This document discusses tunneling safety guidelines and requirements. It describes several tunneling accidents that occurred between 1988-2013, including explosions from methane gas, collapses that killed workers, and flooding incidents. The document outlines OSHA requirements for tunneling projects, such as air monitoring, ventilation, emergency equipment, and safety training. It provides details on structural failures like rock falls, excessive deformations, and daylight collapses. Overall, the document aims to promote tunneling safety by documenting past accidents and outlining regulatory standards.

1. Tunneling Safety
johnanewquist@gmail.com
Draft 11 8 2015

2. 1988
• Milwaukee WI
• Methane gas was detected in a
40-foot-deep tunnel that was
under construction.
• The mining machine was
automatically shut down, and all
the employees were evacuated.
• Ten minutes later, three
employees entered the area to
determine if the atmosphere in
the tunnel was safe for reentry.
• An explosive mixture of methane
gas had developed in the air.
• Apparently, the grout pump
ignited the gas and caused an
explosion.
• The three employees were badly
burned, and they died of
asphyxiation due to overexposure
to carbon monoxide.

3. OSHA Specific Requirements
• Check-in/check-out.
• The employer shall maintain a
check-in/check-out procedure
that will ensure that above-
ground personnel can
determine an accurate count of
the number of persons
underground in the event of an
emergency.
• However, this procedure is not
required when the construction
of underground facilities
designed for human occupancy
has been sufficiently completed
so that the permanent
environmental controls are
effective, and when the
remaining construction activity
will not cause any
environmental hazard or
structural failure within the
facilities.
1926.800(c)

4. Safety Instruction
• All employees shall be
instructed in the recognition
and avoidance of hazards
associated with underground
construction activities including,
where appropriate, the
following subjects:
• Air monitoring:
• Ventilation:
• Illumination:
• Communications:
• Flood control:
• Mechanical equipment:
• Personal protective equipment:
• Explosives:
• Fire prevention and protection:
and
• Emergency procedures,
including evacuation plans and
check- in/check-out systems.
1926.800(d)

5. Emergency Provisions• Hoisting capability.
• When a shaft is used as a
means of egress, the
employer shall make advance
arrangements for power-
assisted hoisting capability to
be readily available in an
emergency, unless the
regular hoisting means can
continue to function in the
event of an electrical power
failure at the jobsite.
• Such hoisting means shall be
designed so that the load
hoist drum is powered in
both directions of rotation
and so that the brake is
automatically applied upon
power release or failure.
1926.800(g)(1)

6. Emergency Provisions• Self-rescuers.
• The employer must provide
self-rescuers approved by the
National Institute for
Occupational Safety and
Health under 42 CFR part 84.
• The respirators must be
immediately available to all
employees at work stations
in underground areas where
employees might be trapped
by smoke or gas.
• The selection, issuance, use,
and care of respirators must
be in accordance with 29 CFR
1926.103.
1926.800(g)(2)

7. Emergency Provisions
• Designated person.
• At least one designated
person shall be on duty
above ground whenever
any employee is working
underground.
• This designated person
shall be responsible for
securing immediate aid
and keeping an accurate
count of employees
underground in case of
emergency.
• The designated person
must not be so busy that
the counting function is
encumbered.
1926.800(g)(3)

8. Emergency Provisions• Emergency lighting.
• Each employee
underground shall
have an acceptable
portable hand lamp or
cap lamp in his or her
work area for
emergency use, unless
natural light or an
emergency lighting
system provides
adequate illumination
for escape.
1926.800(g)(4)

9. Emergency Provisions
• Rescue teams.
• On jobsites where less
than 25 employees work
underground at one
time, the employer shall
provide (or make
arrangements in
advance with locally
available rescue services
to provide) at least one
5-person rescue team to
be either on the jobsite
or within one-half hour
travel time from the
entry point.
1926.800(g)(5)(ii)

10. Hazardous
Classifications
• Potentially gassy operations.
• Underground construction operations
shall be classified as potentially gassy if
either:
• Air monitoring discloses 10 percent or
more of the lower explosive limit for
methane or other flammable gases
measured at 12 inches (304.8 mm) to +
or - 0.25 inch (6.35 mm) from the roof,
face, floor or walls in any underground
work area for more than a 24-hour
period: or
• The history of the geographical area or
geological formation indicates that 10
percent or more of the lower explosive
limit for methane or other flammable
gases is likely to be encountered in such
underground operations.
1926.800(h)(1)

11. Air Quality and
Monitoring.
• Where this paragraph requires monitoring of
airborne contaminants "as often as necessary,"
the competent person shall make a reasonable
determination as to which substances to monitor
and how frequently monitor, considering at least
the following factors:
• Location of jobsite: Proximity to fuel tanks,
sewers, gas lines, old landfills, coal deposits, and
swamps;
• Geology:
• History: Presence of air contaminants in nearby
jobsites, changes in levels of substances
monitored on the prior shift; and
• Work practices and jobsite conditions: The use of
diesel engines, use of explosives, use of fuel gas,
volume and flow of ventilation, visible
atmospheric conditions, decompression of the
atmosphere, welding, cutting and hot work, and
employees' physical reactions to working
underground.
1926.800(j)(1)(i)(B)

12. Air Quality and Monitoring.
• Recordkeeping.
• A record of all air quality
tests shall be maintained
above ground at the worksite
and be made available to the
Secretary of Labor upon
request.
• The record shall include the
location, date, time,
substance and amount
monitored.
• Records of exposures to toxic
substances shall be retained
in accordance with 1926.33
of this chapter.
• All other air quality test
records shall be retained
until completion of the
project.
1926.800(j)(3)

13. Ventilation• Fresh air shall be supplied to all
underground work areas in
sufficient quantities to prevent
dangerous or harmful
accumulation of dusts, fumes,
mists, vapors or gases.
• Mechanical ventilation shall be
provided in all underground work
areas except when the employer
can demonstrate that natural
ventilation provides the necessary
air quality through sufficient air
volume and air flow.
• A minimum of 200 cubic feet of
fresh air per minute shall be
supplied for each employee
underground.
1926.800(k)(1)

14. Fire Control
• Flammable or combustible
materials shall not be stored
above ground within 100 feet
(30.48m) of any access opening
to any underground operation.
• Where this is not feasible
because of space limitations at
the jobsite, such materials may
be located within the 100-foot
limit, provided that:
• They are located as far as
practicable from the opening;
and
• Either a fire-resistant barrier of
not less than one-hour rating is
placed between the stored
material and the opening, or
additional precautions are taken
which will protect the materials
from ignition sources.
1926.800(m)(7)
Oxygen and acetylene stored together
is a violation.

15. Fire Control
• Lighting fixtures in
storage areas, or within
25 feet (7.62 m) of
underground areas
where oil, grease, or
diesel fuel are stored,
shall be approved for
Class I, Division 2
locations, in accordance
with Subpart K of this
part.
1926.800(m)(9)

16. Portal Areas
• Competent persons
conducting such
inspections shall be
protected from loose
ground by location,
ground support or
equivalent means
1926.800(o)(3)

17. Portal Areas
• Suitable protection
shall be provided for
employees exposed to
the hazard of loose
ground while installing
ground support
systems.
1926.800(o)(3)

18. OSHA Citations
• Fall Protection

19. OSHA Citations
• Fall Protection

20. OSHA Citations
• Ladder

21. OSHA Citations
• Unapproved rigging

22. OSHA Citations
• Ladder

23. OSHA Citations
• Fall Protection

24. OSHA Citations
• Lighting

25. OSHA Citations
• Fall

26. OSHA Citations
• Rigging
• no capacity marked

27. OSHA Citations
• GHS
• Spill Control

28. OSHA Citations
• Fall

29. OSHA Citations
• Homemade drum
carrier

30. Structural Issues
• Rock Fall - Fall of rock blocks of major
dimensions. The different
mechanisms involved are wedge or
planar failure..
• Collapse Heading collapse - failure of
the heading / lining failure .
• Daylight Collapse Heading collapse -
lining failure of the heading that
reaches the surface creating a crater.
• Excessive Deformation - Excessive
deformations inside the tunnel or at
the surface. This can occur for
example due to deficient design,
construction defects and/or due to
particular type of terrains such as
swelling and squeezing ground,
which had not been predicted.
• Flooding - Comprises cases where the
tunnel was invaded by large
quantities of underground water.
• Rock Burst - Spalling Overstressing of
massive or intact brittle rock, i.e. the
stresses developed in the ground
exceed the local strength of the
material. It can cause spalling or in
the worst cases sudden and violent
failure of the rock mass
• Portal failure - Particular locations of
a tunnel, where there is a lower
• Shaft failure - resistance of ground
mass and/ or concentration of
stresses.
• Other - Other types of collapse that
include slope failures, etc

31. Structural Failures

32. Rock Fall
• Rock fall blocking the
TBM at the Covao
tunnel in 2006 (Madeira
Island, Portugal)

33. Collapse
• The large collapse occurred in front of the face and stopped the
cutter head rotation, creating a cavern more than 10 m high over
the TBM.
• This was an example of a full collapse of the face.

34. Collapse• Wienerwald Austria
• In this case, ground water
led to de-compaction and
bulking of the sandstone,
which caused the shear
strength to decrease.
• From this it follows that
the strength of rock was
very low and ground
pressure loaded the
temporary shotcrete
shell, which was not
designed for that kind of
high loading.
• Therefore the shotcrete
shell spalled off and the
lattice girder was
deformed.

35. Daylight Collapse
• These are collapses that
reach the surface
creating a crater.
• Munich Metro in 1994
• No deaths

36. Daylight Collapse
• Sao Paulo Brazil 2007
• 7 deaths
• Open face tunnelling is cheap.
• New Austrian Tunnelling
Method (NATM) is much less
expensive than a soft ground TBM,
but much less safe
• A combination of explosives and
mechanical excavation techniques
were being used.
• 'The top heading of the failed tunnel
was fully excavated in rock.
• There was approximately 6m of rock
above the tunnel,
• Support consisted of steel arch
girders at 800mm centres, and
350mm thick steel fibre reinforced
sprayed concrete.
• 'The vertical displacements measured
at the tunnel crown were in the
range of 3mm when the top heading
excavation was completed.
• Two to three days before the
accident, the rate of those
displacements increased, and they
reached 15mm to 20mm.

37. Daylight Collapse
• 2003: Shanghai's underground
Pearl Line, China
• $80 million
• The accident occurred in a cross
passage between the two parallel
tunnel tubes that had already
been driven using earth-pressure-
balance TBMs.
• Shortly before the cross passage
broke through, at a depth of
about 35 m, massive inrushes of
material and water occurred,
which the tunnel crew was not
able to bring under control and
which resulted in a large scale
subsidence at the

38. Daylight Collapse
• South Korean city of Taegu
on 22 January 2001
• Failure of a diaphragm wall.
• Part of a station excavation
pit caved in, burying a bus,
killing three passengers and
damaging neighboring
buildings.
• The accident was caused by
a load not considered in the
design phases and due to
unforeseen soil conditions.
• $24 million

39. Flooding
• It is during the construction
of underwater tunnels that
largest scale floodings have
occurred.
• The ground under rivers,
channels and bays is
normally weak and under
high water pressure and
therefore extreme safety
measures and efficient
protection against water
inflow are normally
required.

40. Flooding
• Seikan tunnel is a 53.85 km long
railway tunnel in Japan
• 1963-1976
• Four floods
• 23 deaths
• Leaks and soft rock
• TBM not practical due to the
various types of soils.
• Drill and pound.
• A great majority of the tunnel
crosses heavily fissured rock (9
large shear zones). The sea and
underground water penetrate
into these zones and the
maximum water pressure is
about 25 MPa

41. Flooding
• Lausanne, Switzerland
• A huge amount of soil
and water (1400m3)
displaced into the
tunnel and caused
extensive damage

42. Rockburst/Spalling
• This type of event is
caused by the
overstressing of massive
or intact brittle rock, i.e.
the stresses developed in
the ground exceed the
local strength of the
material.
• It can cause spalling or in
the worst cases sudden
and violent failure of the
rock mass

43. Excessive Deformation
• These are cases where
excessive deformations
occur inside the tunnel or at
the surface but an actual
total collapse does not
happen.
• This can occur for example
due to deficient design,
construction defects and/or
due to particular type of
terrains such as swelling
and squeezing ground,
which had not been
predicted.

44. Excessive Deformation
• Rotarelle to San Vittore
tunnel, Italy 1991
• After 650m of excavation,
enormous ground pressures
caused cracking of the
shotcrete, buckling of the
steel arches after a few
hours, and deformations of
200 mm in 24h and 400 mm
after 12 days
• The deformations were
caused by swelling clay
filling of the rock.

45. Excessive Deformation
• Squeezing is
characterized large
time-dependent
convergence during
tunnel excavation.
• Failure of the support
system.
• Inadequate support for
such ground conditions.
1999: Bolu Tunnel, Turkey
An earthquake caused the collapse of a
section of the Bolu tunnel, part of the
Anatolian highway, even though the
tunnel had been designed to withstand
earthquakes. $115 million loss

46. 1908-1913
• Lotschberg tunnel
• Switzerland
• Use of timber supports
after collapse killed 25
in 1908

47. Hawks Nest WV
• 1930s
• A simple diversion tunnel for
the New River in West Virginia
• After workers discovered silica
in the rock they were told to
mine it as a by-product of
tunnel construction, however,
they were never given any
masks or protective gear.
• Hundreds of workers
developed silicosis due to the
long-term exposure of silica
dust in their lungs.

48. New York City Third Water Tunnel
• The largest
infrastructure project in
New York state history
is currently tunneling
below New Yorker's feet
to provide a third
connection to the
upstate water supply

49. St. Gotthard Road Tunnel, 1969-1980
• At the time it was
completed, this 10-mile
tunnel in Switzerland was
the longest road tunnel in
the world.
• Tragically, 19 people died
working on the tunnel—
which was created to
connect central Switzerland
with Milan, Italy through
the Alps, providing a faster
and safer year-round
alternative to the winding
Gotthard Pass.

50. Big Dig Ceiling
Collapse
• July 10, 2006
• Concrete ceiling panel and debris
weighing 26 tons fell in Boston's
Fort Point Channel Tunnel
• The panel fell on a car killing a
passenger and injuring the driver.
• The collapse of the ceiling
structure began with the
simultaneous creep-type failure
of several anchors embedded in
epoxy in the tunnel's roof slab.
• Each of the panel's intersecting
connection points consists of
several individual bolts anchored
into the roof slab concrete.
• The failure of a group of anchors
set off a chain reaction which
caused other adjacent connection
groups to creep then fail

51. Big Dig Ceiling
Collapse
• Not only were the bolts too short,
but the epoxy used to glue the
bolts into the concrete was not
up to standard.

52. Big Dig Ceiling
Collapse
• Major cause of the collapse to
"epoxy creep“
• On August 8, 2007, a Suffolk
County Grand Jury indicted epoxy
company Powers Fasteners, Inc.,
on one charge of involuntary
manslaughter, with the maximum
penalty in Massachusetts being a
fine of one thousand dollars.[10]
• The epoxy used in the D Street
portal that failed cost $1287.60.
The cost to redesign, inspect, and
repair all of the tunnels after the
collapse was $54 million.[1

53. 2004: Circle Line, Singapore
• Collapse of a construction
pit resulted in the death
of four workers plus the
collapse of an adjoining
highway.
• It eventually was found
that the most apparent
cause of the collapse was
that the retaining wall
could not handle the
stress of holding up the
tunnel, forcing it to give
way.

54. 1994: Heathrow Express Link
• London
• Three tunnels forming part of the
Heathrow Express Link,
connecting central London and
Heathrow Airport, caved in and
took several buildings with them.
• $141 million
• According to the HSE, a chain of
events led directly to the
collapse.
• This included a failure to check
substandard construction over a
period of some three months,
pressure grouting that damaged
the tunnel plus inadequately
executed repairs some two
months before the collapse.

55. 1994/95: Metro
• Taipei, Taiwan
• When the Metro was being built
in Taiwan in the 1990s, several
serious tunnel collapses occurred,
causing major property damage
to adjacent buildings as well as
serious liability losses.
• $41 million
• Difficult geology, with fractured
rock and massive inflows of
water, countless cave-ins, mud
and rock slides caused by massive
inflows of groundwater.
• Eleven people were killed in the
accidents.

56. 1999: Tunnel in Hull
• England
• During one of the tunnel
drives for a 6.5 mile
underground sewer in Hull,
England, a deformation in the
floor of the tunnel shell led to
flooding of the tunnel and
subsidence at the surface,
resulting in substantial
damage to buildings, roads
and utility lines.
• Machines and the tunnel were
abandoned.
• $55 million

57. XIAN Subway
• 2013 China
• At least two are dead after an
accident at a subway
construction site in Xi’an,
Shaanxi province this morning.
• At around 2:40 am, a tunnel
caved in as nine workers were
in the midst of building Line 3.
• Four have been rescued, but
of the five that were buried,
two have been found dead
while the other three are still
missing

58. Dec 2014
• Vietnam
• Rescuers have created a
16 cm-wide access hole
to the location where
12 workers have been
trapped inside a
collapsed tunnel section
at a hydropower plant
in the Central Highlands
province of Lam Dong
They may have assumed that the dry
season had come and it was safe to
dig, but this year the rainy season
lasted too long.
With heavy rains making the
foundation weak, sinkages occurred
in the tunnel.
And given the Central Highlands’
geological formations, digging up a
big rock may lead to the whole
tunnel’s collapse.

59. 2000
• Dulles Airport
• One dead
• At the time of the accident, about
700 ft of the approximately 40 ft
wide by 16 ft tall tunnel had been
excavated.
• Employee #1 was using a
shotcrete hose to spray the side
walls at the tunnel's earthen face
when the top and side of the
tunnel collapsed.
• In the week before the tunnel
gave way, there were three
partial collapses, each increasing
in severity

60. July 2015
• A construction worker
who was killed when a
winch he was operating
broke loose from its
anchor at a tunneling
site in the High Desert
has been identified as
David Padilla, 38, of
Pahrump, Nevada.

61. February 2015
• Seattle WA
• WSDOT now says five
workers were installing
rebar for a concrete
wall at the tunnel’s
north portal work zone.
• The wall of rebar gave
way, injuring four of the
five workers.

62. 2013
• Sunol CA
• On August 22, 2013, Employee
#1, was working on a pipeline
project.
• A piece of cement grout
approximately 1.5 feet by 1.5
feet by 6 feet long fell out of
the tunnel face approximately
3 feet above the invert.
• The cement pinned Employee
#1's leg against a roadheader.
• Employee #1 sustained
bruising/contusions/abrasions.

63. 2013
• On June 17, 2013, an employee was working as a heavy equipment
mechanic for a bridge, tunnel, and highway construction firm.
• He was on a segment build deck, assembling a tunnel boring machine.
• He fell off the deck, falling a distance of 10 feet.
He sustained a strain or sprain in his left ankle

64. TBM Closed Mode

65. 2011
• Webster NY
• Employee #1, a locomotive
operator, was moving muck
buckets and equipment to the
head section of a tunnel.
• When the operator reached
the end of the tunnel, the
locomotive failed to stop and
Employee #1 was crushed
between the locomotive and
the conveyor on the tunnel
boring machine.
• Employee #1 was killed.

66. 2011
• Woodland CA
• Employee #2, a laborer, noticed a
hole in a material chute in the No.
196 tunnel conveyor system.
• Employee #1 was joined by Employee
#2 in the reclaim tunnel to schedule
and plan a repair operation.
• As the two Employees exited the
tunnel and walked away from the
overhead No. 196 Conveyor, a 10
pound rock fell off the conveyor
striking Employee #1 in the head and
Employee #2 in the back, knocking
both employees to the ground.
• Employee #1 was knocked
unconscious and landed on top of
Employee #2.

67. 2009
• Kermit, WV
• Employee #1 was engaged in the
preparations for raising the
height of a tunnel liner.
• Employee #1 bored several holes
for taking core samples and
pictures were taken.
• Employee #1 entered the tunnel
through the west portal entrance,
with his excavator equipped with
a hoe ram.
• After reaching the necessary
work station, Employee #1 began
hammering out the center part of
the tunnel's liner to remove it.
• About 30 minutes following the
start of work, a section of the
roof fell, crushing and killing
Employee #1.

68. 2009
• Alexandria VA
• Employee #1 was working in a
subway tunnel for the
Washington Metropolitan Area
Transit Authority.
• A train passed by the location
where Employee #1 was standing.
• Coworkers reported that they
heard a noise and then the train
stopped.
• When the coworkers found
Employee #1, it was apparent
that he had been struck by the
train and suffered trauma to his
head and one leg.

69. 2009
• Cartersville GA
• Employee #1 was packing
straw around the east end of
the tunnel plate.
• The top, unprotected end of
the tunnel collapsed and
buried Employee #1's head
and neck in mud on top of the
tunnel plate.
• Coworkers attempted to
rescue Employee #1; however,
they were unsuccessful and he
was pronounced dead at the
site.

70. 2008• Employees #1 though #5, were
repairing the floor of the south
bypass conduit water tunnel
located under Lake Las Vegas in
Henderson, Nevada.
• The tunnel was two miles long
and seven feet in diameter.
• They were preparing to pour
concrete on the tunnel floor.
• Two workers activated the
ventilation fan from outside.
• Concrete was carried in eight
buggy carts pulled by bobcat.
• Behind them, the mechanic and
Project Superintendent followed
on a propane-operated golf cart.
• Around 10:00 a.m., these
employees arrived at the work
location and found that the
mechanical ventilation fan had
been shut down.
• Several unsuccessful attempts
were made to start the fan.
• The Project Superintendent and
foreman decided that work would
continue, after measuring the natural
air flow using a handheld Mini
Thermo-Anemometer by Extech
Instrument.
• At 11:15 a.m., the foreman radioed
from inside tunnel that employees
were experiencing difficulty
breathing, chest pains, and fatigue.
• The project superintendent sent golf
carts and removed all employees
from the tunnel about 12:16 p.m.
• Employees #1 through #5 were
treated for asphyxia and carbon
monoxide poisoning at University
Medical Center (UMC) in Las Vegas
and St. Rose De Lima in Henderson

71. 2007
• Houston TX
• Employee and five coworkers were
working attempting to install a 60-in.
by 10-ft by 0.5-in. steel pipe casing
for the 42-in. regional main water
line.
• The site was comprised of a 60-ft by
40-ft shaft which led down to a
tunnel, which had already pushed
the 60-in. steel pipe approximately
120-130-ft laterally under the
Cypress Creek.
• The employee was cleaning the
excess dirt from the 60-in. pipe as the
pipe was hydraulically pushed inside.
• A breach occurred, immediately
filling the tunnel and the shaft with
water.
• All of the coworkers were able to
escape except the employee.

72. 2005
• Minneapolis MN
• At approximately 7:00 a.m. on
September 6, 2005, Employee
#1 entered the work area on
the fifth floor of the project.
• Employee #1 was walking
through tunnel forms to
prepare the forms for a
concrete pour.
• As Employee #1 walked
toward the end of the form
inspecting his work, he
stepped through a floor hole
and fell approximately 45 ft to
his death.

73. 2000
• Chanilly VA
• The 27 ft deep passenger
walkway tunnel was being
constructed from one terminal to
another.
• At the time of the accident, about
700 ft of the approximately 40 ft
wide by 16 ft tall tunnel had been
excavated.
• Employee #1 was using a
shotcrete hose to spray the side
walls at the tunnel's earthen face
when the top and side of the
tunnel collapsed.
• Fire and emergency services were
called but they were unable to
rescue Employee #1.