ELECTRICAL SAFETY DEVICES Flashcards
What are the categories of equipment hazards in radiography?
- Mechanical hazards (e.g., tilting tube)
- Electrical hazards (e.g., short circuit)
- Radiation hazards (e.g., tube leakage)
- Other hazards include burning/overheating and equipment operation below acceptable standards.
What mechanisms are put in place to prevent electrical hazards in radiography equipment?
- Use of switches, circuit breakers, and fuses
- Mobile units have sockets with a switch in their live line to switch off the supply before removing the plug top
- Fuses prevent drawing excessive current
- Static X-ray equipment has an isolator switch to completely break the electrical connection
How are current-carrying components protected in radiography equipment?
- Covers are placed around electrical parts with components mounted on insulating material
- High tension equipment is enclosed in an earthed metal cover to avoid arcing
- Locks with keys ensure the unit is only opened by approved persons and disconnect the electrical supply when the key is turned
- All conductors are covered with an insulating sleeve
- High voltage cables have an earthed outer sheath for greater protection
How is isolation of high tension (HT) circuits achieved in radiography equipment?
- HT circuits are operated remotely through a low tension circuit
- Subsidiary circuits and controls operate at 240 volts or below
- The secondary coil of the HT transformer is in two halves, with the center point earthed
- HT transformer and filament transformer primary windings are isolated from their secondary windings
What is the purpose of earthing in radiography equipment?
- All equipment is earthed to provide a very low resistance pathway to the earth
- Fixed units have an earthing conductor connected directly to the earth
What is the purpose of switches (sensors) in radiography equipment?
Installed on targeted areas to stop motor-driven movement when a collision would occur.
EXAMPLES IN RADIOGRAPHY WHERE UNNECESSARY MOVEMENT OF THE MACHINE IS STOPPED BY SENSORS
Examples include:
* On a tilting table to stop the tilt if the longitudinal movement is too great.
- On the collimator of a ceiling-suspended X-ray tube to prevent downward drive if it touches an obstruction.
- On mobile machines to inactivate motion upon sensing an obstruction.
How do covers protect against mechanical hazards in radiography equipment?
- Covers are placed around moving parts to prevent injury by preventing access.
- Used in CT scans, mammography, and X-ray units.
- Modern units use sensor-generated circuits and minicomputers to anticipate and avoid collisions.
What measures are taken to protect against unnecessary radiation in radiography equipment?
- Shielding against primary radiation with lead-lined X-ray tube shields.
- Collimators to limit the size of the primary beam.
- Interlock circuits to prevent X-radiation if the primary barrier is not in place.
- Mechanical linking between the X-ray tube and image intensifier to ensure proper beam direction.
How is the length of X-ray exposure and tube current controlled?
- Fluoroscopy time is measured by a timer that audibly indicates and cuts off radiation when a preselected time is reached.
- Fluoroscopic mA controls have restrictors to prevent excessive mA selection, generally a 3 mA maximum.
- Guard timers cut an exposure not terminated by an automatic exposure control.
What restrictions are in place to prevent short focus-to-skin distance in radiography?
- Mechanical blocks prevent the tube from coming too close to the patient during fluoroscopy.
- Tilting table height adjustment ensures an acceptable focus-to-table top distance.
- Mechanical linking of tube and film support prevents too short a distance.
- Face pieces on X-ray tubes prevent the source of radiation from being too close to the patient.
What indicators are used to reduce human error in radiography equipment?
- Indicator lights over entrance doors show when X-rays are being generated.
- Indicator lights on the tube show which tube is being energized.
- Indicator lamps on the console show selected factors and accessories.
- Interlock systems ensure the correct setting of the technique.
How is personnel protected against burning or overheating in radiography equipment?
Light beam diaphragm high intensity bulb has a timer switch to prevent metal covers from becoming excessively hot.
What mechanisms protect radiography equipment from burning or overheating?
- Interlock circuits prevent tube damage from overheating due to excessive input load.
- Indicator systems display the heat level at the tube anode.
- Rating charts enable safe exposure factor selection.
- Thermal cut-out switches prevent parts from overheating, such as the X-ray tube thermal cut-out operating if the oil becomes excessively hot.
What safety devices prevent the use of radiography equipment that has not reached acceptable standards?
- Delay circuits allow time for tube filaments to reach operating value, anode to reach correct rotation speed, and auxiliary equipment to reach operational standards.
- Covers prevent dust accumulation on sensitive components.
