IEC 60601-1 - Medical Electrical Equipment Safety 11.2: 11.2 Fire prevention

Enclosures have the strength and rigidity to avoid fire from total or partial collapse under reasonably foreseeable misuse, checked by the 15.3 mechanical tests. In an oxygen-rich environment the risk of fire is reduced as far as possible in normal and single fault condition (the 13.1.1 requirements suffice up to 25 percent oxygen or 27.5 kPa partial pressure): an unacceptable risk exists where a source of ignition contacts ignitable material with nothing to limit spread, a source of ignition existing where material reaches its ignition temperature, solder joints could loosen or short, parts crack or deform exposing over 300 degrees or sparks, parts exceed 300 degrees, or sparks exceed the Figure 35 to 37 energy limits (worst case 100 percent oxygen, solder contacts, cotton fuel, deviations justified in the file), the alternative being the spark ignition test with pins of the actual contact material flushed with oxygen over at least 300 trials and a safety margin factor of three. Acceptable residual risk is provided, alone or combined as the risk management process determines, by limiting the power supplies of components in an oxygen-rich compartment below ignition energy, by ventilating compartments that could be penetrated by oxygen so that concentration stays under 25 percent at the minimum operator-detectable leak, by sealing all joints and holes between an ignition-capable compartment and the oxygen-rich one with maintenance intervals set by risk assessment, or by enclosing single-fault ignition sources so that a fire self-extinguishes rapidly with no hazardous toxic gas reaching the patient, tested by igniting a fire inside the enclosure. External oxygen exhaust outlets are not placed where externally mounted electrical components could ignite them, oxygen at the component staying under 25 percent; electrical connections in an oxygen-rich compartment do not spark by loosening or breaking unless energy-limited, screws being secured by varnish, spring washers or torque and exiting cable connections having additional mechanical fixing; and the single fault conditions for oxygen-rich environments are failure of the ventilation, of the barrier, of a component creating an ignition source, of insulation providing one but not two means of patient protection, and of a pneumatic component leaking oxygen-enriched gas.