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Hot Wire Cutters - Safety

Hot wire cutters use low voltage electricity to heat a wire thus allowing it to melt its way through polystyrene foam. Because a low voltage is used there is no risk of electric shock. Neither is the wire capable of cutting your fingers, but it will burn them and anything else that you allow to come into contact with it.

The main issue with hot wire cutter safety relates to the toxic fumes which can be given off when polystyrene foam (Styrofoam) is melted. We have tracked down some definitive advice about this and we present it below. The bottom line seems to be that in hobby use, with sensible ventilation, the risks are manageable.


This information is from 'Risk Assessments for Secondary Schools' and is published by the Consortium of Local Education Authorities for the Provision of Science Services (CLEAPPS), Brunel University, Uxbridge, England UB8 3PH. Brunel is one of the premier technological universities in the UK. This is a publication advising English science teachers about classroom hazards.


The cutting of expanded polystyrene by means of a wire heated to about 300 degrees C.


Harmful: hazardous by inhalation; Irritant: Styrene fumes can irritate the eyes.

Risk Assessment:

Harmful: Styrene fumes are produced as the material degrades when overheated. Styrene has a MEL (Maximum Exposure Limit) of 100ppm (parts per million, 8 hour Time Weighted Average) and 250ppm (15 minute reference period). However, the process is safe with up to 5 cutters in simultaneous use in a well-ventilated workshop. Irritant: The eye irritation becomes severe only at exposures of 200ppm and above but eyes may water at levels below the MEL.

Control Measures:

Small, hand-held cutters may be used in well ventilated conditions. Large, bench-mounted types may require local exhaust ventilation: a special assessment is necessary. The ventilation required to control the toxic hazard will also control the irritant one.

Further information:

Small quantities of styrene fumes are produced as the material degrades when overheated. The odour of styrene can be detected at very low levels, well below the MEL of 100ppm. The fumes can cause dizziness and children are particularly vulnerable to high concentrations. However, measurements while using a hand-held cutter have shown that with reasonable ventilation and moderate care, styrene levels in the operator's breathing zone are less than 10% of the MEL.

The process does not require the material to be heated beyond its melting point. In practice, because the wire has a very low thermal mass, its temperature tends to rise very rapidly when it is not being constantly cooled by the feed of the material being cut.

On a basic bench machine with no means of quickly disconnecting the heating power to the wire, residual material adhering to the wire at the end of the cutting operation will quickly overheat and, in small quantities, degrade to produce styrene fumes. Effective ventilation must sweep these away immediately. It is important to ensure that the equipment operates at the lowest temperature that allows free cutting. Controlled electrical heating is desirable to obtain an even wire temperature. If smoke is given off, the wire is too hot. Some bench hot-wire cutters have a foot switch which, if correctly used, will virtually eliminate the production of harmful fumes.

Immediate Remedial Measures:

If styrene fumes are inhaled remove the person to fresh air and seek medical advice.

If in eyes: If eyes water due to styrene fumes, flush with water and remove person to fresh air. If the condition persists seek medical advice.

Gary's comment:

When using a hot wire cutter I now open windows or do it out of doors. My cutter has a push-button switch and I release it immediately when finishing the cut and scrape off any blobs of polystyrene. I feed the material through steadily and don't allow the wire to stay in one place, which overheats the foam and produces fumes. If I feel the fumes are building up or I feel nauseous I take a break and get some fresh air.

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