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Health Canada Safety Code 6 (2015)—Limits of Human Exposure to Radiofrequency Electromagnetic Energy in the Frequency Range from 3 kHz to 300 GHz

Preview: Learn more about Health Canada Safety Code 6 and the Canadian limits for human exposure to radiofrequency electromagnetic energy.

Health Canada Safety Code 6 establishes Canadian limits for human exposure to radiofrequency electromagnetic energy from 3 kHz to 300 GHz. The 2015 edition was prepared by Health Canada’s Consumer and Clinical Radiation Protection Bureau and replaced the 2009 version. It specifies maximum exposure levels for controlled and uncontrolled environments and provides the scientific and dosimetric framework used in Canadian RF safety and regulatory practice.

The Code applies to people working at or visiting federally regulated sites. Its limits may also be adopted by provinces, industry, and other authorities. The 2015 document records that it was adopted as the scientific basis for federal equipment-certification and RF exposure-compliance requirements governing wireless devices and infrastructure, including mobile phones, base stations, and broadcast antennas.

Purpose, scope, and exclusions

The purpose of Safety Code 6 is to prevent established adverse human health effects from RF exposure in both controlled and uncontrolled environments. It applies independently of the source: the same health-based limits can be used for telecommunications, broadcasting, radar, industrial RF equipment, medical and scientific equipment, consumer devices, and other emitters within the frequency range.

The Code does not apply to deliberate exposure of patients for medical treatment performed by or under the direction of a medical practitioner. It is also not a product-performance specification. It states limits on human exposure; separate equipment, measurement, installation, and certification standards determine how a particular product or facility demonstrates compliance.

The document recognises that unusual technologies and exposure scenarios may require interpretation. It cannot prescribe a complete procedure for every source geometry, waveform, or task. Appropriate technical standards, competent assessment, and consultation with the responsible authority may therefore be required in special cases.

The preface also records a specific qualification for the Department of National Defence: it is to conform to the Code except where it considers compliance detrimental to activities supporting Canadian Forces training and operations. This provision should not be interpreted as removing the need for military risk management or suitable force-health-protection controls.

Scientific basis

Safety Code 6 uses a weight-of-evidence review of peer-reviewed scientific research. Health Canada distinguishes established adverse health effects from reported biological responses that lack sufficient evidence of causality, biological plausibility, or reproducibility. The 2015 Code identifies tissue heating and stimulation of excitable tissue as the established adverse effects relevant to acute exposure between 3 kHz and 300 GHz.

The limits are based on the lowest exposure levels at which established adverse effects occur and incorporate safety margins intended to keep permitted exposure below thresholds for harm. The Code states that, based on the evidence reviewed for the 2015 edition, there was no scientific basis for acute, chronic, or cumulative adverse health risk below its limits.

This scientific conclusion is tied to the edition and evidence considered at the time. Health Canada describes the Code as subject to continuing review and periodic revision. Users should therefore verify the applicable federal or provincial requirements and any later supplementary guidance rather than assuming that every 2015 procedure remains the current administrative method.

Controlled and uncontrolled environments

Safety Code 6 defines a controlled environment by three cumulative conditions. First, RF field intensities in the area have been adequately characterised through measurement or calculation. Second, exposed persons are aware of the potential for RF exposure and understand the field intensity in their environment. Third, those persons understand the potential health risks and can control their risk through mitigation strategies.

If any of these conditions is not satisfied, the environment is uncontrolled. An uncontrolled environment can therefore include a workplace where fields have not been properly assessed, where people lack suitable RF safety training, or where they cannot evaluate or mitigate their exposure. The distinction is based on knowledge, characterisation, and control rather than simply on whether a person is an employee.

Controlled-environment limits are higher because they assume an assessed setting and informed people who can use effective controls. Uncontrolled limits are more restrictive and apply to the general public, visitors, untrained personnel, and other circumstances in which those assumptions cannot be made. Neither category permits exposure above its applicable maximum limits.

Basic restrictions and reference levels

The Code uses two related levels of protection. Basic restrictions are quantities within the body directly linked to established adverse effects. They are expressed as internal electric-field strength at lower frequencies and specific absorption rate (SAR) where energy absorption and heating are relevant.

Reference levels are expressed in quantities that can generally be measured or calculated outside the body: unperturbed electric- and magnetic-field strength, power density, induced current, and contact current. They were derived from dosimetric analyses connecting external fields with the underlying basic restrictions.

Compliance with the applicable reference levels normally demonstrates compliance with the corresponding basic restrictions. Exceeding a reference level does not necessarily mean that a basic restriction has been exceeded. A more detailed measurement, calculation, or dosimetric assessment may demonstrate compliance, particularly in non-uniform or unusual coupling conditions.

Internal electric field and nerve stimulation

Between 3 kHz and 10 MHz, basic restrictions on internal electric-field strength protect against stimulation of excitable tissues. Sufficiently strong internal fields can alter membrane potentials and initiate unwanted nerve or muscle responses. The restrictions are specified as instantaneous rms values within excitable tissue, with different limits for controlled and uncontrolled environments.

Where internal electric field cannot be determined practically through measurement or modelling, the external-field reference levels must be assessed. In the transition region, the assessor cannot consider stimulation and heating independently: both sets of applicable restrictions may need to be satisfied.

Specific absorption rate

Between 100 kHz and 6 GHz, SAR basic restrictions protect against whole-body heat stress and excessive localised heating. Whole-body average SAR is limited to 0.08 W/kg in uncontrolled environments and 0.4 W/kg in controlled environments. These values incorporate safety factors below the whole-body level associated with a significant rise in core temperature.

Localised SAR limits address hot spots. For the head, neck, and trunk, peak spatial-average SAR is limited to 1.6 W/kg in uncontrolled environments and 8 W/kg in controlled environments, averaged over any 1 g cube of tissue. For the limbs, the corresponding limits are 4 W/kg and 20 W/kg, averaged over any 10 g cube of tissue.

SAR limits take precedence over field-strength and power-density reference levels between 100 kHz and 6 GHz and must not be exceeded. The Code indicates that SAR should be determined where exposure occurs within 0.2 m of a source. If SAR assessment is impractical, compliance is assessed using the applicable external-field or power-density reference levels, subject to the conservative assumptions on which those levels are based.

Exposure above 6 GHz

Above 6 GHz, RF energy is absorbed predominantly in superficial tissues such as the skin and cornea. The 2015 Code considers incident unperturbed power density, with derived electric- and magnetic-field strengths, more appropriate than whole-body or cubically averaged SAR for this range.

Safety Code 6 therefore uses field-strength and power-density limits through 300 GHz. Their numerical values are frequency dependent and include specified spatial and temporal averaging conditions. Modern close-proximity or highly directional devices may also be subject to later regulatory or technical procedures that supplement the 2015 framework.

Reference levels and field regions

The reference-level tables cover electric- and magnetic-field strength from 3 kHz to 10 MHz, electric- and magnetic-field strength and power density from 10 MHz to 300 GHz, and induced and contact currents from 3 kHz to 110 MHz. Different values and averaging rules apply to controlled and uncontrolled environments.

In the far field, electric-field strength, magnetic-field strength, and power density are related through the impedance of free space, so one quantity can be used to derive the others. In the near field, those simple relationships may not apply and both electric and magnetic fields generally require assessment. Antenna size, wavelength, distance, reactive coupling, and surrounding structures determine the field region.

Where fields are spatially non-uniform, averaging is permitted only under the conditions specified by the Code and only if the sampling procedure ensures that the relevant basic restriction is not exceeded. In some circumstances the spatial peak, rather than an average over a convenient survey area, must be compared with the reference level.

Temporal averaging and short exposures

For SAR-based restrictions and reference levels, the principal averaging period is six minutes. A varying or intermittent field can exceed the long-term reference value for part of that interval only where the specified time average remains within the limit and any separate instantaneous or peak requirement is also satisfied.

The assessment must account for transmitter on and off periods, duty factor, beam direction and sweep time, power control, pulse characteristics, and source variability. A short measurement taken during low traffic or an unfavourable point in a scanning cycle may not represent the relevant maximum or time average.

Pulsed exposures are subject to additional peak-related provisions. Time averaging cannot be used to disregard a requirement intended to prevent stimulation, perception, shock, burn, or another effect governed by an instantaneous value.

Multiple frequencies

Safety Code 6 includes summation rules for simultaneous exposure at several frequencies. Each field or current component is normalised to its applicable frequency-dependent reference level and combined according to whether nerve stimulation or SAR is the controlling mechanism.

In the 100 kHz to 10 MHz transition range, both stimulation-based and SAR-based summations may be required. A multi-service site cannot be considered compliant merely because every transmitter is individually below its limit. The combined contribution from all significant simultaneous sources must be assessed.

Induced and contact currents

Induced current is current flowing through a foot to ground in a free-standing person exposed to an electric field. Contact current is current through the body resulting from touching a conductive object charged or energised by an RF field. Both can cause perception, nerve stimulation, shocks, or burns even where an ambient-field result appears acceptable.

The Code provides controlled and uncontrolled reference levels for induced and contact currents from 3 kHz to 110 MHz, with instantaneous or six-minute averaging depending on frequency and mechanism. Work around large conductors, towers, fences, vehicles, guy wires, or other field-coupled objects may therefore require current assessment and contact-hazard controls in addition to measurement of ambient fields.

Exposure assessment

A complete assessment identifies whether the environment is controlled or uncontrolled and considers the source frequency, power, modulation, duty cycle, antenna characteristics, field region, accessibility, duration, spatial distribution, grounding, contact conditions, and simultaneous operation of other sources.

Measurements and calculations must use methods, instruments, calibration, and uncertainty treatment suited to the frequency and exposure geometry. Broadband instruments can support screening but may not identify individual contributors or distinguish stimulation- and heating-based requirements. Frequency-selective measurements or source-specific calculations may be needed where the result approaches a limit or several services are present.

Safety Code 6 sets the exposure criteria but does not establish a complete organisational RF safety program. Where controlled limits are used, the defining conditions require adequate field characterisation, awareness, understanding of risk, and practical ability to mitigate exposure. These requirements imply training, access control, documented operating conditions, suitable work practices, and reassessment following change.

Regulatory and practical use

The Code provides the health-based exposure limits underlying Canadian RF regulation, but the administrative and technical route to compliance is supplied by the responsible regulator. Equipment certification, base-station assessment, broadcasting, portable-device SAR, time-averaging algorithms, and other applications can be subject to separate federal procedures that adopt, interpret, or supplement Safety Code 6.

Provincial occupational-health requirements and organisational rules may also apply. A practitioner should therefore identify the jurisdiction, source type, affected population, and current regulatory document before selecting a measurement or calculation procedure. Compliance with one product test does not automatically establish compliance for every installation, accessory, operating mode, or workplace task.

Practical significance

Safety Code 6 is the central Canadian reference for RF human-exposure limits. Its main contributions are the controlled and uncontrolled environment definitions, the combination of internal-field and SAR basic restrictions with external reference levels, and detailed provisions for field strength, power density, induced current, contact current, multiple frequencies, and averaging.

For RF radiation safety, the Code supplies the exposure benchmark. Effective implementation requires competent assessment, correct classification of the environment, identification of all significant sources and tasks, suitable engineering and administrative controls, and use of the current regulatory procedures that give the health-based limits practical effect.