSE 2 in the trench. After 3 days
the CO concentration decreased drastically in the
trench because of higher dilution and ventilation by
exposed blasted rock at the far end of the trench. CO
concentration persisted after 6 days in HOUSE 2 and in
the surrounding fractured rock but the concentration
had decreased by one order of magnitude.
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La Société canadienne de Géotechnique
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2001 Odyssée de la Terre
the next blast; (2) the sequence of blasting ends the
public services trench instead of beginning with this
blast; (3) the installation of 5 vents (open boreholes
without charge) in the rock at the last blast at the end of
the private services trench in order to limit the migration
of CO in the main trench (simulated road). In the last
blast of the test the velocity of detonation (VOD) was
measured in explosives of two boreholes. In one of the
borehole the measured VOD was 5200 m/s. The same
VOD was recorded in the bottom UNIMAX TST and the
3 BLASTEX PLUS cartridge placed above indicating a
very good blast. In the second borehole VOD was 4355
m/s in the UNIMAX TST and only 1398 m/s in the two
BLASTEX PLUS cartridges placed above indicating a
deflagration instead of a detonation. These results
show that the blast was good but not perfect as often
observed under field conditions. Also, the swelling was
good and a grey fumes escape from the blast indicating
the success of that blast.
Mass of CO extracted from the pumping well MC-1 in Rock
Forest. 02/21/01
Mass: 11,70 grams
TA
I
90
80
70
60
50
40
30
20
10
0
20
40
60
80
100
Cumulative volume (m3)
120
140
&
0
IE
A)
AM
t-41. 5
t-40
10000
t-37. 5
t-32. 5
1000
oe30 2op30
t-30
,J
Concentration (ppm)
2001 An Earth Odyssey
t-28. 5
t-28
t-41.5
100
10
2oe19 2op19
t-19
oe30 2op30
t-30
G H
t-12
2ne5
2ne10
2np5
2np10
1
t-22.5
2oe8.52op8.5
0
t-6.5
2oe5 2op5
t-5
(ppm)
op1. 5
oe1. 52op1.5
M O-1
M S-1
sp5
M C-1
ne1. 5
ne5
np1. 5
np5
M N-1
sp1.5
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10 m
ep1. 5
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B)
t -22. 5
2oe19 2op19
t-15
2oe19 2op19
t -19
G
t-12
H
2ne5
2ne10
2np5
2np10
10
t -15
G H
t -12
2oe8.5 2op8.5
2oe5 2op5
t-5
op1.5
sp1.5
op1. 5
ne1.5
s e5
s e1.5
s p5
s p1.5
M C- 1
M N-1
np1.5
TY
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DI
B) t = 1 day
t-41. 5
t -41.5
t-40
t -40
OD
t -37.5
t-32. 5
t -32.5
oe30 2op30
t-30
oe30 2op30
t -30
t-28. 5
t-28
H
np5
ep1. 5
t-37. 5
t -28.5
t -28
t-23
2oe22.5
2op22.5
t -22.5
2oe22.5
2op22.5
t -23
2oe19 2op19
t-19
RT
ne5
np1. 5
M N- 1
np5
A) After the explosions t = 0
2oe19 2op19
t -19
t-17. 5
t -17.5
t-15
G H
t-12
EA
ne1. 5
M S- 1
M C-1
2ne5
2ne10
2np5
2np10
G H
t -15
t -12
2oe8.52op8.5
t-8
oe1. 5 2op1.5
op1.5
oe1.5 2op1. 5
M O- 1
0
M O-1
s e1.5
AN
ne5
s e5
s e1.5
M S-1
M C-1
s p5
ne1.5
ne5
np1.5
np5
M S- 1
M N-1
M C- 1
s p1.5
np1. 5
np5
s p5
M N- 1
s p1.5
ep1. 5
ep1.5
For the test in HOUSE 3 special procedures were
applied in order to limit the CO production and
migration in the fractured rock during blasting. These
procedures were: (1) excavation (ventilation) of the
debris (muck and the overburden) after each blast and
filling up of the excavation with all this material before
ee5
ee5
C) t = 3 days
1462
2np10
2oe5 2op5
t -5
op1. 5
3.2.4 Rock Forest HOUSE 3
2ne10
2np5
t -6.5
2oe5 2op5
t-5
s e5
2ne5
2oe8. 52op8. 5
t -8
t-6. 5
ne1. 5
The International Association of Hydrogeologists
l'Association Internationale des Hydrogéologues
(ppm)
ne5
M S -1
t-22. 5
0
oe1. 5 2op1. 5
ee5
created by the blasts. A 3-D map was produced with
Surfer and the volume of broken rock and overburden
above natural ground level was calculated. The ratio of
this volume to the volume of the initial blasted material
gave a swelling of 35.2% for the overall blasts. The
swelling is an indication of the success of all the blasts.
The porosity of the muck is estimated at 25%.
1
M O- 1
ep1.5
After this test a topographic survey was made on all the
blasted area (HOUSE 1, HOUSE 2 and the trench) and
surrounding land to estimate the swelling of the rock
Figure 6. Interstitial air purging after blasting of trench.
a) Mass of CO extracted from a pumping well installed
in house 1 at Rock Forest.
b) CO concentrations in the monitoring system after air
purging.
2np10
2oe5 2op5
t -5
oe1.5 2op1.5
M O-1
se1.5
2ne10
2np5
t -6.5
t-6.5
sp5
2ne5
2oe8. 52op8. 5
t -8
t-8
se5
100
2oe22.5
2op22.5
t -23
t -17. 5
t-17.5
Y
se1.5
-B
se5
2oe22.52op22.5
t-23
t-19
RA
t-8
1000
oe30 2op30
t -30
t -28. 5
t -28
t-28.5
t-28
CH
t-15
t -32. 5
t-32.5
t-17. 5
10000
t -37. 5
t-37.5
2oe22.5
2op22.5
t-23
t-22. 5
t -41. 5
t -40
EL
t-40
D) t = 6 days
The Canadian Geotechnical Society
La Société canadienne de Géotechnique
10 m
BACK TO TABLE OF CONTENTS
2001 An Earth Odyssey
2001 Odyssée de la Terre
from the limit of the house was in the direction of the
o
family of joints surveyed at 150 . In the trench, the
travelled distance of CO by advection was 12 m. Also
initially HOUSE 1 and 2 were not invaded by CO. The
low concentration of CO observed originated from the
test of HOUSE 2 performed the week before. However,
one day after the blasts HOUSE 1 and 2 were
contaminated by the CO transported by diffusion in the
trench. The maximum extent of 10 m was observed
after 2 to 3 days in the fractured rock created by the
blasts(Figure 10). So only 2 m of migration of CO was
added by diffusion in the fractured rock. In the trench, a
6 m of migration by diffusion was added going from 10
m to 16 m of travelling distance in 6 days. The dilution
by a larger volume of interstitial air created by the
trench and the two houses blasted could be
responsible of the shorter migration distance of CO in
the ground. The complete excavation of the muck was
done at day 6 to evaluate its effect on CO
concentrations. The very low level of CO observed in
the monitoring system after one day showed that this
technique has a good potential as remedial action. A
specific test is undergoing to prove the reliability of this
technique.
Figure 7. Carbon monoxide concentrations observed in
the monitoring network after House 2 blasts
at Rock Forest.
House 2 - Rock Forest, blast G
2
I
T-13.5
TA
0
&
-1
IE
-2
20P-19
-3
AM
Pressure (in, water)
1
-4
-10
0
10
Time (sec)
20
oe30 2op30
t-30
oe30 2op30
t-28.5
t-28
10000
3sp1.5
MN-2
MS-2
t-13.5 t-14
2ne5
3op5
3op1.5
2oe5
MN-2
MS-2
2np5
ME-2
t-9.5
3sp5
3sp1.5
K
I
2oe5
t-5
2op5
3ee1.5 3ep1.5
op1.5
3ep5
op1.5
oe1.5 2op1.5
3ee5
MO-1
3ep5
MS-1
3ee10 3ep10
MN-1
MN-1
np1.5
np5
np1.5
ep1.5
ee5
oe3 0
B) t = 1 day
OD
A) After the explosions t = 0
2op 30
t- 30
3op 5
3oe 1.5
3op 1.5
t- 22.5
3oe 10
2oe 22.52op 22.5
2oe 19 2op 19
MO MO
S- 2N- 2
t- 19
t- 17.5
t- 12.5
J
3sp5
3sp1 .5
I
2oe 8.5 2op 8.5
3sp5
t- 8
t- 6.5
2oe 5
t- 5
2op 5
3sp1 .5
oe1 .5 2op 1.5
MO -1
EA
op1 .5
3ep 5
3oe 1.5
3op 1.5
EL
(ppm)
I
-15
2oe 22.52op 22.5
t- 23
-20
2oe 19 2op 19
MO MO
S- 2N- 2
t- 19
MN- 2
MS-2
t- 15
t- 14
t- 13.5
-25
2ne 5
2np 5
t- 12.5
ME-2
t- 9.5
-30
2oe 8.5 2op 8.5
t- 8
3ee 5
MS -1
MN- 1
np1 .5
ep1 .5
t- 6.5
2oe 5
t- 5
2op 5
op1 .5
3ep 5
-35
oe1 .5 2op 1.5
0
MO -1
10 m
-10
MS-1
MN- 1
np1 .5
np5
ep1 .5
ee5
AN
10
20
Figure 10. Pressures recorded as a function of time
during blast B in two monitoring wells at
Beauport.
np5
6 days
D)D)
T =t =
6 DAYS
Figure 9. Carbon monoxide concentrations observed in
the monitoring network after House 3 blasts
at Rock Forest.
The International Association of Hydrogeologists
l'Association Internationale des Hydrogéologues
0
Time (sec)
ne1 .5
3ee 10 3ep 10
ee5
C) t = 3 days
0
-5
-10
oe3 0 2op 30
t- 17.5
K
ne1 .5
3ee 10 3ep 10
5
0
3ee 1.5 3ep 1.5
3ee 1.5 3ep 1.5
3ee 5
3op 5
J
ME -2
t- 9.5
K
2ne 5
2np 5
t- 22.5
3oe 5
RT
MN- 2
MS -2
t- 15
t- 13.5 t- 14
3op 10
H
3oe 5
10
t- 28.5
t- 28
t- 28.5
t- 28
t- 23
House 1 - Beauport, blast B
1
np5
DI
ep1.5
ee5
t- 30
CH
ne1.5
MS-1
3ee10 3ep10
10
oe1.5 2op1.5
MO-1
ne1.5
3op 10
100
2oe8.5 2op8.5
t-8
t-6.5
2op5
3ee1.5 3ep1.5
3oe 10
1000
2ne5
t-12.5
ME-2
2oe8.5 2op8.5
t-8
t-6.5
t-5
3ee5
t-15
t-13.5t-14
J
t-9.5
K
I
2oe19 2op19
MOS-2
MON-2
t-17.5
2np5
t-12.5
J
3sp5
3oe5
3oe1.5
t-17.5
t-15
2oe22.52op22.5
t-23
TY
3op5
3op1.5
t-22.5
t-19
2oe19 2op19
MON-2
MOS-2
t-19
3oe5
3oe1.5
3op10
2oe22.52op22.5
t-23
t-22.5
Y
3op10
-B
3oe10
3oe10
At Beauport the site of experimentation was located in
fractured limestone rock covered with less than one
meter of sand. Three blasts were made in the same
day. The monitoring of pressure in the monitoring
system showed that the generated gas by the blast was
first injected rapidly in the fractures already present in
the rock as shown by the positive pressure peak at 1.5
m from the limit of the house in Figure 10. The
generation of new fractures in the rock formation by the
blast created voids under negative pressure that pull on
Pressure (in. water)
t-30
t-28.5
t-28
3.2.5 Beauport
RA
In HOUSE 3 after the three blasts the same maximum
concentration of CO (> 20 000 ppm) was observed in
the monitoring system. The migration of CO by
advection in the fractured rock immediately after the
blast was anisotropic. The maximum extent of 6 to 8 m
,J
Figure 8. Pressure recorded as a function of time
during the blast of House 2 in two monitoring
wells at Rock Forest.
4.
CONCLUSION
the gas of the blast at 1.5 and 5 m from the limit of the
house. The suction was not as important at 20 m from
the limit of the blasted house. The CO concentration
1463
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La Société canadienne de Géotechnique
BACK TO TABLE OF CONTENTS
2001 An Earth Odyssey
2001 Odyssée de la Terre
concentrations infiltrating their house. Along a road with
underground public services the distance for security
control with CO detector in houses may be increased to
75 m from the blast. Two mitigation technique may also
be applied to minimise CO migration after a blast:
pumping of gas within the muck produced by blasting
rock may significantly and efficiently remove CO if
appropriate pumping wells and vacuum pumps are
used. The test perform in HOUSE 1 at Rock Forest
demonstrated that. The complete excavation of the
muck after blasts can also have a significant effect on
CO migration and removal in the surrounding fractured
rock but more test are needed to prove this point.
We thank Dre Uta Gabriel and M. Thomas Robert for
their help in field work. This project was funded through
a grant from l’Institut de recherche en santé et sécurité
au travail (IRSST), and a research contract from the
ministère de la santé et des services sociaux (MSSS),
ministère des transports (MTQ) and the ministère de
l’environnement
of
Québec
(MENVQ).
We
acknowledge Dyno Nobel for providing explosives. We
also thank the technical support of M. Pierre Dorval
(MTQ), Jean Pelletier (MENVQ) and Marc Baril
(IRSST).
RA
CH
EL
,J
The structural geology of rock formation (schistosity,
family of joints, fractures) plays a role in the direction
and length of propagation of gas in fractures generated
when rock is blasted with explosives. The type of
confinement of the rock can affect the quantity of gas
migrating in the fractured rock.
6.
-B
Y
For the Rock Forest and Beauport tests some
conclusions may be drawn. Significant concentrations
of CO may persist in the fractured rock even 7 days
after a blast. Advection is the initial mechanism of CO
migration in fractured rock generated by the blasts or
naturally occurring before the blast. The distance of
migration with this mechanism is short (5 to 8 m). In
trenches of mucks (equivalent to fills under roads) the
distance of CO migration by advection is 12 to 20 m. In
the 2 to 3 days following the blasts, further CO
migration up to 15 m is made by diffusion in the
induced fractures or up to 30 m in the trenches.
However, no further migration by diffusion seemed to
happen in the naturally occurring fractures in the rock
of Beauport. The CO concentrations decreased after
two to three days in the underground and this was
caused by dilution with interstitial air.
REFERENCES
Auger P.L., Lévesque B., Martel R., Prud’homme H.,
Bellemare D., Barbeau C., Lachance P., Rhainds M.
An unusual case of carbon monoxide poisoning. Env
Health Perspect 1999; 107:603-605
DI
TY
NIOSH. Hazard ID, CO poisoning and death after the
use of explosives in sewer construction projects, Niosh,
DHHS Publication, 1998, p. 98-122.
OD
Dougherty, F, FT. Loyle, J. Kunz, LK. Felleisen. An
environmental case study involving carbon monoxide
infiltration of nearby residencies during sewer
trenching, Proceedings of Indoor Air 90, Toronto,
Canada, vol. 3, 1990, p. 753-758.
H
From the review of intoxication cases the distance of
migration of CO may reach 55 m if a conduit is present
underground. Broken underground conduit by blasts, fill
around underground conduits in road trench or house
trench or fractured rock created by blasts between
houses or between a house and a road are the
different pathways identified in the Québec incidents.
RT
Meredith T., and A. Vale, Carbon monoxide poisoning.
Br Med J 1998; 296:77-78.
Recommandations sur la problématique d’intoxication
au monoxyde de carbone associés aux travaux à
l’explosif en milieu habité, MSSS et MENVQ, 2001.
EA
The special procedures applied to limit the CO
production and migration in the fractured rock during
blasting did not have a significant effect. These
procedures were: (1) the excavation and refilling
(ventilation) of the muck and the overburden after each
blast, (2) the installation of vents in the rock around the
blast, (3) the modification of the blasting sequence and
(4) the modification of explosive type.
AN
Regional municipality of Hamilton-Westworth Teaching
Health Unit, Carbon monoxide incident in HamiltonWestworth: Public health and epidemiology report,
Ontario, vol. 6, 1995, p. 239-241.
SANTIS, L.D., A Summary of Subsurface Carbone
Monoxide Migration Incidents, International society of
explosives, 2001.
A CO detector with an alarm must be put inside every
house located within a radial distance of 30 m from a
blast in order to warn people of significant CO
The International Association of Hydrogeologists
l'Association Internationale des Hydrogéologues
ACKNOWLEDGMENTS
AM
5.
IE
&
TA
I
measured in the monitoring system was less important
than in the tests at Rock Forest. During the Beauport
test a large proportion of the generated gas by the
blasts was escaping in the atmosphere caused by the
low confinement of the limestone by sand. However, an
orange fume was escaping that indicates a deflagration
of explosives in many boreholes. This situation should
have generated more CO than for a blast. The
migration of CO by advection in the ground was
observed to 5 m from the limit of the house and no
further movement of the gas by diffusion seemed to
have occurred (the next observation well being installed
at 20 m). The weak confinement of the blast was
probably responsible of these results. The blasts of the
Beauport accident in 1995 was made under asphalt
road that help to confine the gas produced and the
carbon monoxide had migrated up to 12 m.
1464
The Canadian Geotechnical Society
La Société canadienne de Géotechnique
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