5. Recognising Machinery Hazards
• People may be injured as a result of contact with
– Machine parts in situ
– Ejected machine parts (eg if they break or become loose)
– Ejected material (eg glass from breakages, fluid from leaks in
hydraulic systems, items falling into machine)
• Hazards arise when machine parts move or have potential to move
– Rotary motions
– Sliding or transverse motions
– Reciprocating motions, ie up-and-down or back-and-forth
6. Machinery Hazards
• Moving Parts:
– Abrasion
– Cutting
– Impact
– Stabbing/Puncture
– Shearing
– Crushing
– Entanglement and Drawing-in
• Exposed Electrical Conductors
(>50 V ac or >75 V dc)
• Hot Surfaces
• Hot Liquids or Steam
• Sharp Points/Edges
• Ejected Machine Parts or
Materials
– Breakages and Releases
• Stored Energy
– Gravity
– Pressure
7. Moving Parts: Abrasion/Cutting
Abrasion
• Caused by friction between moving
part and skin
– Risk increases with roughness of the
surface + speed of movement
– Even smooth parts can cause burns if
moving at high speed
– Risk may be increased if body part is
unable to move away from hazard (true
for many machinery hazards)
Cutting
• An extreme (and deeper) form of
abrasion
– Risk increases with sharpness/shape of
edge + speed of movement
8. Moving Parts: Impact and Stabbing
Impact
• Caused when body part struck (but
not penetrated) by moving part
– Risk increases with momentum of
moving part - may also be influenced
by the shape of the part
Stabbing/Puncture
• Caused when body part punctured
by moving part
– Risk increases with sharpness of part
+ momentum
9. Moving Parts: Crushing and Shearing
Crushing
• Caused when machine parts move towards each other
and body part is caught in between
– Sometimes occurs between moving part and fixed
structure (eg wall or barrier) or between moving part and
material being worked
– Risk increases with momentum of the moving parts but
may be influenced by their shapes
Shearing
• Caused when body part is caught between 2 machine
parts moving past one another
– Sometimes occurs between machine part and material
– Risk increases with sharpness of parts + momentum
10. Entanglement and Drawing-in
• Caused when body part becomes caught on/in
machine parts
• Can occur through catching…
…on solid rotating surface, eg spindles, shafts
• Risk greater if surface rough or has projections, eg
screws, bolts
…between gaps in rotating parts (eg fan blades)
…in ‘in-running nips’, ie
• between counter-rotating parts
• between rotating parts + tangentially moving parts
• between rotating parts + fixed parts
• Injury occur directly from entanglement or because
body part is drawn into danger zone
• Risk significantly increased for persons
– wearing loose clothing, gloves, neck-ties or jewellery
– with long hair, or those using rags, etc
13. Burn Threshold vs Contact Period for
Different Materials
• In ideal conditions, accidental
contact period can be 0.5s
– Recommend min. period = 1s
• Actual threshold depends on
– Thickness of skin at touching point
– Moisture of skin surface (sweating)
– Contamination of skin (eg grease)
– Touching force
• Burn Threshold ≠ Pain Threshold
Source: EN 563:1994 “Safety of Machinery – Temperatures of Touchable Surfaces – Ergonomics data to establish temperature
limit values for hot surfaces”
Bare Metal: 65°C
Glass/Ceramics: 80°C
14. Possible Control Measures for
Hot Surfaces
• Reduce surface temperature
• Apply coating
• Apply insulation
• Install barriers, guards, etc
• Provide PPE (gloves, overalls, etc)
• Establish safe systems of work
– Affix warning signs
– Instructions/SOPs
– Training
– Supervision
– etc
• Use some combination of the above
16. Zero Access
• Where possible, guards must prevent access to danger zones
• Consider:
– All intended uses and foreseeable conditions of use
• Loading and unloading materials
• Clearing jams
• Cleaning and line clearance
• Set up, adjustment and lubrication
– Foreseeable mistakes and misuse by operators, etc
• Reflex behaviour in case of malfunction
• Lack of concentration/care
• Taking “line of least resistance”
• In particular, consider:
– Reaching over, under or around guards
– Crawling below and climbing over guards
– Inserting fingers, hands, arms into openings
19. Zero Access – Reaching Through Slots,
Square or Round Openings
Source: EN294:1992 Safety Distances for Upper Limbs
Eg for slot 15mm by
80mm, hazard must
be >120mm away
20. Zero Access – Reaching Through With
Limitation of Movement (examples)
Source: EN294:1992 Safety Distances for Upper Limbs
21. Zero Access – Other Situations
Reaching Through Irregular Openings
• Determine smallest dimensions (round, square
and slot) into which irregular opening could be
inserted
• Select corresponding 3 safety distances
according to previous table
• Select shortest safety distance
Source: EN294:1992 Safety Distances for Upper Limbs
Reaching Upwards
• h > 2700 mm
22. Zero Access - Reaching Over
Protective Structures
Source: EN294:1992 Safety Distances for Upper Limbs
Hazard must be
>400mm away
24. But before we talk about safeguards…..
• Eliminates the hazard so avoids the need for safeguards
• More likely to remain effective – avoids many issues, eg
safeguard maintenance, reliance on safe behaviours, etc
• Examples
– Avoid crushing hazards by increasing gaps between machine parts
– Limit mass and/or velocity of moving parts
– Separate low voltage control systems from higher voltage power
systems
….can we apply inherently safe design principles?
26. Fixed Guards
• Securely held in place, ie
– Permanently (eg welded or riveted); or
– With fixings that require special tools not
held by operators
• Where possible
– Use retained fastenings
– Guards do not remain in place without
fastenings
28. Moveable Guards
• Moveable guards typically used if access
requirement > 1 time per shift
• Moveable Guards without Interlocks
– Apply only where more reliable
safeguards cannot be applied
– Adjustable guards
• Should be easily adjustable without
tools
• Guard should remain in place during
machine operation
– Self-adjusting guards
• Opening should be minimum required
for passage of material
29. Interlocking Guards
• Interlocking guards
– Hazardous functions cannot operate until guard is closed
– If guard is opened, stop command is given
– Closing the guard does not initiate operation
• Separate “Start” control must be operated
• Technologies available
– Mechanically activated
– Non-mechanically activated
30. Interlocking Guards with Guard-locking
• Hazardous functions cannot operate until guard is closed and
locked
• Guard remains closed and locked until hazard is removed
• Closing and locking the guard does not initiate operation
– Separate “Start” control must be operated
• Two different types
– Unconditional unlocking
• Unlocking possible at any time
– Conditional locking
• Unlocking only possible if hazard has been removed, eg
– After fixed time
– When zero speed detected
31. Sensitive Protective Devices
• Do not prevent access, but stop
movement before contact is made, eg
– Light curtains, pressure mats, trip
devices
• Not suitable when
– Parts or materials can be ejected
– Need to contain emissions (eg noise,
dust)
– Excessive or erratic machine
stopping times
– Machine cannot stop part way
through cycle
– Cannot be located with sufficient
safety distance
34. Non-mechanically Activated Interlocks
Magnet / Electronic
Proximity Systems
Plug and
Socket Systems
Control Circuit
Guard Closed
(closed circuit)
Open
Guard Open
(open circuit)
or…. current flows from male
to female part (or vice versa)
35. Q. Why do Interlocks Fail?
A. Wear and Installation Errors
• Common faults include
– Loosening of fixtures and misalignment of parts
– Sticking of moving parts
– Short circuit or open circuit
– Spring fracture
– Corrosion
• Ways to reduce likelihood of fault
– Use good quality components
– Fasten interlocks securely so do not move and do not self-loosen
– Do not use interlocks as mechanical stops
– Check installation and function as part of routine maintenance
– Test operation after installation
– Use positive mode actuation (see next slide)
– Use higher safety category of control system (see later)
36. Mechanical Interlocks
- Positive Mode Actuation
• When the guard is opened, this
movement inevitably moves the
interlock actuator along with it
– By direct contact or via rigid
elements
• When single interlock is used
should be positive mode actuation
• If >1 interlock is used, can use
combination of positive and non-
positive mode to reduce risk of
common cause failures
37. Positive Mode or Non-Positive Mode?
When guard is
closed, actuator
is depressed,
closing electrical
contacts
When guard is
opened, actuator
returns to original
position, opening
electrical contacts
Actuator
Switch containing
contacts, spring, etc
39. Q. Why else do Interlocks fail?
A. They are deliberately defeated
• Ways to minimise risk through interlock
design (General)
– Fix using fastenings that require a tool
– Locate/shield interlocks to prevent
tampering
– Use interlocks that detect if the guard is
completely removed
• Tongue-operated Systems
– Use complex shaped tongues
• Electronic/Magnetic Proximity Systems
– Use coded devices
– Incorporate obstruction to prevent
substitution of spare actuator
• Plug and Socket Systems
– Use multi-pin plugs and sockets
– Connect control circuit to both plug and
socket
40. Fault Resistance of Control Systems
• Can classify performance of safety-related control systems in
respect of resistance to faults and behaviour in fault condition
– European Standard EN 954 methodology
– 5 different categories: B, 1, 2, 3, 4
• Fault resistance is a function of:
– Hardware reliability
– System structure
– Other factors, eg maintenance, testing, software reliability
41. Category Requirements System Behaviour Principles to
Achieve Safety
B
Parts designed, constructed,
selected, assembled and combined
as per relevant standards so they can
withstand expected influences
Single fault can lead to loss of
safety function
Selection of
components
1
• As per Category B, plus…
• Well-tried components and well-
tried safety principles
Single fault can lead to loss of
safety function but probability of
fault is lower than for Category B
2
• As per Category 1, plus…
• Safety function checked at suitable
intervals by machine control system
• Single fault between checks can
lead to loss of safety function
• Fault is detected by check
System structure
3
• As per Category 1 plus…
• Single fault does not lead to loss of
safety function
• (When feasible, faults detected at
or before next demand upon the
safety function)
• When single fault occurs, safety
function is performed
• Some (not all) faults detected
• Accumulation of undetected
faults can lead to loss of safety
function
4
• As per Category 1 plus…
• Single fault does not lead to loss of
safety function
• Faults detected at or before next
demand upon the safety function,
or - if not possible –accumulation of
faults does not lead to loss of
safety function
• When faults occur, safety
function is always performed
• Faults detected in time to
prevent loss of safety function
42. Preferred Categories
Selection of Category (EN954 Method) - 1
Severity of Injury
• S1 = Normally reversible injuries
– “Insignificant”, “Minor” or “Moderate”
in Guideline 202
• S2 = Normally irreversible injuries
– “Major” or “Catastrophic” in
Guideline 202
Frequency of Exposure
• F1 = Seldom to quite often +
exposure time is short
– Up to once per hour and up to 5
minutes duration
• F2 = Frequent to continuous +
exposure time is long
– More than once per hour or more
than 5 minutes duration
43. Selection of Category (EN954 Method) - 2
Possibility of Avoidance
• P1 = Realistic chance of avoiding injury
• P2 = Avoidance unlikely
• Take into account:
– Can hazard be seen easily?
– Does person have enough time to
recognise hazard before entering
danger zone?
– Does the hazard arise quickly or
slowly?
– Could person withdraw from the danger
zone if hazard arose?
– What level of experience/expertise
would person possess?
– Information from previous incidents on
same or similar machines
Preferred Categories
45. Interventions
• Tasks that require personnel to enter a danger zone, eg
– Set-up, adjustment, clearing blockages, cleaning, line clearance,
maintenance, repair
– Tasks most likely to result in injury
• Where feasible, machinery and safeguards should be designed to
avoid the need for interventions
– ie by enabling tasks to be carried out from outside the danger zone
• Essential that interventions are carefully assessed to enable safe
systems of work to be established
46. Types of Interventions
1. “During Normal Operation” – No Disassembly
– Relatively frequent but short in duration, eg set-up, clearing
blockages, cleaning, line clearance, adjustments
– Tend to be of a ‘standard’ nature (ie same things are done each
time), clearly described in SOPs
– Typically carried out by the machine operators
– Normally can be done through interlocked guards (if correct design)
2. “Outside Normal Operation” – Disassembly
– Less frequent but of longer duration, eg cleaning, tooling changes,
modifications, maintenance, fault-finding, repair
– Tend to be more variable and are more difficult to describe in SOPs
– Mostly carried out by technicians, maintenance staff or engineers
– Normally requires lock-out / tag-out
47. Lock-out / Tag-out (LOTO)
Six Steps of LOTO:
1. Identify energy types and sources
2. Shut down machine
3. Isolate machine from energy sources
4. Install locks and tags
5. Release stored energy
6. Check effectiveness
48. Suspension of Interlocks
• Highly dangerous - should be avoided wherever feasible
• If cannot be avoided, needs multiple additional controls, eg:
– Restrict to competent persons with special training
– Should require key
• Key kept under control of authorised persons, not left in machine
– Use special safeguards, eg
• Limited-movement (“jogging”) and/or limited-speed (“inching / crawling”)
devices
– plus shrouded hold-to-run controls
– plus 2-hand activation where feasible
– Ensure emergency stops accessible
– Should only be carried out by one person from a safe position
• Barricades and warning signs
– Approach should be documented in procedure/instruction
49. Emergency Stops (e-stops) 1
• Should use positive mode
actuation
• Action should be maintained
until e-stop is manually reset
• Resetting e-stop should not
cause machine to restart
– Machine cannot restart until
all activated e-stops have
been reset
• Function/scope should be
clearly identified
Source: EN 418:1992 “Safety of Machinery – Emergency stop equipment, functional aspects – Principles for design”
50. Emergency Stops (e-stops) 2
• Should be provided for machines, except:
– Where would not reduce risk
– Hand-held or hand-guided machines
• A back-up device, not a substitute for proper safeguards!
• Should override all other commands and achieve optimal
deceleration, eg by
– Removal of power to machine actuators or mechanical disconnection
of hazardous elements from machine actuators
– May also require braking
• Types
– Initiated by a single human action, eg
• Mushroom-type push buttons (red on yellow background)
• Wires, ropes, bars, handles, foot pedals without protective covers
52. Risk Assessment Strategy
General Workplace Health & Safety Risk Assessment
Physical
Hazards
Occupational Hygiene
Hazards
Machinery Hazard
Analysis
Ergonomics
Assessment
Fire & Explosion
Assessment
Chemical Risk
Assessment
Noise Assessment
Workplace Transport Assessment
etc etc
Overall Risk Register Development (GQMP)
53. Machinery Risk Assessment
• New methodology based on current good practices
– Currently in draft: to be finalised after Network Meetings
– Longer term plan to integrate into EHS Manager
• In 6 parts
A. Information about Machine
B. Identification of Hazards
C. Analysis of Machine
D. Interlock Category Assessment
E. Machine Intervention Analysis
F. Enter in Risk Register (as per Guideline 202)
55. Workshop Tasks
In Teams
• Analyse 2 items of equipment
30 mins
– Use Machinery Safety Analysis template, etc
• Return to room: Discuss results & prepare feedback 30 mins
– Complete Risk Register template for each machine
