Climbing, Lifting, Rigging & Hoisting Flashcards
1
Q
Why is wire rope preferable to chain?
A
It is strong and unlike chains, gives good warning of failure when it is defective.
2
Q
What are the different grades of wire rope and what are their breaking loads?
A
Traction grade - breaking load of 80 - 90 tons per square inch.
Special improved plow grade - breaking load of 120 - 130 tons per square inch.
Improved plow quality grade - breaking load of 110 - 120 tons per square inch.
3
Q
What grade of wire rope is most commonly used?
A
Improved plow quality grade.
4
Q
What do the terms lay and lay length refer to?
A
Lay - refers to the direction in which the strands of a rope are twisted together.
Lay length - refers to the distance along the rope in which a strand makes one revolution.
5
Q
When are independent wire rope cores (lWRC) or wire rope cores (WRC) used?
A
When wire rope is subject to sudden heavy loads, crushing, or heat.
6
Q
Right regular lay is the most common wire rope. How is it made?
A
It consists of a number of wires twisted to the left around a small core to form each of six strands. These strands are then twisted to the right around the main core to form the final rope.
7
Q
How is Lang’s lay wire rope made?
A
It has the wires and strands twisted in the same direction. The core design is the same as that of the regular lay.
8
Q
What are some of the properties of preformed wire ropes?
A
They do not fly apart when cut.
They can be spliced without seizing/whipped (binding).
When wires break, they lie flat in
position on the rope.
9
Q
How is wire rope measured?
A
Across its greatest diameter.
10
Q
What must be done when a kink is found in a wire rope?
A
Once a kink has been made in a wire rope, the damage is permanent. A weak spot remains no matter how well the rope is straightened.
11
Q
When inspecting sheaves for wire ropes, what must be inspected?
A
- Check flanges for wear.
- The sheave groove should support the rope over 135- to 150-degrees of rope circumference.
12
Q
What are the frictional losses sheaves experience for different types of bearings?
A
Roller bearing - 3% loss
Bronze bushing - 5% loss
Plain bearing - 10% loss
13
Q
As a rule-of-thumb, the minimum sheave diameter should be how many times larger than the rope diameter?
A
20 times.
14
Q
When winding a wire rope onto a drum, how does fleet angle effect rope life?
A
An excessive fleet angle will cause severe abrasion on the rope as it winds onto the drum. This condition can severely shorten rope life.
15
Q
To ensure proper wire rope lubrication, what must be done?
A
- Ensure that the rope is clean and dry before the lubricant is applied.
- Apply light oils by brushing, running the rope through an oil bath, spraying, drip method or mechanical force feed.
- Apply medium- or heavy-weight lubricants warm. Apply them by brush or by running the rope through a funnel containing the lubricant.
16
Q
When unwinding rope from a spool why must you not rope of the side of the spool a wrap at a time?
A
This often results in kinks.
17
Q
What is the correct way to take a length of wire rope from a spool?
A
Rotate the spool on a spindle or turntable, or roll the spool along the floor.
18
Q
How is the rule of hand used when winding wire rope on a drum?
A
- The right hand represents right-lay rope.
- The left hand represents left-lay rope.
- The index finger shows the approach of the ropes.
- The position of the back of the hand indicates whether the rope is overwound or
underwound. - The position of the thumb shows where the rope is attached to the drum.
19
Q
How is a natural fiber rope constructed?
A
The usual method of construction for fiber rope is reverse twisting.
* Fibers from 6 to 20 feet long are combed to bring them parallel to each other.
* A definite number of fibers are right-hand twisted to form a yarn.
* A number of yarns are then left-hand twisted into a strand.
* Finally. three or four of these strands are right-hand twisted to form the rope.
This produces a right lay rope.
20
Q
How does the diameter of a natural or synthetic rope impact its ability to handle a load?
A
The diameter of natural fiber rope must be larger than synthetic rope to handle the same load.
21
Q
How is fiber rope size measured?
A
Ropes up to one inch are measured by their diameter.
Ropes over one inch are measured by their circumference.
22
Q
What is a new ropes working strength?
A
For new rope the working strength is 1/5 of
its breaking strength.
For a used rope, increase this safety factor.
23
Q
What type of knot is in the image?
A
Overhand knot.
Frequently used as a stopper at the
end of a rope.
24
Q
What type of knot is in the image?
A
Figure-of-eight knot.
Used at the end of a line to prevent the end from slipping through a fastening or loop
in another line.
25
What type of knot is in the image?
Square or reef knot.
Used for tying together two lines of the same size so that they will not slip.
26
What type of knot is in the image?
Bowline.
Commonly used for forming a loop in the end of a line. It is easy to tie and untie, will not slip. and can be used to secure loads without crushing them.
27
What type of knot is in the image?
Bowline on the bight.
Used for putting a non-slip loop anywhere
between the ends of a rope.
28
What type of knot is in the image?
Round turn and two half hitches.
One of the most efficient and most used knots. It can be used wherever a line must be made fast.
29
What type of knot is in the image?
Becket Hitch.
Used for making a line fast to the becket of a block or to a ring.
30
What determines chain size?
The diameter of the wire or rod determines the chain size.
31
What grade of chain can be used for overhead hoisting?
Grade A or at least Grade 80 chain.
32
What should chains used as slings be supplied with?
A master ring at one end and a hook at the other.
33
After how much wear should a chain no longer be used for hoisting?
Chains less than 1-inch - 5% of the link diameter.
Chains greater than 1-inch - 10% of the link diameter.
34
What is the efficiency of a poured zinc (spelter) drop-forged socket?
When properly attached, they are 100% efficient.
35
What is the efficiency of cappel sockets?
When properly installed, 100% efficient.
36
What is the efficiency of a wedge socket?
Only 70% efficient.
37
In order to install a wedge socket properly, what must be the amount of rope left on the dead end, and how must the clip be fastened to the dead end?
6- to 9-inches of rope left above the wedge on the dead end.
The clip must not attach to the live end of the rope, only the dead end.
38
What is the efficiency of swaged sockets?
Properly made they provide 100% efficiency.
39
When should a swaged socket be condemned?
If only one broken wire is seen.
40
Why is it important to have a thimble when making an eye?
Thimbles maintain rope strength and reduce wear.
Without a thimble the eye loses 10% efficiency.
41
When installing cable clips what is the formula to determine how many to use?
Number of clips = (Dia of rope x 3) + 1
*The answer is rounded up.
42
What is the formula to determine the spacing of of the clamps on the wire rope?
Spacing of clips = Diameter of rope x 6
43
What should be the distance from the rope end to the first cable clamp?
6 or 7 rope diameters.
44
How efficient are cable clips when installed properly?
They have 80% of the rope strength.
45
By how much can improper application of even one clip effect efficiency of the connection?
It can reduce it by 40%.
46
What is the order of applying clips to a rope?
1. Apply the first clip at the end of the rope.
2. Apply the second clip near the hook end.
3. Apply all other clips in the middle.
4. Apply tension and tighten clips.
47
How do you use clips to connect two ropes end-to-end?
Use the clips to form an eye
(with thimble) in each length and connect the eyes with a shackle.
48
When inspecting a hook for wear, what are three things to inspect?
1. Look for wear in the saddle of the hook.
2. Look for cracks, severe corrosion and twisting of the hook body.
3. Measure the throat opening. If there is any evidence of throat opening or distortion, destroy the hook.
49
How does the load center on the hook effect its ability to carry the rated load?
Balance load - can carry 100% of rated load.
1/2 off center - can carry roughly 80% of rated load.
Point loading - can carry roughly 40% of rated load
50
How are shackles sized?
By the diameter of the steel in the bow section.
51
How much must a shackle be worn before it is destroyed?
10% wear.
52
Why should you not angularly load a plain (shoulderless) eye bolt?
As soon as it is loaded at an angle the safe working load is severely reduced and is can break.
53
To make sure eye bolts with a shoulder are in safe working condition during use, what four things must be addressed?
1. Make sure the shoulder firmly contacts the working surface. Use washers if needed.
2. The nuts are properly torqued.
3. The tapped hole for the bolt has a minimum depth of 1.5 times the bolt diameter.
4. The threads in the hole and on the bolt are in good condition.
54
When using an eye bolt to lift, how must the be applied to the eye bolt?
Always apply loads to the plane of the eye or the eye might fail.
55
When lifting with eye bolts, what angle must the shackle be at in relation to the work surface?
Ensure the angle is above 45-degrees.
56
If eye bolts cannot be aligned with each other, what must be used to align them so the eye can be tightened to the correct orientation?
Insert thin washers or shims under the collar.
57
If a turnbuckle is to be used where there is vibration, what must be done?
It is extremely important to lock the frame to the end fittings to prevent it from turning and loosening. Use lock wire to secure the turnbuckle.
58
When are spreader beams used?
Spreader beams are usually used to support long loads during lifts. They remove the risk of the load tipping. sliding or bending. They also remove the possibility of low sling angles and the tendency of the slings to crush the load.
59
What are equalizer beams used for?
Equalizer beams are used to equalize the load on sling legs and to keep equal loads On dual hoist lines when making tandem lifts.
60
What happens to the load capacity of beams with multiple attachment points if the space between the points is doubled?
The capacity of the beam is halved.
61
Up to 7-30
Up to 7-30
62
Start on 7-36
Start on 7-36
63
By how much can a knot reduce the breaking strength of a fiber rope?
By up to 50%.
64
By how much do correctly attached cable clips to a wire rope reduce its breaking strength?
By 20%.
65
What formula is used to determine the approximate SWL of a wire rope in tons?
SWL in tons = D^2 × 8 (D = diameter of wire rope in inches).
66
What is the formula for calculating the safe working load of a single vertical rope?
SWL = (# of 3/8" sections x 1 ton) + (# of 1/8" sections x 1 ton)
67
What is the formula for calculating the safe working load of a basket hitch?
SWL = SWL1 x (H/L) x 2
Where:
SWL1 = safe working load for a vertical rope of a certain diameter
H = distance between hook and load
L = length of sling legs
68
What is the formula for calculating the safe working load of a two-leg bridle hitch?
SWL = SWL1 x (H/L) x 2
Where:
SWL1 = safe working load for a vertical rope of a certain diameter
H = distance between hook and load
L = length of sling legs
69
In a bridle hitch what formula is used to determine the sling tension?
Sling tension = (W/N) x (L/V)
Where:
W is the weight of the load.
N is the number of slings. This value can never be more than two.
L is the length of the slings.
V is the vertical height from the load to the sling’s attachment point.
70
What is the formula for calculating the safe working load of a choker hitch with an angle over 45-degrees?
SWL = SWL1 x 3/4
Where:
SWL1 = safe working load for a vertical rope of a certain diameter
71
What is the formula for calculating the safe working load of a choker hitch with an angle of 45-degrees or less?
SWL = SWL1 x (A/B)
Where:
SWL1 = safe working load for a vertical rope of a certain diameter
A = distance between hook and load
B = length of sling legs
72
What is the formula for calculating the safe working load of a pair of choker hitches?
SWL = SWL1 x (A/B) x (H/L) x 2
Where:
SWL1 = safe working load for a vertical rope of a certain diameter
A = distance between hook and load at the choker hitch
B = length of sling legs at the choker hitch
H = distance from main hook
L = length of sling from main hook to choker hitch
73
What is the formula for calculating the safe working load of a double basket hitch?
SWL = SWL1 x (H/L) x 4
Where:
SWL1 = safe working load for a vertical rope of a certain diameter
H = distance from the hook to the load
L = length of the sling
74
What are the essential parts of any block?
The shell, the sheaves, a center pin, the straps, and a becket.
75
Why should you never run fiber ropes over sheaves that have been used with wire ropes?
Rapid rope damage will result.
Fibre-rope sheaves are NOT used with wire
rope because their diameters are too small.
76
What are travelling blocks and standing blocks?
A travelling or fall block is a block that is attached to the load being lifted or moved. It
moves with the load.
A standing block is a block that is fixed to a stationary object. This object takes the force of the loading.
77
How does snatch block rope angle effect snatch block load?
A snatch block load of 2000 lbs at 0-degrees would would be 760 lbs at 135-degrees.
Snatch block load decreases with increased rope angle.
78
Why should you never incline the legs of a double basket hitch less than 60-degrees to the horizontal?
To prevent the legs from sliding towards each other.
79
What type of sling is used to secure loose loads?
The double basket hitch.
80
What is another type of sling that can be used to secure long, loose loads?
The double choker hitch or the double-wrap choker hitch.
81
What are the safe working loads for loads, people, and elevators?
Loads - 1/5 of the breaking strength
People - 1/10 of the breaking strength
Elevators - 1/20 of the breaking strength
82
What are two types of blocks that are suited for high speed applications and heavy loads?
Crane and hook block and wire rope block.
83
What is the difference in durability between crane and hook blocks and wire rope blocks?
Wire rope blocks are not intended to withstand the heavy service and abuse expected of crane and hook blocks.
84
What type of rope is a tackle block used with?
Fiber ropes.
85
What type of chain hoists should be used when hoisting loads in oil and why must they be used?
Use screw-geared or differential hoist.
This is because for spur-geared and lever operated, the oil can foul the load brake.
86
What are the effects of sling angle on sling load?
For a 1000 lbs load, two slings at 90-degrees would both feel a load of 500 lbs.
As this angle is decreased to 30-degrees, both slings feel a load of 1000 lbs.
87
What is the recommended safe lifting angle for slings?
The recommended safe lifting angle for sling legs is 60°.
88
What is the shallowest sling angle allowed when using an eye bolt?
45-degrees.
89
How does eye bolt safe working load change as sling angle is changed?
Safe working load goes down as sling angle decreases, until 45-degrees is reached. At 45-degrees the lift should not be performed.
90
What are the two types of hooks that do not require a safety latch?
Grab chain hooks and sorting hooks.
91
What is an important attachment to allow wire ropes to spin freely so that stress is taken off the line?
Swivels.
92
In a block, what is used to transfer the load from a rope to the center pin and straps?
The sheaves or pulleys.
93
How many times the safe working limit (SWL) of the sling material is a single vertical hitch rated for?
1 times the SWL of the sling material.
94
How many times the safe working limit (SWL) of the sling material is a basket hitch rated for?
2 times the SWL of the sling material.
(Only if sling legs are vertical, load is circular, and its e is 20 or more times the diameter of the wire rope sling)
95
How many times the safe working limit (SWL) of a single vertical hitch is a choker hitch rated for?
3/4 the SWL of a single vertical hitch.
96
When inspecting turnbuckles for damage what should be inspected?
Check for cracks and bends.
Check for thread damage and bent rods.
97
What are two of the wear conditions of a sheave with regards to rope and groove?
1 .Worn rope, worn groove.
2. New rope, worn groove.
98
What value of a particular chain refers to the maximum load that can safely be applied to a straight length of chain?
Working load limit.
99
What value is a comparison between a chain's minimum ultimate load and working load limit?
Chain safety factor.
100
For a chain's safety factor, the minimum ultimate load is how many times the chains working load?
A safety factor or 4 to 1.
101
How much is a strand of a wire rope allowed to wear before it needs to be replaced?
1/3 its original diameter.
102
How must a chain sling be inspected and what is the maximum amount of wear allowed in one link?
Every link is to be inspected and the sling discarded if wear exceeds 10% of the diameter of the link.
Other damage could be if the links show signs of cuts, nicks, burns, or corrosion pitting; or if any of the links are bent or twisted.
103
What material are synthetic web slings made more frequently from?
Nylon.
104
What happens to the sling if a steel wire mesh sling is subjected to shock loading?
It will not absorb the shock load, but rather become damaged or break.
105
Using the rule of thumb, determine the SWL of a wire rope with a diameter of 1-1/2 in.
D² × 8 = SWL
1.5² × 8 = 18 ton
106
Calculate the sling tension for a three-leg bridle hitch that has twelve-foot-long slings, a vertical distance of 7.5 feet, and is lifting a load of 15 200 lb.
Sling tension = (W/N) × (L/V)
ST = (15 200/2) × (12/7.5)
ST = 12 160 lbs
107
What is the weight of a bronze shaft with a diameter of 0.5 feet and a length of 1.3 feet?
Density of bronze = 548 lbs/ft³
Volume = (πD²/4) × L
V = [π(0.5²)/4] × 1.3
V = 0.255 ft³
Weight = Volume × Density = 0.255 × 548
Weight = 140 lbs
108
What should the minimum overlap for an extension ladder be?
It should be one meter unless the manufacturer specifies the overlap.
109
What do the different duty ratings of Type 1A, Type 1, Type 2, and Type 3 for ladders correspond to?
Type 1A - Extra heavy-duty - Industrial construction
Type 1 - Heavy duty - Building maintenance
Type 2 - Medium duty - Light commercial
Type 3 - Light duty - Household use
110
How many times the load that may be imposed upon it must a scaffold be able to support?
At least four times the load.
111
How often in the horizontal and vertical directions must a scaffold be anchored by tiebacks or guy wires?
At intervals of 4.6 m vertical and 6.4 m horizontal.
112
How often must scaffolds be inspected?
Daily.
113
At what height must a temporary work platform have guardrails?
3.0 meters or higher above the ground.
114
How many times its base is a free-standing or rolling scaffold allowed to stand?
Three times the smallest dimension of its base.
115
Can firmly attached outriggers be used to achieve the 3 to 1 height to base ration that scaffolds require?
Yes.
116
How often must rigging be inspected?
At the beginning of each work shift.
117
What standard must a full body harness meet if manufactured on or after July 1, 2009?
CSA.
118
How often must you inspect your fall arrest equipment?
Before use on each shift.
119
What is recommended when attaching the hook to an eye-bolt?
Always use a shackle when attaching the hook to the load.
120
What is the safe and proper procedure if during a hoist the load tilts more than 5-degrees?
Lower the lift and rearrange the rigging.
121
How much force must exerted to lift a 1000 kg load when using a block and tackle with a 6:1 mechanical advantage?
167 kg.
122
How does a chain fall operate?
The operating chain turns the drive pulley and is one continuous loop called an endless hand chain. The drive pulley is connected to the lifting chain by a series of reduction or worm gears that multiply the amount of force the operator exerts on the hand chain.
123
How does a come-along work?
Chain-style come-alongs (ratchet lever hoists) have a ratchet lever instead of a running chain to activate a worm wheel to create mechanical advantage.
124
What type of built in overload protection do Trifor jacks have?
All Tirfor jacks are built with overload protection, which consists of a handle
shear pin that breaks when the load weight has been exceeded, preventing further movement of
the load.
125
What type of mobile support structure is in the image?
A gantry crane.
126
If a trolley tire, wheel, or axle fails, how far do drop stops limit the amount of fall to?
1-inch (25 mm).
127
What should be done if the width of the shackle’s opening is considerably greater than the thickness of the hook?
Packing washers should be used to center the hook on the shackle.
128
What are grab hooks designed to do?
To grab chain links.
Grab hooks have a narrow throat with a saddle equal in size to the throat opening, which creates a slot. Grab hooks are designed to grab onto chain links by sliding one link through the hook slot, with the throat opening at an upward angle and the basket at the bottom.
129
What hand signal is shown in the image?
Raise load or hoist up.
130
What hand signal is shown in the image?
Lower load or hoist down.
131
What hand signal is shown in the image?
Stop.
132
What hand signal is shown in the image?
Hoist slowly.
133
What hand signal is shown in the image?
Dog everything.
134
What hand signal is shown in the image?
Use main line.
135
What hand signal is shown in the image?
Use whip line.
136
What hand signal is shown in the image?
Alternate use whip line.
137
What hand signal is shown in the image?
Raise boom.
138
What hand signal is shown in the image?
Lower boom.
139
What hand signal is shown in the image?
Swing boom.
140
What hand signal is shown in the image?
Lower the boom and raise the load.
141
What hand signal is shown in the image?
Raise the boom and lower the load.
142
What hand signal is shown in the image?
Extend boom.
143
What hand signal is shown in the image?
Retract boom.
144
What hand signal is shown in the image?
Crane travel.
Make a pushing motion in the direction of travel.
145
What hand signal is shown in the image?
Crawler travel, both tracks.
Direction of travel is indicated by bicycle motion of hands.
146
What hand signal is shown in the image?
Travel one track.
Raised hand = lock track on that side.
Moving hand = move that track.
Indicate the direction of travel for the opposite track by making a circular motion with your other fist rotating vertically in front of your body.
147
The operator of such a hoist may not always be able to see the signaler, what is the system of sound signals or light signals that has been devised.
* “STOP”: one bell or flash
* “RAISE”: two bells or flashes
* “LOWER”: three bells or flashes
* “ALL CLEAR”: four bells or flashes
148
Identify the crane shown in the image.
Carrier-mounted lattice boom crane.
149
Identify the crane shown in the image.
Rough terrain crane.
150
Identify the crane shown in the image.
Carrier-mounted hydraulic boom crane.
151
Identify the crane shown in the image.
Crawler-mounted lattice boom crane.
152
Identify the crane shown in the image.
Crawler-mounted hydraulic boom crane.
153
Identify the crane shown in the image.
Stiff leg derrick.
154
For cranes, how large must the blocking be so that it supports the outrigger floats?
At least 3 times as big.
155
What is the minimum overlap for extension ladders?
* 1 m (39 in.) for ladders extending up to 11 m (36 ft.).
* 1.2 m (4 ft.) for ladders extending to between 11 m (36 ft.) and 15 m (48 ft.).
* 1.5 m (5 ft.) for ladders extending to between 15 m (48 ft.) and 22 m (72 ft.).
156
How long may extension ladders be?
* Grade 1 extension ladders with two sections may be up to 18 m (60 ft.) long.
* Grade 1 extension ladders with three sections may extend up to 22 m (72 ft.).
157
How far must the ladder extend past the level of the landing to which it provides access.
At least 1 m (3 ft.).
158
What is the proper slope and extension past the landing for a 4 m ladder?
If A is 4 m (13 ft.), then B should be approximately 1 m (3 ft.), and C should be approximately 1 m (3 ft.).
Angle is roughly 72-degrees.
159
For job-built straight ladders what grade must the lumber be?
No. 1 Grade and better.
160
For job-built straight ladders what size must the side rails be?
* Side rails (stiles) must be 38 × 89 mm (2 × 4 in.) for ladders up to 5 m (16 ft.) long.
* Side rails (stiles) must be 38 × 140 mm (2 × 6 in.) for ladders up to 7.3 m (24 ft.) long.
161
For job-built straight ladders what size must cleats or rungs be?
* Cleats or rungs must be 19 × 64 mm (1 × 3 in.) for ladders up to 5 m (16 ft.) long.
* Cleats or rungs must be 19 × 89 mm (1 × 4 in.) for ladders over 5 m (16 ft.) long.
162
For job-built straight ladders what must the distance between side rails be?
* The distance between side rails (stiles) must be between 380 mm (15 in.) and 500 mm
(20 in.).
163
For job-built straight ladders what must the distance between side rails be?
* Space the cleats at 300 mm (12 in.) centers.
164
How high do OHS regulations allow wooden scaffolds to be built?
Up to 15 m (50 ft.) high, but they are rarely used for work platforms above 6 m (20 ft.).
165
On scaffolds, at what height must guardrails be installed?
Above 3 m (10 ft.) from the surrounding grade.
166
For scaffolding, what size must the mudsill be?
* For long mud sills, use lumber no smaller
than 38 × 235 mm (2 × 10 in.).
* If a mud sill is placed under a single leg, it should be built from plywood with dimensions of 38 × 300 × 300 mm (1 1/2 × 12 × 12 in.).
167
What size must platforms be?
* Manufactured planks must be a minimum width of 20-inches.
* Lumber planks must be fitted with cleats on the underside and must extend beyond the supports by at least 6-inches, but not more than 12-inches.
168
On scaffolding, when must guardrails and toe-boards be installed?
Whenever the work platform is 3 m (10 ft.) or more above the ground.
169
For rolling scaffolds, what degree of level must the floor be at?
3 degrees of level and free of depressions and
obstructions.
170
For rolling scaffolds, when must casters be fitted with locking devices or brakes?
When workers are on the scaffold more than 3 m (10 ft.) above floor level.
171
How high is a rolling scaffold allowed to be relative to its base?
The height of a rolling scaffold must not exceed three times the base dimension.
172
At what height of rolling scaffold is a worker on the rolling scaffold not allowed to move the scaffold.
If the height of the platform exceeds 1 ½ times the minimum base dimension.
173
What dimensions must toe-boards be?
* 100 mm (4 in.) in height above the work platform.
* No more than 13 mm (1/2 in.) clearance between their low edges and the work platform.
174
What is the maximum allowed slope of the floor when using a rolling scaffold?
Within 3-degrees of level.
175
What is the maximum spacing allowed for the supports of scaffold planks if the scaffold is to
be used by a bricklayer?
2100 mm (7 ft.).
176
What is the minimum width allowed for a work platform?
2 plank widths.
177
What is the maximum allowed height for a rolling scaffold that is being moved by workers other than those on the scaffold?
2 times its minimum base dimension.
