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Hello!
My name is Yee Pin and for the next thirty minutes, I am going to touch on the working
at height aspects of design for safety from the perspective of an end-user.
Now, why from the end-user's point of view?
Because I am sure that we all agree that we need to design with the end-user in mind.
For the simple fact that the end-users are the ones that designers are trying to protect.
In this case, from getting killed from falling from heights. And I have been an end-user
for almost ten years in the field of work at height.
To start off, let's take a quick look at responsibilities of designers as stated in the Workplace Safety
and Health Council's (WSHC) “Guidelines on Design for Safety in Buildings and Structures”.
Designers are expected to consider “how buildings or structures can be constructed,
cleaned, maintained, and de-commissioned or demolished safely” in their design.
For this presentation, due to time constraint, let's focus only on some of the expectations
for maintenance and cleaning:
designing safe permanent access; and
specifically to the roof;
safe temporary access to allow for painting and maintenance of facades
In the GUIDE process outlined in the WSHC guidelines, the second phase of the design
review studies the risks related to the maintenance and repair of the building.
Again, due to limited time, we will only look at some design considerations for edge protection
and anchor points.
And now, we can establish the basis of the sharing.
We are going to assume that working at height is required, that is, elimination or substitution
of Working at height in the Hierarchy of Control Measures, has been evaluated by designers
and deemed unavoidable. And working at height in the context of cleaning and maintenance
activities.
There will be a heavy emphasis on fall protection and prevention systems, because that's what
end users mostly use when they have no alternative means but to work at height.
And, by approaching this topic from the perspective of an end-user, I hope that at the end of
the session, we can bring back some design considerations not normally found in textbooks.
Buildings are getting more prestigious in appearance and are often highly adventurous
in their architectural form. But all roofing systems require:
Cleaning: Periodic Removal of leaves and debris from entire roof, gutters, rooflights etc.
Inspection: Upstands, flashings, Rooflights, smoke extractors
Maintenance: Essential requirement to uphold warranties, ventilation fans, lifts, antennas
Repair: Glass replacement, cladding panels, post-storm
In this case study of a real-life job, we were required to replace cladding panels on
a sloped roof and line the roof gutter with waterproof membrane.
Please pardon the rudimentary sketch.
The roof slopes downwards towards the apex here. The gutter is indicated by this dotted
line.
Access is by this hatch here.
When we did the initial site visit for our risk assessment and to plan the work procedures,
we were very glad to see that there were permanent anchor posts provided for temporary lifelines.
Ten years ago, when I first started in fall protection and working at height, we would
be lucky to find something solid enough to secure our lifelines. So there is design for
safety considered. But is it sufficient to protect end-users?
The challenge we faced then, on this job was actually safe access.
How are we going to move upwards on the inclined roof from the roof hatch, point X here
to point A, almost 10 metres away safely?
Remember, the anchors are permanent, but the lifelines are not. We have to set it up ourselves
and in the meantime, we are totally exposed to slipping off the roof and falling “splat”
on the ground 20 floors below.
And also, moving from point A to B to C and so on, how can we be protected from falling
to our deaths over the lip of the roof here.
Normally, we can use twin lanyards to move from point to point safely, as shown in this
diagram.
We hook on one anchor, unhook from another and hook on to the next, always remaining
attached to at least one anchor point while moving from point to point.
However, in this case study, the anchor posts were located too far apart for this very widely
used method.
We found out that they were designed and positioned as such for rope access or vertical lifelines
in mind, to provide maximum coverage over the roof surface, which is good.
Less anchor posts, less cost.
However, as an end-user, I would also like to have some safety provisions while setting
up these temporary lifelines and not to forget, when dismantling them after the job is completed.
Next, let's look at the roof hatch.
This is the actual photo of the roof hatch and you can see one anchor post down by the
corner.
Looking down into the roof hatch in the next photo, you can see that the way up to this
roof hatch is by climbing through the space frames.
It was hard work to move through the space frames using the twin lanyard method for our
safety and to manoeuvre our equipment through it. Imagine trying to pass cladding panels
through this maze and through the roof hatch!
More can be done to design and provide for safe access to the roof for end-users and
their tools and equipment.
In fact, although I have personally not seen it here in Singapore yet, having guardrails
and self-closing gate at the roof hatch can protect end-users from falling through it,
especially when they are standing there passing tools, equipment and material through.
All it takes is a missed step to fall through the hatch and injure themselves... like in
this video.
For those who have seen this video before, just bear with me for a while.
So what do you think happened to this lady?
Case Study 2. Here we have another roof surface. Unlike the previous case study, we have an
anchorage bar running along the top of the roof for fall protection and rope access.
From the end-users perspective, anchorage bars are more “convenient”.
Unlike anchor points, they provide for continuous anchorage.
I can hook up and slide along the anchorage bar to move. This means relatively less hooking
and unhooking my lanyard or lifeline.
Less hassle also means more likely that it will be used. And, we will not have the issue
with anchor posts being too far apart as in the previous case study.
This is good for us.
However, often we are unsure of how many persons we can put on the anchorage bar safely.
Unlike an EN795 certified eye bolt which we know is usually for one person, with anchorage
bars, it is hard for us to tell.
Signages are supposed to be displayed indicating the number of persons allowed (just like for
scaffolding), inspection date and next maintenance / inspection (we will talk about provisions
for maintenance and inspections later).
This applies to permanent lifelines as well as anchor eye-bolts as shown in the pictures.
These information will help the end-users in planning their safe work procedures and
will be greatly appreciated.
Next, how are we going to access to the rooftop?
There is no roof hatch and access was supposed to be from inside the louvres, out through
an access door here.
Then using the anchor posts along the side here, to climb up onto the roof.
Hard work, but not do-able?
Sorry! Hard work, not an ideal access but do-able.
The challenge was, how were we going to get up to the access door at the louvres? Based
on the drawings, there were supposed to be ladders but when we were there, they were
not installed.
OK, a quick recap of the previous two case studies.
First, there is a difference between designing for safe access and designing for the work
at height activity itself.
Second, the design needs to accommodate the tools, equipment required for the anticipated
cleaning and maintenance tasks, to allow the end-users to access and egress safely with
them.
Also, the fall protection equipment used by the end-users needs to be considered, for
example, are they using a 1-metre lanyard or a 2-metre lanyard?
Third, the fall protection systems, number of anchor points provided should be sufficient
for the number of end-users required to complete their tasks within the given time frame.
For example, if the owner requires that the external facade cleaning is to be completed
within 3 weeks, then the design needs to cater for the number of end-users required to do
so.
Or else the job cannot be completed on time and the owner will not be happy.
And put up a sign to inform end-users so that we do not unknowingly overload the system.
A horizontal lifeline serves as an extended, long anchorage for one or more users with
personal fall arrest systems. It is increasingly becoming more common in Singapore so we are
going to spend some time on this.
Once the system is installed, end-users are at the mercy of the design.
There are certain inherent risks in its configuration and placement and end-users can only do very
little to mitigate them.
In this example, access to the roof of the main building is by the roof hatch here.
The Horizontal Lifeline 1 is positioned as such to provide safe access along the edge.
What is the potential hazard here should the end-user falls along this section here?
With the deflection of the lifeline, the end-user might hit the roof of the adjacent annex,
as shown in this diagram.
If the end-user falls here, then there is sufficient clearance height for him to fall
and not hit against another surface. So we only have to worry about rescuing the end-user
after the fall.
Next, on the annex rooftop, access is by the door here,
near the roof edge,
and we have a few configurations for discussion.
Horizontal Lifeline 2 is positioned on the wall.
For the end-user to reach to the roof edges here, a long lifeline is necessary.
If he falls here, then he will “swing back” and hit against the wall or even the ground
if the annex is not high enough.
Horizontal Lifeline 3 is configured as a straight line and is positioned in the middle of the
roof.
Similarly, for an end-user to reach this corner here, a long lifeline is necessary and should
he fall, there is a potential hazard of swing-back or swing-down.
Horizontal Lifeline 4 will probably cost more than the other two. It runs along the perimeter
of the roof and provides for an end-user to hook on once he enters through the door.
For this configuration and positioning, using a 2-metre lanyard is sufficient and minimizes
the swing-back and swing-down in a fall.
So it is not so simple as just putting a horizontal lifeline there.
A risk assessment should be conducted taking into consideration the surrounding structures
and clearance height required, to determine the safest configuration and positioning.
Some considerations when deciding to use horizontal lifelines.
The clearance height required. In the previous example, a fall on Horizontal Lifeline 1 may
result in the end-user hitting the adjacent roof.
Designers may want to consider using a rigid horizontal lifeline with less deflection to
mitigate this or to reduce the span by increasing the number of intermediate anchors.
The Maximum Arrest Force or MAF on the end-user and its implication on the strength requirements
of the system components, anchorages and supporting structure has to be understood.
A balance has to be struck between minimizing the Maximum Arrest Force and reducing clearance
height. To reduce the Maximum Arrest Force and hence minimize the damage to the roof,
may mean increasing the deflection to absorb the energy.
But this will lead to higher clearance height required to fall safely and a higher risk
of the end-user hitting against an object.
So what kind of forces are we talking about? In a very simplistic view for illustration
purposes: an EN355 energy absorber is designed to reduce the maximum arrest force to a 100kg
end-user to a maximum of 6 kilonewton in a fall.
Assuming a flexible horizontal lifeline with a 10-metre span deflects by this much as shown
in the diagram; resolving the vectors will already give more than 11kN force at the end
terminations.
Again, I stress that this is not the correct calculation method for horizontal lifelines.
It is actually much more complicated and the impact forces generated may be even higher.
It is simplified so that we can understand is that a person falling can generate an impact
load many times his weight.
In several Canadian and American jurisdictions, a Professional Engineer is required to approve
designs and installations of horizontal lifelines.
Pre-engineered horizontal lifelines including their performance, design, testing and labelling,
are covered by Canadian Standards Association's Z259.13-04 “Flexible Horizontal Lifeline
Systems” standards.
Custom designed, on-site built horizontal lifelines are covered by
Z259.16-04 “Design of active fall protection systems”.
This is the formula for Maximum Arrest Force. You can use this to calculate the the Maximum
Arrest Force to the end-user when he is falling on a vertical lifeline or lanyard.
But, again, I stress, this is not for horizontal lifelines systems.
To get a visual on the Maximum Arrest Force that we need consider, I'm going to show a
short video clip.
In this demonstration, we dropped a two hundred and twenty pound mannequin only six feet.
When the Mannequin hits the bottom of its six-foot drop, you can see the violent forces
at work.
Now, look at the difference when you incorporate a shock absorbing lanyard.
The force on your body has dropped from almost five thousand pounds to less than nine hundred.
That is why the European and American standards requires the anchorage strengths as stated
in this table.
The European standards require the fall arrest anchor for each individual to be able to hold
10 kilonewtons for three min, the American standards require it to be 22 kilonewtons.
That said, it is our experience that engineers often underestimate the impact loads generated
in a fall, and hence, the strength required of anchors in fall arrest systems.
It is not unusual to see engineers applying a safety factor of two for a static load of
a hundred kilogram user, without considering the dynamic amplification in a fall.
This works out to about two kilonewtons. This is grossly below the strength of anchors required
by European and American standards, as stated in this table.
A poorly engineered anchor that fails in a fall can have two consequences:
It jeopardises the safety of users depending on it, and it may also damage the integrity
Also, since rope access, also known as abseiling, spider-man etc. is also becoming more widely
used, we should also take note that the code of practice for rope access requires anchorage
strength of fifteen kilonewtons, higher than that for fall arrest anchors.
Case Study 3.
Covered walkways are a common sight in Singapore and they have to be cleaned regularly of algae
and debris.
In this photo, the end-users are “wet” cleaning the canopy. The surface is wet and
slippery, which increases the probability of them slipping and falling but they have
nothing to hook on to and are not protected from falling.
Yes, on their end, they may be able to do the job using a Mobile Elevated Work Platform
such as a scissors lift but on the design side, what can be provided for them?
One suggestion can be to retrofit a horizontal lifeline as indicated by the red line in the
photo.
Whether it should be a flexible or rigid one has to be an outcome from evaluating the clearance
height and MAF on the worker. But most importantly, can the structure support the load?
Another quick recap before we move on to the last part.
When designing for fall protection systems, architects and consultants need to cater for
the dynamic impact forces on structures and anchors, which can be many times the weight
of the end-users.
And design the supporting structures to be sufficiently strong for retro-fitting fall
protection systems.
Sometimes, it is only later that we discover that certain areas require fall protection
and it is so much easier if there are supporting structures strong enough as anchors for end-users
to set up temporary fall protection or for installers to retro-fit permanent solutions.
We will cover provisions for rescue and replacement, and translating design into reality shortly.
As a result of technological advances in fall protection, effective mitigation of fall hazards
no longer is such a far-fetched goal.
Fall arrest systems can be fixed to all major composite, built-up-on-site, standing-seam,
secret-fix and membrane roofing. Depending on the nature of the roofing system, posts
can be fixed by means of stitching screws, split clamps, rivets, toggle bolts or mechanical
anchors. These photos show some examples.
There is no need to fix through the roof or attach to structural steel or purlins. Importantly,
this top-fixing process ensures that the function of the building is not compromised during
installation.
In this photo, you can see this gutter that needs to be inspected and maintained.
Fall protection was provided by installing foldable guardrails onto the kalzip roofing
sheets using the S5 adapter from Kalzip.
When the end-user needs access to the gutter, they push it up and they are protected from
falling off the edge. When they are done, they fold it down and the architect is happy
that the guardrails cannot be seen from below.
So a variety of anchorage solutions can be utilized by the end-user, provided that the
supporting structure is sufficiently strong to take load.
Another example is the 318-metre Aspire Tower in Doha. I was there as a consultant to help
out with the work method for external cleaning.
There, almost everything is covered in a perpetual layer of sand. And the owner wanted the tower
cleaned as often as possible so that guests can look out the window and enjoy a nice view
instead of a layer of sand.
So how many cleaners do you think is required to clean this building and how to do it safely?
In their design, they incorporated ladder access and horizontal lifelines.
In this photo, you can see right at the top, they have this ladder that moves horizontally
along this track around the structure.
So cleaners can move vertically up and down the ladder as well as horizontally across
by rolling the ladder along the track.
Fall protection was provided by incorporating a safety rail into the ladder stile
where cleaners can attach their fall arrester device.
This concept is deployed along the height of the tower.
For example, to clean 10th to 12th floor,
there is a catwalk running around perimeter at 10th floor to provide access to the ladder
which is from 10th to 12th floor.
Fall protection while walking on the catwalk is by means of a horizontal lifeline around
the whole perimeter.
By having several rings or bands of catwalks and access ladders around the tower,
multiple crews can be deployed simultaneously for faster cleaning.
At the same time, the end-user is protected while moving horizontally and vertically.
New buildings and structures are better designed for safety but there are still a lot of existing
ones around.
End-users cleaning and maintaining these existing buildings and structures are exposed to falling
hazards as seen in these photos.
Even for those setting up the “safe access” such as the suspended scaffold erectors in
the middle photo, they are not protected.
Can there be an anchor point installed for them so that they can attach a lanyard?
And can this same anchor point
also be used to anchor the independent lifelines
for the suspended scaffold users?
I leave it to you as a little exercise to think about.
Window Washer: I am about to splatter all over the concrete and they are going to call
it an accident.
Window Washer: Dave! Help me out! Dave: Hang on man!
Window Washer: But the outrigger beams weren't pinned together!
Window Washer: Hurry! Dave: Just hang on!
Window Washer: This is the first time that I didn't tie off properly...
Dave: Oh man! It's a good thing I had you clipped in.
So the lesson learnt: an independent lifeline is life-saving. But what's next after the
fall?
This is a newspaper clipping for 18 Aug 2009 in Brooklyn where a worker fell 4 stories
to his death when the scaffold collapsed.
Two workers were left dangling.
Workplace Safety and Health Act Section 12 clause (3)(d) requires employers to develop
procedures for emergencies.
The code of practice on working safely at height also requires a written height rescue
plan. So legally, and morally, we need to plan for what happens should a person falls
and is hanging in mid-air like in this photo.
One key consideration in planning a height rescue, is ensuring the safety of the rescuer.
A height rescue is not as simple as it seems, and it is always, always dangerous.
One of the greatest challenge is finding an anchor point for the rescuer and the rescue
kit. More can be done in the design for rescue operations.
Lastly, in order for the safe design to be effective, its intended usage must be communicated.
Personally, I think there is a breakdown in communication between the design team, builder
and the facility management when handing over.
Often, when contracted for jobs, the facility management are unable to advise us, the end-users,
on the safety provisions for work at height.
No doubt, we are obligated to develop the safe work procedures but we need to know the
breaking strength of the anchors, the capacity of the system, the safe way to access to the
roof, the fall protection equipment intended for, etc., etc.
These are critical information for end-users in their risk assessment
and to plan their work.
Just like you have maintenance manuals for your vehicles, televisions, etc, building
maintenance manuals with instructions on the safe access will be very useful for end-users.
In conclusion, wear the shoes of the end-user when reviewing building designs. Solicit input
from subject matter experts, including the end-users themselves and communicate it to
the end-users.
Our ultimate aim is to reduce risks at source for the end-users.
Thank you.