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Carbon monoxide poisoning associated with blasting operations close to underground enclosed spaces. Part 1. CO production and migration mechanisms.
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Carbon monoxide poisoning associated with blasting operations close to underground enclosed spaces. Part 1. CO production and migration mechanisms Richard Martel, Luc Trépanier, Benoît Lévesque, Guy Sanfaçon, Patrick Brousseau, Marc-André Lavigne, Louis-Charles Boutin, Pierre Auger, Denis Gauvin, and Louise Galarneau

Abstract: Explosives used for blasting operations in civil engineering works can generate large volumes of carbon monoxide (CO). The production of 10–24 L of CO per kilogram of explosives blasted is theoretically possible. CO can migrate a considerable distance in the fractured rock of the blasted areas and then infiltrate closed spaces (sewage systems, manholes, basements of houses). In the Province of Quebec, in the last 10 years, seven people were poisoned by CO in their houses to the extent that they had to be treated in a hyperbaric chamber. Underground conduits broken by blasting, filling around underground conduits in road or house trenches, or fractured rock created by blasts between houses or between a house and a road are the different CO pathways identified in the Quebec incidents. Field tests done by our group show that (i) the structural geology of the rock formation (schistosity, family of joints and fractures) controls the direction and extent of gas migration in fractures generated by blasts; (ii) the confinement of the rock can affect the quantity of gas migrating in the fractured rock; (iii) significant concentrations of CO may persist in the fractured rock 7 days after a blast; (iv) advection is the initial mechanism of CO migration immediately after a blast, and the distance of migration varied from 8 m in the fractured rock to 20 m in the fills of a road trench; and (v) further CO migration by diffusion up to 15 m in the induced fractures and 30 m in fills may occur in the 3 days following a blast. Key words: carbon monoxide, blasting, poisoning, enclosed spaces, gas migration, house. Résumé : Les explosifs utilisés pour les opérations de sautage lors de travaux en génie civil382 peuvent générés de grands volume de monoxyde de carbone (CO). La production de 10 à 24 L de CO par kg d’explosifs est théoriquement possible. Le CO peut migrer sur des distances considérables dans les fractures du roc de la zone dynamitée et peut infiltrer des espaces clos (tuyaux d’égouts, trou d’homme et sous-sols de maisons). Au Québec, au cours des 10 dernières années, sept personnes ont été intoxiquées par le CO dans leurs résidences à un point tel qu’ils ont du être traitées dans une chambre hyperbare. Les différents chemins empruntés par les gaz dans les incidents québécois sont : conduits souterrains brisés par le sautage, le remblai des tranchées de routes ou des entrées de services des maisons, le roc fracturé créé entre les maisons ou entre les maisons et la route par les sautages. Des essais de terrains effectués par notre groupe démontrent que : (i) la géologie structurale de la formation de roc (schistosité, famille de joints, fractures) contrôle la direction et l’étendue de la migration du CO; (ii) le confinement du roc peut affecter la quantité de gaz migrant dans le roc fracture; (iii) des concentrations significatives de CO peuvent persister dans le roc fracturé 7 jours après les sautages; (iv) le mécanisme responsable de la migration du CO immédiatement après un sautage est l’advection et la distance de migration du CO a varié de 8 m dans le roc fracturé jusqu’à 20 m dans la tranchée de la route; et (v) une migration du CO par diffusion allant de 15 m dans le roc fracturé jusqu’à 30 m dans la tranchée de la route s’est produite pendant les 3 jours suivant les travaux aux explosifs. Mots clés : monoxyde de carbone, sautage, intoxication, espace clos, migration de gaz, résidence. Martel et al. Received 28 June 2002. Accepted 19 December 2003. Published on the NRC Research Press Web site at http://cgj.nrc.ca on 16 June 2004. R. Martel,1 L. Trépanier, M.-A. Lavigne, and L.-C. Boutin. INRS-Eau, Terre et Environnement, Centre géoscientifique de Québec, 880, chemin Sainte-Foy, bureau 840, Québec City, QC G1S 2L2, Canada. B. Lévesque, G. Sanfaçon, P. Auger, D. Gauvin, and L. Galarneau. Direction risques biologiques, environnementaux et occupationnels, Unité santé et environnement, Institut National de Santé Publique du Québec, Sainte-Foy, QC G1V 5B3, Canada. P. Brousseau. Defence R&D Canada, Valcartier (DRDC), 2459 Pie-XI Blvd. North, Val-Bélair, QC G3J 1X5, Canada. 1

Corresponding author (e-mail: [email protected]).

Can. Geotech. J. 41: 371–382 (2004)

doi: 10.1139/T04-001

© 2004 NRC Canada

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Table 1. Comparison of the intoxication cases due to CO in Quebec between 1991 and 2001. Rivière-du-Loup, Nov. 1998

Rock Forest, Mar. 2000

Blasting for sewer repair

Blasting for residential construction

30

8

Yes

Yes

Yes

460a in the drainpipe beside the house

500b in a house basement

1040b in a drainpipe box; 800 in the basement

Limestone Along the lithology and in subvertical fractures ? Conduit

Limestone Along the lithology and in subvertical fractures Yes Fractured rock and private services entrance

250–350c at the first floor; 1100 in a manhole Clayey shale Along the cleavage

5

2 (2d)

Location and date

Aylmer, Feb. 1991

Beauport, Apr. 1995

Type of work done

Blasting of a neighbouring field for aqueduct construction 53

Blasting for installation of a rainwater drainpipe network 12.3

Yes

Distance between blasting site and intoxication site (m) Excavation works done more than 1 day after blasting Maximum concentration of CO registered (ppm) Rock type Joints and fractures

Water in borehole Probable pathway of gas migration

No. of people intoxicated

Yes Abandoned conduit

16 (3d)

Slate Along the cleavage

Yes Fractured rock between houses, by the road trench, and by the private services entrance 4 (2d)

a

Measurement taken 3 days after the work. Measurements taken by firemen the same day as the incident. c Measurements taken 2 days after the work. d Number of people treated in a hyperbaric chamber. b

Introduction Carbon monoxide (CO) is a gas with no characteristic colour, smell, or taste and is not irritating, and therefore cannot be detected by human senses. When it is absorbed by the respiratory system, CO is rapidly transferred to the circulatory system. In the blood, it develops an affinity with haemoglobin that is 200–250 times higher than that of oxygen (Meredith and Vale 1998). There have been many cases of CO intoxication attributed to the presence of an engine or a combustion heating system. The reference-limit value for CO in houses is very low (10 000 ppm) was reached and the diffusion mechanism created a preferential movement of the gas at 15 m from the house in the family of joints at 150° that were opened by the blasts. The contamination extended farther after 6 days, but the CO concentrations had decreased very significantly.

draw the curves from 0 to over 10 000 ppm on a logarithmic scale.

Results Structural geology and air permeability test At Rock Forest the preferential orientation of the geological structure is related to the metamorphism of the rock. The schistosity in the rock is oriented at N60° with a dip of 65°. The schistosity is not penetrative. A major family of joints is oriented perpendicular to the schistosity at N150° with a dip of 75°. A second family of joints is also present but not well developed. 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 with the fact that a very low flow rate was monitored at the exhaust of the pump and 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 not be reached with the vacuum applied in the pumping well. This was confirmed by the pressure transducer on the pumping system, which indicated a very low vacuum and a very high flow rate (1302.6 L/

Rock Forest house 2 The first blast (blast G) at house 2 allowed creation of a trench for the private services and the first half of the house (Fig. 6). The pressure generated by the blast was monitored in the observation wells located around the house. The data collected showed two different behaviours of the pressure in the trench and in the tight rock formation (Fig. 7). In the trench (T-13.5 located at 3 m from the private services trench), the gas pressure was positive and sharp, indicating that the gas was pushed quickly into the broken rock of the trench. The advection front of the gas created a pulse that lasted less than 0.5 s. In the tight rock formation adjacent to the blasted house 2 (2OP-19 located 1.5 m from the limit of the house), the pressure generated was negative. In fact, the blast generated fractures (voids) in the initially tight rock formation, and these fractures, under negative pressure, created suction on the gases produced in the blasted area. The produced gases then moved into the generated fractures to equilibrate the pressure. The fractures were generated in the rock formation in less than 0.5 s after the blast, and the suction applied by these created voids lasted 4 to 5 s. Therefore, the movement of gas immediately after a blast is by advection. The gas is pushed into the broken rock (or rock naturally fractured) or is sucked by the fractures generated in the adjacent tight rock. Immediately after the second blast (blast H) of house 2, the CO 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 iso© 2004 NRC Canada

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Can. Geotech. J. Vol. 41, 2004 Table 4. Quantities of explosives used and theoretical masses and volumes of CO produced by the blasting operations.

House

Weight of Numex (kg)

Weight of Unimax (kg)

Rock Forest 1 Rock Forest 2 Beauport

141.00 160.00 355.70

39.36 66.42 54.72

Weight of Dynotex (kg) 19.05 24.96 101.40

Fig. 4. Air permeability test in observation well located 1.5 m from the limit of the house at Beauport.

Total weight of explosives used (kg)

Theoretical mass of CO produced (kg)

Theoretical volume of CO produced (m3)

199.41 251.38 511.82

3.37 4.41 7.95

2.94 3.85 6.94

Fig. 6. Carbon monoxide concentrations observed in the monitoring network after the two blasts (G and H) at house 2 at Rock Forest: (a) immediately after the explosions (t = 0 days), (b) at t = 1 day, (c) at t = 3 days, and (d) at t = 6 days.

Fig. 5. Carbon monoxide concentrations observed in the monitoring network after the three blasts (A, B, and C) at house 1 at Rock Forest: (a) immediately after the explosions (t = 0 days), (b) at t = 1 day, (c) at t = 3 days, and (d) at t = 6 days.

concentration lines were drawn with Surfer version 6, and the interpolation was made by triangulation. The maximum concentration of CO recorded was higher than 20 000 ppm. As for house 1, the preferential movement of CO was more extensive along the family of joints at 150°. The gas travelled more easily by advection in the previously broken rock (muck) of the trench and reached a distance of 20 m from

house 2. Also, the neighbouring house 1 was contaminated. The CO entered house 1 via the trench but also via the fractured rock created between the two houses by the blast made in each house. This situation can explain some of the high CO concentrations that occurred in the houses of Rock For© 2004 NRC Canada

Martel et al.

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Fig. 7. Gas pressure (1 psi = 6.895 kPa) as a function of time in the observation wells located in the trench (T-13.5) and in the bedrock after blast G at house 2 at Rock Forest. Overburden thickness in metres.

Fig. 8. Cross section A–A′ of the carbon monoxide concentrations observed in the monitoring system of the main trench immediately after the blasting operations at house 2 at Rock Forest (see Fig. 6 for location of cross section).

est. This was confirmed 1 day after the blast at house 2. After 3 days the spreading of CO was not increased by diffusion in the fractures created in the tight rock formation because the distance travelled by CO remained the same. The maximum extent of the contamination was observed at t = 3 days, however, when diffusion was responsible for the transport of CO to 28 m from the limit of house 2 in the main trench. After 3 days the CO concentration decreased drastically in the trench because of higher dilution and ventilation from exposed blasted rock at the far end of the trench. CO concentration still persisted after 6 days in house 2 and

in the surrounding fractured rock, but the concentration had decreased by one order of magnitude. The CO concentrations measured along the main trench (Fig. 8) immediately after the blasts show that the gas was emitted via the broken rock of the private services trench of house 2 and via the fractured rock between the house and the main trench. At this location concentrations are high but do not show a specific vertical distribution pattern. The CO concentrations in the main trench are horizontally attenuated away from this high-concentration zone. Three days after the blasts (Fig. 9), the high-concentration zone shrunk and CO © 2004 NRC Canada

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Fig. 9. Cross section A–A′ of the carbon monoxide concentrations observed in the monitoring system of the main trench 3 days after the blasting operations at house 2 at Rock Forest (see Fig. 6 for location of cross section).

diffused mainly to the A (northwest) side of the trench. A pumping well, for groundwater extraction, located in the main trench close to OP-1.5 may have contributed to the decrease of CO migration to the A′ side of the cross section. Groundwater was pumped at 20 L/min during the house 2 test to ensure that the deepest wells of the gas monitoring system were kept out of water. Also, a well cap made with polyethylene sheeting was put in place to minimize the air circulation from that well. In this cross section no trend in the vertical distribution of CO is observed, indicating that the density contrast between the interstitial air and the gas produced by the explosives has no significant influence on vertical CO migration. After this test a topographic survey was made of the blasted area (house 1, house 2, and the trench) and surrounding land to estimate the swelling of the rock created by the blasts. A three-dimensional map was produced with Surfer version 6 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 broken rock is estimated at 25%. Beauport house At Beauport the site of experimentation was located in fractured limestone rock covered with less than 1 m of sand. Three blasts were made in the same day. The monitoring of pressure showed that the blast-generated gas was first injected rapidly into the fractures already present in the rock, as shown by the positive pressure peak at 1.5 m (OP-1.5) from the perimeter of the house in Fig. 10. The generation of new fractures in the rock formation by the blast created voids under negative pressure that pull on the gas from the blast. This phenomenon was observed in the monitoring

Fig. 10. Pressures recorded as a function of time during blast B in two monitoring wells at Beauport.

wells at 1.5 and 5 m from the limit of the house but not at 20 m from the limit of the blasted house. The CO concentration measured in the monitoring system was less significant than in the tests at Rock Forest. During the Beauport test a large proportion of the gas generated by the blasts was seen to escape into the atmosphere because of the low confinement of the limestone by sand. The isoconcentration lines were drawn with Surfer version 7, and the interpolation was made by the modified Sheppard method because of the limited number of sampling points in this test. At t = 0, the migration of CO by advection in the ground was observed up to 5 m from the limit of the house (Fig. 11). Subsequent movement of the gas by diffusion or advection occurred to the south after 1 day, and the gas reached a distance of 15 m from the limit of the house. In the days that followed (t = 3 and 6 days), the CO concentrations decreased and the affected area reduced in size. The weak confinement of the © 2004 NRC Canada

Martel et al. Fig. 11. Carbon monoxide concentrations observed in the monitoring network after the blasts at the house at Beauport: (a) immediately after the explosions (t = 0 days), (b) at t = 1 day, (c) at t = 3 days, and (d) at t = 6 days.

blasts and the produced gases are probably responsible for these results. The blasts of the Beauport incident in 1995 were made under a paved road that helped confine the gases produced, and the carbon monoxide had migrated up to 12 m with concentrations higher than the those observed in this test. At the end of the test, the volume of broken rock and overburden above natural ground level was measured by excavating the material with a loader. The ratio of this volume to the volume of the initial blasted material (420 m3) gave a swelling of 36.8% and an adjusted porosity of the broken rock of 27%. The swelling and porosity for the Beauport test are the same as those measured for the Rock Forest tests, indicating the overall success of the blasts, even if an orange fume was escaping from the blasts.

Conclusion From the field tests conducted at Rock Forest and Beauport, some conclusions can be drawn. The structural geology of the rock formation (schistosity, family of joints, fractures) plays a role in the direction and distance of migration of gas in fractures generated when rock is blasted with explosives. Air permeability of fractured and broken rock is an important factor that controls the gas migration. The type of confinement of the rock (overburden type and thickness) can affect the quantity of gas migrating in the fractured rock. Significant concentrations of CO may persist in the fractured rock even 7 days after a blast if only natural dilution by interstitial air is occurring and no method for gas evacuation is applied. 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 (5–8 m). In trenches of broken rock (equivalent to fills under roads) the distance of CO migration by advection is greater (12–20 m). In the 2 to 3 days following the blasts, further CO migration up to 15 m was made by diffusion in the naturally occurring or induced fractures or up to 30 m in the trenches. The CO concentrations

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decreased after 2–3 days in the underground, and this was caused by dilution with noncontaminated interstitial air. From the review of CO poisoning cases it was found that the distance of migration of CO may reach 55 m if a conduit is present underground. Underground conduits broken by a blast, filling around underground conduits in a road 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 Quebec incidents. Based on the review of intoxication cases in Quebec and on the results of our field tests, it is recommended that a CO detector with an alarm be installed for a minimum period of 3 days after the blasts inside every house located within a radial distance of 30 m from a blast to warn people of significant CO concentrations infiltrating their house. Along a road with underground public services the distance for security control with CO detectors in houses may be increased to 75 m from the blast. In addition, special working procedures must be developed to minimize underground CO migration when blasting operations are located in the vicinity of enclosed spaces or buildings. To avoid CO intoxication of the population by fumes, blasting operations should be always done in accordance with the Institute of Makers of Explosives (IME) guidelines and recommended practices (IME 2001).

Acknowledgments We thank Dre Uta Gabriel and M. Thomas Robert for their help with the fieldwork and Jean-Michel Lemieux for the structural geology survey. 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 du Québec (MENVQ). We thank Dyno Nobel Inc. (M. Daniel Roy) for providing the explosives. We also acknowledge the technical support of M. Pierre Dorval (MTQ), M. Jean Pelletier (MENVQ), M. Pierre Tellier (Castonguay et Frères Inc.), and Marc Baril (IRSST). We also thank the other members of the technical provincial committee for their support and the two anonymous reviewers for constructive suggestions and corrections.

References Auger, P.L., Lévesque, B., Martel, R., Prud’homme, H., Bellemare, D., Barbeau, C., Lachance, P., and Rhainds, M. 1999. An unusual case of carbon monoxide poisoning. Environmental Health Perspective, 107: 603–605. Cooper, P. 1996. Explosives engineering, Wiley-VCH, New York. Dougherty, F., Loyle, F.T., Kunz, J., and Felleisen, L.K. 1990. An environmental case study involving carbon monoxide infiltration of nearby residences during sewer trenching. In Indoor Air ‘90, Proceedings of the 5th International Conference on Indoor Air Quality and Climate, Toronto, Ont., 29 July – 3 Aug. 1990. Vol. 3. Edited by D.S. Walkinshaw. Central Mortgage and Housing Corporation (CMHC), Ottawa, Ont. pp. 753–758. Health Canada. 1989. Direction générale de la protection de la santé, Rapport du comité consultatif fédéral provincial de l’hygiène du milieu et du travail. Directives d’exposition concer© 2004 NRC Canada

382 nant la qualité de l’air des résidences. Report EHD-TR 156. Health Canada, Ottawa, Ont. IME. 2001. Fumes from blasting operations. IME Guidelines and Recommended Practices, The Institute of Makers of Explosives (IME), Washington, D.C. Available from [accessed August 2001]. Johnson, P.C., Stanley, C.C., Kemblowski, N.W., Colthart, J.D., and Byers, D.L. 1990. A practical approach to the design, operation, and monitoring of soil venting systems. Ground Water Monitoring Review, 10(2): 159–178. Katsabanis, P.D., and Liu, Q. 1993. Calorimetric determination of the heat of detonation of commercial explosives. In Proceedings of the 9th Annual Symposium on Explosives and Blasting Research, San Diego, Calif. International Society of Explosives Engineers, Cleveland, Ohio. pp. 31–39. Martel, R., Trépanier, L., Boutin, L.-C., Lavigne, M.-A., Lévesque, B., Sanfaçon, G., Auger, P., Galarneau, L., and Brousseau, P. 2001. Carbon monoxide poisoning from blasting operations in construction works. In Proceedings of the 2nd Joint IAH–CNC and CGS Groundwater Specialty Conference and 54th Canadian Geotechnical Conference, Calgary, Alta., 16–19 Sept. 2001. Canadian Geotechnical Society, Alliston, Ont. pp. 1456–1465. Martel, R., Trépanier, L., Lavigne, M.-A., Lévesque, B., Sanfaçon, G., Brousseau, P., and Auger, P. 2004. Carbon monoxide poisoning associated with blasting operations close to underground enclosed spaces. Part 2. Special working procedures to minimize CO migration. Canadian Geotechnical Journal, 41: 383–391.

Can. Geotech. J. Vol. 41, 2004 Meredith, T., and Vale, A. 1998. Carbon monoxide poisoning. British Medical Journal, 296: 77–78. MSSS/MENVQ. 2001. Recommandations sur la problématique d’intoxication au monoxyde de carbone associée aux travaux à l’explosif en milieu habité. Ministère de la santé et des services sociaux (MSSS) and Ministère de l’environnement du Québec (MENVQ), Québec City, Que. NIOSH. 1998. Carbon monoxide poisoning and death after the use of explosives in a sewer construction project: Hazard ID 3. DHHS (NIOSH) Publication 98-122, National Institute for Occupational Health and Safety, Pittsburgh, Pa. Ontario Ministry of Health and Long-Term Care. 1995. Regional Municipality of Hamilton–Wentworth Teaching Health Unit: carbon monoxide incident in Hamilton–Wentworth. Public Health and Epidemiology Report (PHERO). Vol. 6. pp. 239– 241. Santis, L.D. 2001. A summary of subsurface carbon monoxide migration incidents. In Proceedings of the 27th Annual Conference on Explosives and Blasting Techniques, Orlando, Fla., 28– 31 Jan. 2001. Vol. 2. International Society of Explosives Engineers, Cleveland, Ohio. pp. 143–164. U.S. EPA. 2002. HyperVentilate. Office of Underground Storage Tanks (OUST), U.S. Environmental Protection Agency, Washington, D.C. Available from [accessed August 2001].

© 2004 NRC Canada