MNB.22 Electrical Safety PDF

Musculoskeletal System, Nervous System & Bioelectricity MNB.22 Electrical Safety INGMAR SCHOEN D AT E : 5 - D E C - 2 0 2 4 Learning outcomes At the end of this lecture, the learner will be able to Identify potential hazards associated with static electricity, AC current, and microshock sensit...

Musculoskeletal System, Nervous System & Bioelectricity MNB.22 Electrical Safety INGMAR SCHOEN D AT E : 5 - D E C - 2 0 2 4 Learning outcomes At the end of this lecture, the learner will be able to Identify potential hazards associated with static electricity, AC current, and microshock sensitive patients. Discuss precautions to manage static electricity. Discuss precautions to counteract accidental electric shock by AC current, including fuses and ground fault interrupters. Discuss the management of microshock sensitive patients. MNB.22 Electrical Safety 2 Static electricity MNB.22 Electrical Safety 3 Build up of static electricity Electrostatic effects are much more prominent in dry conditions (low humidity) since any moisture in the air can Dry air Humidified air drain away excess charge through attachment to the water molecules. MNB.22 Electrical Safety https://www.youtube.com/watch?v=ekPzRThYzU0 4 Static electricity hazard: ‘Sparking’ The build-up of static electricity can cause ‘sparking’ during discharge, and therefore poses a risk in the presence of flammable gases (i.e. oxygen or anaesthetic gases) - requires precautions. MNB.22 Electrical Safety https://www.youtube.com/watch?v=IdcPeW1XwKs 5 Precautions to handle static electricity Maintain humidifiers in operating theatres. Anyone likely to pose a static discharge threat, Surgical gowns should be treated with silicone, should discharge before entering oxygen tents and clothing materials should be natural (e.g. etc. (How?) cotton) – not synthetic. All electrotherapy or ICU equipment should be Use of anti-static flooring. properly earthed. (Why?) Use of anti-static rubber for masks, tubing, trolley wheels, stool seats, boots etc. MNB.22 Electrical Safety 6 Electrical appliances What should we do to minimise the risk when working with electrical equipment? MNB.22 Electrical Safety 7 Electrical appliances Most domestic supplies have three terminals: Live, Neutral, and Earth. Earth Appliance The potential difference (voltage) is applied between the live and neutral, while the earth is usually connected to the casing of an appliance Neutral as a safety mechanism. Mains electric supply in the UK/Ireland (or Live Bahrain or Malaysia) is 50 Hz, 220/240 V, while in the US it is 60 Hz at 110 V. MNB.22 Electrical Safety 8 Hazard related to AC current sources Mains power If a person accidentally touches a live wire, they provide a closed link to earth and current flows through them. Note, ground (or earth) is common to both the person and the electrical socket. MNB.22 Electrical Safety 9 What is the danger of short circuit?? 2-pin plug This exists where there is a breakdown in insulation between the live wire and the casing of the appliance. The appliance may work OK and will look normal. However if you touch it, the current will flow through you to earth rather than flowing through the appliance which may have a higher resistance. Note: Device uses a 2-pin plug! MNB.22 Electrical Safety 10 Precaution against short circuit 3-pin plug If the casing is connected directly to earth, then any ‘leakage’ current will flow immediately back to earth through this connection and lessen the risk of electrocution, i.e. Note, 3-pin plug MNB.22 Electrical Safety 11 Simple precautions to minimise accidental exposure to electric current All appliances with metal casing should be properly earthed. Where possible, patients should not be grounded (e.g. choice of bed etc.). MNB.22 Electrical Safety 12 Precautions when using a defibrillator (refer to MNB.20 for details on defibrillator) Large area paddles must be used to prevent unwanted burns. (Why??) Both electrodes (paddles) must be isolated from ground before charge and discharge. The patient must not be in contact with ground. (Why??) Physical contact with the patient must not occur during defibrillation. (Why??) Any monitoring equipment (e.g. ECG) must be isolated and current protected. MNB.22 Electrical Safety 13 Simple Safety Devices MNB.22 Electrical Safety 14 Fuses Arial 20 pt What fuse should I use? A fuse is a simple device which is connected in Use P = IV to calculate series with any appliance so that all of the the current drawn by a current flows through it. device, where V = 240 V The fuse consists of a thin wire with a low in Ireland and P is the melting point, which will melt when the current power usage of the device. exceeds a pre-determined threshold. When the The fuse rating should be slightly higher than wire melts, the circuit is broken and current the current drawn!! stops flowing. MNB.22 Electrical Safety 15 Ground Fault Interrupter (GFI) Leakage currents are currents that flow to the case of an appliance due to a partial breakdown of the insulation between the live wire and the case. A GFI checks and compares the current flowing to an appliance through the live wire with that returning through the neutral wire. If these are different, this indicates a hazardous ‘leakage current’. If the difference is greater than ~5 mA, the GFI will ‘break’ open the circuit and halt the flow of current. (Why 5 mA??) MNB.22 Electrical Safety 16 Microshock Hazard MNB.22 Electrical Safety 17 What does microshock hazard mean? (refer to MNB.19 and MNB.20) In previous discussions regarding the This means that currents as low as 20 µA physiological effect of exposure to electric could induce fibrillation if the current is current, it was assumed that the current was introduced directly into the heart. distributed throughout the body. [For a resistance = 1000 Ohms, this current If an ‘internal’ electrical path to the heart exists, could be produced with a voltage as low as the danger levels for current shock could be 20 mV, i.e. 0.02 V!!] reduced by a factor of ~1000. MNB.22 Electrical Safety 18 The path taken by a current Who is microshock sensitive? Patients with: Pacemakers Inserted catheters Any internally placed conductor The second condition for microshock risk is that the patient is grounded in some way. If this is the case, the connection to ground provides a path for the current to flow through the patient. MNB.22 Electrical Safety 19 Precautions for microshock sensitive patients Hence, microshock sensitive patients must be completely isolated from ground at all times. It is also very important that all electrical equipment connected to (or close to) the patient must be individually earthed. MNB.22 Electrical Safety 20 Thank you F O R M O R E I N F O R M AT I O N P L E A S E C O N TA N T INGMAR SCHOEN EMAIL: [email protected] 21