4 Electrostatic hazards

4.1 General

Four different hazards of static electricity are generally recognized: ESD damaging ordisrupting electrical equipment, contamination caused by ESA, igniti on of flammable substances and electrosta tic shock to peopl

4.2 ESD effects on equipment

Electrostatic discharges cancause losses of the functions of instrumentation during patient care increasing the risks to human safety. Insufficient electrostatic control may also cause unnecessary repair costs of medical equipment, as well as corruption of data affecting the quality and reliability of medical operation.

Electrical installation requirements for medical equipment and locations are provided in the electrical safety rules specified in IEC 60364(all parts)[3]. It is essential to recognize that electrical safety does not necessarily provide precautions for prevention of the risks of static electricity and electrostatic discharge (ESD).Local safety regulations shall be taken into account.

ESD immunity testing does not cover all the real discharge scenarios,such as those where metal partshaving different electric potentials are touched together. A current limiting resistor used in the ESD testing specified in IEC 61000-4-2 [4] does not necessarily exist in such situations, resulting inhigher discharge power in equipment under real stress. Charge accumulation in a mobile metal object can also result in high energies in uncontrolled environments. Especially in low humidity, discharge energies can exceed the stress levels used in IEC 61000-4-2 [4]. 

A completely integrated system in medical care is not necessarily tested against transients caused by ESD, although individual parts of the system have passed EMC qualification. Therefore, it does not always take into account all the realistic coupling and failure scenarios of the whole system.

Discharges from isolated conductors or from a human body can beprevented with grounding. Conductive parts of patient beds, intravenous stands, trolleys, delivery carts, over-bed tables, chairs, and other mobile metal objects are not normally connected to the protective earth. Therefore, grounding all conductive partsof every item through the flooring or with direct electrical connection to a functional ground becomes essential for static control.

The probability of ESD can efficiently be reduced by optimization of humidity levels, bipolar ionization,adequate material selection, personnel grounding, and grounding of mobile metal objects. In general, the prevention of static charge generation and ESD is preferable compared to enhancing medical equipment EMC immunity.

If a functional ground is used for electrostatic control purposes, it should be electrically bonded to protective earth where possible so as to avoid potential differences between the two systems.

4.3 Contamination caused by ESA

Electrostatically charged surfaces attract airborne particles. Increased depositionof microorganisms onto charged surfaces, including the airways, human skin, and open wounds, can contribute to the incidence of hospital infections. Electrostatic sources of contamination and nosocomial infection can be healthcare personnel, patients, or the environment. All objects that come into contact with patients can be considered as potentially contaminated.

Cleaning, disinfection and sterilizing can prevent transmission of infective agents. However, because of the human factor, complete certainty in cleanliness cannot be achieved without adequate control of the environment. Avoidance of electrostatic attraction (ESA) decreases airborne microbe contamination and improves overall cleanliness in healthcare. The reduction in charge carried by airborne submicron contaminants will additionally reduce the deposition of such contaminants in the airways, thereby reducing the load placed on the body’s immune system. Charge accumulation and high surface charge densities can be reduced to tolerablelevels by grounding of personnel and other conductors, and by correct selection of materials.

4.4 Ignition of flammable substances

The use of flammable substances in healthcare facilities has decreased, but the risk of fires and explosions can still occur especially in laboratories, intensive care units and operating rooms. For example, using alcohol based sterilizing substances has caused fires due to electrostatic discharge. ESD can be an ignition source in hyperbaric oxygen facilities and other locations where the oxygen concentration exceeds 23,5 % by volume.

The risk of incendiary ESD can be reduced to tolerable levels by grounding of personnel and other conductors, and by correct selection of materials.

4.5 Electrostatic shock to people

The incidence of unpleasant electrostatic shocks to peoplehas increased due to the increased use of highly insulating materials such as plastics. Anelectrostatic discharge occurs when a human body approaches close enough to an object with different electric potential to exceed the electric breakdown field strength. ESD energy can be high enough to cause painful sensations to patients and healthcare personnel, resulting in involuntary movements, which can lead to accidents.

The risk of electrostatic shock can be reduced to tolerable levels by grounding of personnel and other conductors, and by correct selection of materials

5 Electrostatic control requirements

5.1 General

Electrostatic control requirements in healthcaredepend on the medical procedures, locations and activities such as service and maintenance of medical equipment.

5.2 Medical procedures 

To ensure safetyof patients from electrostatic hazards, protective measures shall be applied during medical examination and treatment.

Medical procedures can require specific electrostatic control actions that are dependent on the particular requirements of instrumentation, electric equipment or cleanliness. When protective measures have not otherwise been specified, the requirements in 5.3 to 5.7 shall be applied. Consideration shall also be given to applying the recommendations in 5.3 to 5.7a nd Annex B. 

5.3 Medical locations

5.3.1 Classification by groups 

Locations that are intended for purposes of diagnosis, treatment, monitoring and care of patients shall be classified in the following groups, as defined in IEC 60364-7-710: unclassified, G0, G1 and G2.

Selection of materials to reduce residual charge levels is recommended in all locations. Grounding of personnel and other conductors is recommended in G0 and G1 locations, and is required in G2 locations. Electrostatic control methods for each location are summarised in Table 1.