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Mettrology

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Metrology Laboratory
MECN3003 - Aeronautical Laboratory
Deepa Daya
Student number: 473706
Supervisor: Mr. R. Paton

A project report submitted to the Faculty of Engineering and the Built Environment,
University of the Witwatersrand, Johannesburg, in partial fulfilment of the requirements for the degree of Bachelor of Science in Engineering.

Johannesburg, March 2014

University of the Witwatersrand, Johannesburg
School of Mechanical, Industrial & Aeronautical Engineering

INDIVIDUAL DECLARATION WITH TASK SUBMITTED FOR ASSESSMENT

I, the undersigned, am registered for the course MECN3003 - Aeronautical Laboratory in the year 2014. I herewith submit the following task ”Metrology Laboratory” in partial fulfilment of the requirements of the above course.
I hereby declare the following:
• I am aware that plagiarism (the use of someone else’s work without their permission and / or without acknowledging the original source) is wrong;
• I confirm that the work submitted herewith for assessment in the above course is my own unaided work except where I have explicitly stated otherwise;
• This task has not been submitted before. either individually or jointly, for any course requirement, examination or degree at this or any other tertiary educational institution;
• I has followed the required conventions in referencing the thoughts and ideas of others;
• I understand that the University of the Witwatersrand may take disciplinary action against me if it can be shown that this task is not my own unaided work or that
I my failed to acknowledge the sources of the ideas or words in my writing in this task.

Signed this 13th day of March 2014

Deepa Daya

473706

i

Contents

Declaration

i

Contents

ii

List of Figures

iv

List of Tables

v

1 Background

1

2 Motivation

1

3 Literature Survey

1

3.1

Tolerances, Limits and Fits . . . . . . . . . . . . . . . . . . . . . . . . . . . .

1

3.2

Vernier Calliper . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

1

3.3

Micrometer Screw Gauges . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

1

3.4

Sine Bar and Slip Gauges . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

2

3.5

’Go, No Go’Gauges . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

2

3.6

Ovality . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

2

3.7

End-Face Runout . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

2

4 Objectives

2

5 Apparatus, Procedure and Precautions

3

ii

5.1

Apparatus . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

3

5.1.2

Procedure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

3

5.1.3

Precautions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

3

Exercise 2: . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

4

5.2.1

Apparatus . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

4

5.2.2

Procedure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

4

Exercise 3: . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

4

5.3.1

Apparatus . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

4

5.3.2

Procedure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

4

5.3.3

5.3

3

5.1.1

5.2

Exercise 1: . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Precautions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

4

6 Obseravtions, Data Processing and Results

5

7 Discussion

5

8 Conclusions

6

A Appendix title

8

B Appendix B

11

iii

List of Figures

A.1 Vernier Calliper . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

8

A.2 Micrometer Screw Gauge . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

8

A.3 Sine Bar and Slip Gauge Layout . . . . . . . . . . . . . . . . . . . . . . . . .

9

A.4 ’Go’,’No Go’ Gauge

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

9

A.5 Shaft Assembly . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

10

iv

List of Tables

v

Abstract
The science of metrology was demonstrated in the laboratory using several test pieces and measuring instruments such as the vernier calliper, micrometer screw gauge, ’Go,No Go’ gauge and the sine bar. The objective was to develop an understanding in precision measuring methods that may be encountered in the engineering sector
It was found that each instrument used, provides a different accuracy, which is suitable for different applications.The results displayed the presence of ovality and end surface run out on the test pieces.The ’Go,No Go’ gauge measures if an manufactured component is within the suitable tolerances. The sine bar accurately measures the angle of a given component.

vi

1

Background

Metrology is known as the science of measurement conducted through experimental and theoretical practises to determine the uncertainty of measurement[1]. Metrology can be broken up into 3 distinct sectors, namely, scientific, engineering and industrial metrology.
Scientific metrology is concerned with the standardisation and development of unit systems.Engineering and Industrial metrology are applied branches of metrology. Engineering metrology has to do with precise value measurement, whereas industrial metrology is the application of qualitative measurement in industry[2].

2

Motivation

In the manufacturing industry components need to be manufactured accurately according to design specifications.It is extremely difficult to have minimal errors.Through the metrology methods used, the errors can be minimised, thus improving the accuracy of manufacturing processes. 3
3.1

Literature Survey
Tolerances, Limits and Fits

A tolerance is usually included when machine parts are designed. The tolerance describes how accurately the part should be machined (i.e. A small tolerance is required for a part that requires high precision). The application of the part should be considered when determining the tolerance.

3.2

Vernier Calliper

Vernier callipers are short scales that slide on a longer scale. The longer scale indicates the subdivisions.Verniers callipers can be used to measure internal,external and depth measure1 ment. It provides a measurement with the accuracy of 100 th of a millimetre[3]. See Figure
A.1 in Appendix A

3.3

Micrometer Screw Gauges

Micrometers are able to measure more accurately than a vernier calliper, they have an accu1 racy of 1000 th of a millimetre.To measure an object, the object is placed between the anvil and spindle, the object is then secured by rotating the thimble using the ratchet, then simply read the measurement off the scale[3].See Figure A.2 in Appendix A

1

3.4

Sine Bar and Slip Gauges

A sine bar is an instrument with its fixed length accurately ground to a specific dimension[4].Its purpose is to set surfaces to the desired angle, with the use of slip gauges. Slip gauges are high-carbon steel blocks that have been hardened, heat treated and lapped to produce a high degree of accuracy[5]. The tolerance of these blocks are so high that if they are placed together for a period of time, they will permanently attach to each other due to an atomic bond formed. The height of the slip gauge is calculated as follows:
HeightSlipGauge = LengthBar × sin(angleElevation )

(3.1)

See Figure A.3 in Appendix A

3.5

’Go, No Go’Gauges

A ’Go, No Go’ gauge is used to measure whether a machined part is within the required tolerances. The instrument has 2 ends, one end is set to the exact value required (i.e. ’Go’), the other side is the upper tolerance limit (i.e. ’No Go’). If the ’No Go’ side is not satisfied and the ’Go’ side is satisfied the the hole is the correct size. If both conditions are not satisfied the hole will need to be re-machined, and if the ’No Go’ side is satisfied the hole is to big[6].See Figure A.4 in Appendix A

3.6

Ovality

Ovality is the measure of the ’out of roundness’ of an object, in other words the deviation of a circular bar from a perfect circle[7].

3.7

End-Face Runout

End-face runout is the measure of flatness and eccentricity of a shaft end.

4

Objectives
• Develop an understanding and proficiency in precision measuring methods that may be encountered in the engineering sector
• Gain experience with measuring instruments such as vernier callipers, micrometer screw gauges and sine bar
• Using the vernier calliper determine the ovality of the shaft assembly
• Using the dial gauge determine the end-face runout (i.e. Surface quality)of the shaft assembly 2

• Compare the accuracy between different measuring instruments
• Using the Go, No Go gauge, assess the tolerances of various samples
• Determine the dimensional accuracy of a manufactured component
• Determine the accuracy of the angle of a manufactured component

5

Apparatus, Procedure and Precautions

5.1

Exercise 1:

5.1.1

Apparatus

• Vernier Calliper (0.02mm of accuracy)
• Micrometer Screw Gauge (0.001mm of accuracy)
• Snap Gauge
• Dial Gauge
• Shaft Assembly (see Figure A.5 in Appendix A)

5.1.2

Procedure

1. In order to calculate the ovality of a shaft assembly, measure the external diameter of the assembly at 3 different locations (i.e. Top, Middle and Bottom).
2. Rotate the shaft assembly 90 ◦ and repeat step 1, the difference in measurement gives rise to the ovality
3. The end-face runout is measured by clamping the test sample using the inline centre.
This clamps the 2 ends of the part through the centres. A dial gauge was pressed on to the face of the sample. Then rotate the shaft assembly and the deflection is measured on the dial gauge.
4. Measure the total length of the shaft assembly using a vernier calliper
5. Measure the length of Shaft 1 (See Figure in Appendix 1) using a vernier calliper
6. Measure the diameter of Shaft 2 (See Figure in Appendix 1)

5.1.3

Precautions

• Ensure that measurements of the shaft diameter are taken through the centre of the shaft when using the micrometer
• Calibrate all instruments before performing the experiment and ensure they are on zero
• Take note of what the divisions on the dial gauge signify

3

5.2

Exercise 2:

5.2.1

Apparatus

• ’Go, No Go’ gauges
• 3 test sample bushes

5.2.2

Procedure

1. Insert the ’Go’ side into bush 1, state whether it fits or not
2. Insert the ’No Go’ side into bush 1, state whether it fits or not
3. Repeat step 1 and 2 for test sample 2 and 3

5.3

Exercise 3:

5.3.1

Apparatus

• Sine bar
• Slip gauge blocks

5.3.2

Procedure

1. Calculate the perpendicular height needed for the specified angle using basic trigonometry 2. Choose slip gauges such that the sum of the their height is equal to the value in step 1
3. Place slip gauges in correct position
4. Place test sample on to the sine bar
5. Run the dial gauge over the surface of the test sample
6. Record the value on the dial gauge

5.3.3

Precautions

• Ensure that the slip gauges are clean before use (Note the slip gauges are delicate and need to be handled with care)
• Environment should be kept at constant temperature to ensure thermal expansion is minimised • Wring slip gauges carefully to remove air between them

4

• Minimal slip gauges should be used to minimise errors
• Do not leave slip gauges stacked up for too long as they will bond together

6

Obseravtions, Data Processing and Results
Diameter 1[mm]
Diameter 1 [mm]
Ovality
Diameter 2 [mm]
Length of Shaft 1 [mm]
Length of Shaft 2 [mm]
Total Length [mm]
End-face Runout [µm]

Measurement 1
39.980
39.978
0.002
74.98
65.092
34.97
100.4
9 divisions ×2µm = 18
Bush
1
2
3

Go
Fail
Pass
Pass

Measurement 2
39.980
39.980
0
74.97

Measurement 3
39.998
40.000
0.002

No Go
Fail
Fail
Pass

Exercise 3: Height calculated 57.657mm.Four slip gauge sizes were used to make up this height (1.007mm, 1.15mm, 5.50 mm and 50mm).Deviation of the angle was found to be
0 ◦ 0’0.5”

7

Discussion

In the first experiment, the diameter of the shaft was measured at 3 different locations using a vernier calliper.Measurements were then taken again at the same locations but in a perpendicular direction. The original diameter of the shaft was assumed to be 40mm, but all measurements taken varied. The measured values taken along the shaft were all less that
40mm. This most likely indicates wear on the shaft due to handling. The presence of ovality can be observed by the differences in measurements at each point. The differences stay between tolerance. The end-face runout of the shaft was measured at 18µm. This value changes as the circumference of the test are changes (i.e. the distance from centre changes). This value is an acceptable value and can be attributed to either wear and tear or variations in the manufacturing process.The length of the shaft 1 should be determined using the vernier calliper shoulder as this is the most accurate.
In the second experiment,it was observed that bush 2 was the ideal size, since it satisfied both conditions of the ’Go, No Go’ gauge were satisfied. Bush 1 was observed to be under-sized. This can be rectified by further machining the bush to the correct dimensions.
Bush 3 was observed to be oversized. This could be rectified by enlarging the hole further and then re-sleeved with a cylindrical piece of metal. Bush 3 would be saved depending on the forces meant to be subject to the bush, else it would be scrapped.

5

In the third experiment, a sine bar was used to confirm the angle of a test specimen. One of the precautions were to use the fewest possible slip gauges to minimise the error as the spaces between slip gauges would yield a fraction of an error. The angle of the specimen was found to be 27.007639 degrees. The component is therefore within tolerance as the given dimension is 27 ◦ ± 0.5 ◦ . Errors could be attributed to the fact that the slip gauges were not wrung properly.

8

Conclusions
• The accuracy of the measurements are determined by the measuring instrument used, as they each have different resolutions and accuracies.
• An understanding of accuracies and tolerances was developed. It was also noted that manufacturing and machining processes are not perfect. Uncertainties and inaccuracy will always be present.
• Ovality, end-face runout and length of the shaft were all within acceptable tolerances.
Discrepancies can be attributed to wear and tear as well as inaccuracies during manufacturing
• Bush 1 and 3 failed.These must be re-machined to achieve desired outcome
• Sine bar and slip gauges can be used to measure the accuracy of an angle. Errors can be attributed to slip gauges not being wrung properly. Angle measured was within tolerance. 6

References
[1] Metrology - Definition and More from the Free Merriam-Webster Dictionary. [ONLINE] Available at: http://www.merriam-webster.com/dictionary/metrology. [Accessed
12 March 2014].
[2] Types of metrology — UNBS. 2014. Types of metrology — UNBS. [ONLINE] Available at: http://www.unbs.go.ug/index.php/metrology-1/types-of-metrology. [Accessed
12 March 2014].

[3] 2014. . [ONLINE] Available at: http://physics.sierracollege.edu/People/dcalabrese/P2A/Physics202
[Accessed 12 March 2014].

[4] 2014. . [ONLINE] Available at: http://mech.sggs.ac.in/sites/default/files/u9/MMM20Experiment20
[Accessed 13 March 2014].
[5] Elementary Knowledge of Metalworking. National Maritime Research Institute. [Online]
[Cited: 21 April 2009.]

[6] . 2014. . [ONLINE] Available at: http://www.aajansson.com/pdfs/understanding20fixed20limit20ga
[Accessed 13 March 2014].
[7] Ovality - Metal Fabricating Glossary. 2014. ovality - Metal Fabricating Glossary. [ONLINE] Available at: http://www.thefabricator.com/glossary/ovality. [Accessed 13 March
2014].

7

Appendix A

Figure A.1: Vernier Calliper

Figure A.2: Micrometer Screw Gauge

8

Figure A.3: Sine Bar and Slip Gauge Layout

Figure A.4: ’Go’,’No Go’ Gauge

9

Figure A.5: Shaft Assembly

10

Appendix B Appendix B

11

Laboratory Risk Assessment Checklist
Campus: University of Witwatersrand

Faculty/School/Unit Engineering

Laboratory Type: Closed Engineering Laboratory
Assessment Date: 12/03/2014
Assessors Name: D Daya

Assessors Signature:

Approved by: Mr R. Paton

Signature:

Main Laboratory Functions: Climate Controlled Room for Evaluating the Accuracy of Miscellaneous
Metrological Apparatus.

Part 1 - Hazard Identification

The table below will assist you in identifying hazards when completing the section entitled “These Hazard
Exist”

A Could people be injured or made sick by things such as:














Noise – No
Light - No
Radiation - No
Toxicity – No
Infection - Yes
High or low temperatures - No
Electricity - Yes
Moving or falling objects (or people)
Flammable or explosive materials
Malenals under tension or pressure (compressed gas or liquid; springs) - No
Any other energy sources or stresses - No
Bio-hazardous material - No
Laser -No

B

What could go wrong?



What if equipment is misused?
Electrical Shock, Cuts and possible decapitation.

What might people do that they should not?
Put their digits in moving parts

How could someone be killed?
Severe Loss of blood

How could people be injured?
By cutting themselves, short circuiting electrical components.

What may make people ill?
Eating in the lab after touching equipment

Are there any special emergency procedures required?
Fire Exit.

12

C










Can workplace practices cause injury or sickness?

Are there heavy or awkward lifting jobs?
No
Can people work in a comfortable posture?
Yes
If the work is repetitive, can people take breaks?
Yes
Are people properly trained?
Yes
Do people follow correct work practices?
Yes
Are there adequate facilities for the work being performed? Yes
Are universal safety precautions for biohazards followed? Yes
Is there poor housekeeping? Look out for clutter, torn or slippery flooring, sharp objects sticking out, obstacles etc - No

E



Imagine that a child was to enter your work area
Of what, would you warn them to be extra careful?
Vernier Callipers
What would do to reduce the harm to them?
Safety Goggles

D

How might these injuries happen to people?



Broken bones
NO
Eye damage
YES
Hearing problems
NO
Strains or sprains
NO
Cuts or abrasions
YES
Bruises
YES
Burns
YES
Lung problems including inhalation injury/infection
NO
Skin contact
NO
Needle-stick injury
YES











F

What are the special hazards?



What occurs only occasionally - e.g. during maintenance and other irregular work?
Not in Particular

These hazards exist: (Please √)
Physical:
Noise

Chemical:
√ Liquids

Biological:
√ Human blood

Mechanical/Ergonomic:

Psycho-social:

√ Posture

√ Worry



√ Movement

√ Work pressure



√ Monotony



√ Unsocial hours



Shift work



and saliva
Vibration

√ Dusts

√ Insects

UV

Fumes

Mites

X-ray

Fibres

Moulds

Laser

Mists

Yeasts

Heat and cold

Vapours

Fungi

Electricity

√ Gases

Bacteria

Extremes of pressure √ Compressed
√ Acids

√ Illumination and visibility

Viruses

Heavy weights

Repetitive actions

Sharps



gases

Mercury

Animals:
Rats

13

Needles
Physical
activity, exertion Mice



Rabbits

Sheep brain
Pig heart
Toads

Major Equipment:
Autoclave

Fume hood

Major sports equipment Vacuum

Compressed air

Trolleys/mechanical aids Bio-safety cabinet Radioactive

Sharps

Minor Equipment:

Bunsen burner

Water bath

Vernier



Ruler

Microscope



Materials:

Mild steel columns √

Waste Generated:

Biological

Chemical

Carcinogenic

Waste disposed of by:

14

General waste



Freezing

Medical waste bin

Incineration

Flushing sink

Disinfection

Autoclaving

Fume hood and water Sharps bin

Glass bin

MSDS

Fire Extinguisher

To help me prepare for an emergency I may need:

First Aid training √

CPR training

Safety Signs

Evacuation procedures √

Spill kit



South African
Standards

Personal Protective
Equipment





Emergency contact numbers could be needed for (List extension numbers below)
Security First aiders Floor Warden Emergency phone numbers are posted where?

On notice board in laboratories and by all telephones (Yes/No)

Part 2 - How to Asses Risk – Explanatory Notes

Risk Score:

ASSESSMENT OF RISK
Score and
CONSEQUENCES:

Action

statement

How severely it hurts someone (if it happens)?

4
Insignificant

LIKELIHOOD
How likely is it to

(no injuries)

Minor (first aid treatment only; spillage contained at

Moderate
(medical
treatment; spillage contained but

Major
(extensive
injuries; loss of production) Catastrophic
(death; toxic release of chemicals) A: Acute

ACT NOW – Urgent do something about the risks immediately. Requires immediate

15

site)

happen?

attention.

with outside help) 3
Almost certain expected in most circumstances Likely – will probably occur in most circumstances

3

3

4

4

4

High

High

Acute

Acute

Acute

H: High
2

2

3

3

4

4

Moderate

High

High

Acute

Acute

1

2

3

4

4

Low

Moderate

High

Acute

Acute

1

1

2

3

4

Low

Low

Moderate

High

1

2

3

3

Low

Low

Moderate

High

Follow management instructions e.g. policy/guidelines. Acute

1

Senior management decision is required urgently. High

M:
Moderate
1

Possible – might occur at some time
Unlikely – could occur at some time

Rare - may occur, only in exceptional circumstances

1. To use the matrix, first find the CONSEQUENCES column that best describes the risk. Then follow the
LIKELIHOOD row to find the description that best suits the likelihood that the consequence will occur.
The risk level is given in the box where the row and column meet.
2. When considering the likelihood of injury or disease, the number of people exposed, the extent of the exposure to the hazard and the likelihood that exposure will result in harm, all to be taken into account. 3. The estimate of likelihood will also depend on the effectiveness of the control in place. It is important to indicate what assumptions are being made about the controls in place.

L: Low

OK for now. Record and review if any equipment/ people/ materials/ work processes or procedures change.

Note:

ACUTE or HIGH Risk must be reported to the School’s Senior Management (HOS and/or Dean) and require detailed treatment plans to reduce the risk, where possible, to
MODERATE or LOW.

Adapted from Standards Australia Risk Management AS/NZS 4360: 2004

Risk Control

Emphasis is on controlling hazard at source. For instance, for those risks that are assessed as “High”, steps should be taken immediately to minimise risk of injury. Use the “hierarchy of controls” as listed below to determine the type of control measures that should be implemented:

16

Order No.

Control

Example

Firstly

Eliminate

Disposing of unwanted chemicals and out-of-service hazardous equipment, prompt repair of damaged equipment.

Secondly

Substitute

Using water-based instead of a solvent-based paint, using chemicals of lower concentration.

Thirdly

Isolation

barricades around trenches, fume cupboards, bio-safety cabinets.

Fourthly

Engineering

Ensure proper machine guarding, ventilation and extraction systems Fifthly

Administrative

Appropriate training to all staff, provision of adequate warning signs Sixthly

Personal Protective
Equipment

Use of gloves, glasses, ear muffs, aprons, safety footwear, dust masks, etc.

Part 3 – Completion of Laboratory Risk Assessment

Now that you have identified the hazards and using the information above, complete the following Risk
Assessment Form. Once the risk assessment has been completed, copies should be provided to:

Copies:

1. Laboratory/Academic Supervisor or their Representative
2. Summary/ Report - Campus OHS Committee Chair (for tabling at next OHS Committee
Meeting)

3. Manager, Campus Operations
4. Head of School

17

RISK ASSESSMENT

RISK CONTROL

REVIEW

HAZARD
IDENTIFICATION
No.

What harm can happen to people or equipment?

Risk
Score*
(See Matrix)

List any control measures already implemented Describe what can be done reduce the harm?

Whom
Responsible

By when

(see Risk Controls )

Are the
Controls
Effective?

Date
Finalised

(See page 3 for list of possible hazards) 1

Noise

2

none

Ear plugs

Personal
Protective
EquipmentSelf Sustaining

ASAP

No, none implemented NA

2.

Vibration

2

Possible damping system integrated within the system Possible improvements on damping system

Engineer

ASAP

Somewhat
Effective

NA

17

RISK ASSESSMENT

RISK CONTROL

REVIEW

HAZARD
IDENTIFICATION
No.

What harm can happen to people or equipment?

Risk
Score*
(See Matrix)

List any control measures already implemented Describe what can be done reduce the harm?

Whom
Responsible

By when

(see Risk Controls )

Are the
Controls
Effective?

Date
Finalised

(See page 3 for list of possible hazards) 3

Testing Rig looks unstable 3

None

Possible reinforcement of structure

Engineer

ASAP

No

NA

Repetitive actions

1

none

Possibly data acquisition by the computer relevant to the lab report

Administrative

ASAP

No

NA

Cuts from the
Vernier Callipers and dial gauge needle 2

None

By wearing gloves

EquipmentSelf Sustaining

ASAP

Not really

NA

4

5

18

RISK ASSESSMENT

RISK CONTROL

REVIEW

HAZARD
IDENTIFICATION
No.

What harm can happen to people or equipment?

Risk
Score*
(See Matrix)

List any control measures already implemented Describe what can be done reduce the harm?

Whom
Responsible

By when

(see Risk Controls )

Are the
Controls
Effective?

Date
Finalised

(See page 3 for list of possible hazards) 6

Gauging of eyes with Vernier
Callipers

3

PPE

Ensure goggles are worn at all times

EquipmentSelf Sustaining

Already in Yes operation NA

7

Falling down stairs

3

Railing and yellow paint
(awareness)

Possibly reduce the steepness of the stairs

administrative

ASAP

NA

No

19

20

rlogy…...

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