Cause of Device-Related Incident
Device factors; User errors

Clinical Specialty or Hospital Department
Physical Medicine / Rehabilitation

Device Factors
*Not stated; Device interaction

Document Type
Hazard Reports

External Factors
*Not stated

Mechanism of Injury or Death
Burn (electrical, thermal, chemical)

Support System Failures
*Not stated

Tampering and/or Sabotage
*Not stated

User Errors
Incorrect clinical use

Diathermy Units [11-244]; Mattresses, Operating Table [12-478]

Conductive Mattresses and Diathermy

Hazard [Health Devices Sep 1976;5(11):277]


A member hospital reported that the mattress on which a patient was receiving radio-frequency diathermy treatment began to smoke and burn. The treatment was discontinued, and no injuries resulted. Subsequent investigation disclosed that the mattress was the conductive type usually found in operating suites. Absorption of radio-frequency energy by the mattress caused the dangerous temperature rise, and, as a side effect, drastically diminished the therapeutic energy being delivered to the patient.


The radio-frequency electromagnetic field produced by diathermy units heats the treated areas of the patient's body by inducing electrical currents to flow in the irradiated tissues. The electromagnetic field is strongest near the application head and the power cables feeding them but also pervades the entire area surrounding the operating diathermy unit. Any conductor placed within this field will be heated, the degree of heating depending on the local field strength and the conductor properties. For this reason, diathermy manufacturers caution that all metal and other conductors be removed from the treatment area.

Conductive mattresses are included in this caution but may not be recognized as sources of danger, as is evident in the reported incident. In this case, the cables powering the applicator head rested against the mattress and caused it to overheat.


  1. Inspect the mattresses used on your diathermy treatment tables to determine if they are conductive. Conductivity may be indicated by a label on the mattress.
  2. If no label is present, test for mattress conductivity using a megohmmeter identical to that used in testing operating room floors. A rough measurement can be made using an ohmmeter and standard banana plugs or clip leads contacting two points on the mattress about six inches apart. Be sure not to touch exposed metal on these meter leads with bare hands. If the meter needle swings appreciably (to approximately 10-50 kilohms), the mattress is conductive.
  3. Replace all conductive mattresses on diathermy treatment tables with ones that are nonconductive.


  • Diathermy Units [11-244]
  • Mattresses, Operating Table [12-478]

Cause of Device-Related Incident

Device factor: Device interaction

User error: Incorrect clinical use

Mechanism of Injury or Death

  Burn (thermal)

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