C6.3 Protective measures

Question 1

Guarding requirements

Answer 1

suitable
good construction
in good repair
efficient working order
no additional risk
not easily disabled / bypassed
at a distance from danger zone
not unduly restrictive
permit maintenance
prevent contact
secured to machine
protect so that objects cannot fall onto moving parts
introduce no new hazards
do not interfere with the work
allow safe lubrication

Question 2

PUWER Reg 11 hierarchy of guarding

Answer 2

Fixed or enclosed guards
Interlocking guards or auto devices
Appliances, eg push sticks
Training, info, instruction, supervision

Question 3

Types of guards

Answer 3

Fixed
Interlock
Automatic
Trip

Question 4

Fixed enclosed guards

Answer 4

denies access to danger at all times
fixed to machine
need tool to remove
openings must not lead to danger

Question 5

Adjustable guard

Answer 5

adjustable bars to allow workpiece only to enter

adjusts to allow variety of workpieces

Question 6

self adjusting guard

Answer 6

barrier moves dependent on size of workpiece

eg circular saw

Question 7

Two hand control

Answer 7

both hands needed on controls to operate
constant correct pressure
hands in a safe location

Question 8

Interlocked guard

Answer 8

machine cannot operate when access available to danger zone
guard closed = machine can operate
operates by limit switches
fail to safe
electrical
mechanical
hydraulic
pneumatic

Question 9

automatic guard

Answer 9

sweeps danger zone clear

Question 10

photoelectric devices

Answer 10

light curtain beam

machine stops if broken

Question 11

capacitance field

Answer 11

machine stops if electric field broken

Question 12

pullback devices

Answer 12

cables connected to operators hands
used with machine with stroke action
access allowed when device is up
hands pulled back as device descends

Question 13

restraint device

Answer 13

hands attached to cables that restrain where hands can go

Question 14

trip wire

Answer 14

pull wire to stop machine

Question 15

gates

Answer 15

machine only operates if gate closed

Question 16

robots

Answer 16

repetitive processes
prevent injury from repetition
use where unsafe / hazardous / unpleasant tasks

Question 17

protective shields

Answer 17

protection from flying particles / substances

Question 18

holding tools

Answer 18

used to place / remove items in danger zone

use as an additional control, not in place of

Question 19

guard considerations

Answer 19

prevent any part of body reaching danger zone
any opening at distance to prevent reaching danger zone
ability to withstand force of ejection
protect against hazards identified
weight / size of guard
compatible with material being processed
resistant to possible contaminants

Question 20

fixed distance guards

Answer 20

does not completely cover danger zone but places it out of reach

Question 21

barrier considerations

Answer 21

height and distance to prevent reaching danger zone

1.8 metres for perimeter fencing

Question 22

interlocks - sensing devices

Answer 22

rotating sensing
light beam
proximity device
position switch

Question 23

interlocks - timing devices

Answer 23

mechanical, electric, electronic clock
delay relay
sequence valve
threaded bolt

Question 24

interlock failure mechanisms

Answer 24

failure / interruption of power supply
wiring malfunction
earthing fault
cross connection
electrical interference
disconnection of hose / pipe
mechanical failure
brake failure

Question 25

interlock failure controls

Answer 25

dual control system with / without cross monitoring

Question 26

normally open limit switch

Answer 26

spring keeps contact open
easy to defeat
broken spring = switch is on
can jam in on position

Question 27

normally closed limit switch

Answer 27

spring closes contact
difficult to defeat
fails to safe
wear / misalignment = fail to danger
switch active if guard removed = danger

Question 28

positive & negative limit switch in series

Answer 28

very difficult to defeat
rigorous maintenance needed
monitor switches with warning lights

Question 29

interlock switch types

Answer 29

cam operated switch
tongue operated switch
captive key switch
trapped key
proximity switch
magnetic switch
diode link
manually operated delay bolt
solenoid operated shot bolt

Question 30

cam operated position switch

Answer 30

movement of guard from safe position causes switch plunger to be depressed and trip the controls

Question 31

magnetic switch

Answer 31

actuating magnet attached to guard

easily defeated

Question 32

captive key system

Answer 32

guard has to be closed before key can be put in lock

Question 33

trapped key system

Answer 33

removable key trapped in lock

when guard closed, key can be removed

Question 34

pressure sensitive mat

Answer 34

pressure sensors - equipment operates when activated
can be damaged
mat of suitable dimension that person cannot reach danger zone when standing on mat

Question 35

reasons why light beam cannot be used

Answer 35

slow machine response time
poor brake design
variable machine speed
machine cannot stop part cycle
machine is part of production line
stored energy
machine can eject parts

CAN be used in conjunction with other means to control risks

Question 36

mechanical restraints

Answer 36

mechanical restraint to dangerous parts to prevent it moving

relies on strength of restraint

Question 37

jigs

Answer 37

used to hold / move workpiece keeping body away from danger zone
used in addition to guards

Question 38

push sticks

Answer 38

used to feed timber into circular saws

used to push food into food processing machine