C6.3 Protective measures Flashcards
Guarding requirements
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
PUWER Reg 11 hierarchy of guarding
Fixed or enclosed guards
Interlocking guards or auto devices
Appliances, eg push sticks
Training, info, instruction, supervision
Types of guards
Fixed
Interlock
Automatic
Trip
Fixed enclosed guards
denies access to danger at all times
fixed to machine
need tool to remove
openings must not lead to danger
Adjustable guard
adjustable bars to allow workpiece only to enter
adjusts to allow variety of workpieces
self adjusting guard
barrier moves dependent on size of workpiece
eg circular saw
Two hand control
both hands needed on controls to operate
constant correct pressure
hands in a safe location
Interlocked guard
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
automatic guard
sweeps danger zone clear
photoelectric devices
light curtain beam
machine stops if broken
capacitance field
machine stops if electric field broken
pullback devices
cables connected to operators hands
used with machine with stroke action
access allowed when device is up
hands pulled back as device descends
restraint device
hands attached to cables that restrain where hands can go
trip wire
pull wire to stop machine
gates
machine only operates if gate closed
robots
repetitive processes
prevent injury from repetition
use where unsafe / hazardous / unpleasant tasks
protective shields
protection from flying particles / substances
holding tools
used to place / remove items in danger zone
use as an additional control, not in place of
guard considerations
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
fixed distance guards
does not completely cover danger zone but places it out of reach
barrier considerations
height and distance to prevent reaching danger zone
1.8 metres for perimeter fencing
interlocks - sensing devices
rotating sensing
light beam
proximity device
position switch
interlocks - timing devices
mechanical, electric, electronic clock
delay relay
sequence valve
threaded bolt
interlock failure mechanisms
failure / interruption of power supply wiring malfunction earthing fault cross connection electrical interference disconnection of hose / pipe mechanical failure brake failure
interlock failure controls
dual control system with / without cross monitoring
normally open limit switch
spring keeps contact open
easy to defeat
broken spring = switch is on
can jam in on position
normally closed limit switch
spring closes contact difficult to defeat fails to safe wear / misalignment = fail to danger switch active if guard removed = danger
positive & negative limit switch in series
very difficult to defeat
rigorous maintenance needed
monitor switches with warning lights
interlock switch types
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
cam operated position switch
movement of guard from safe position causes switch plunger to be depressed and trip the controls
magnetic switch
actuating magnet attached to guard
easily defeated
captive key system
guard has to be closed before key can be put in lock
trapped key system
removable key trapped in lock
when guard closed, key can be removed
pressure sensitive mat
pressure sensors - equipment operates when activated
can be damaged
mat of suitable dimension that person cannot reach danger zone when standing on mat
reasons why light beam cannot be used
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
mechanical restraints
mechanical restraint to dangerous parts to prevent it moving
relies on strength of restraint
jigs
used to hold / move workpiece keeping body away from danger zone
used in addition to guards
push sticks
used to feed timber into circular saws
used to push food into food processing machine
