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PD 06519 — Guide to Effects of Current on Human Beings and Livestock Standard Series (PD 6519)
Guide to Effects of Current on Human Beings and Livestock (Published Document series)
📐 PD 6519 is a British Standards Institution (BSI) “Published Document” (PD) series adopting the IEC 479 series (Effects of current on human beings and livestock), providing a systematic quantitative guide to the physiological effects of electric current passing through the human body and livestock. The series is an important basis for electrical safety design (electric-shock protection, earthing and protective devices). This batch collects two parts: Part 1 (PD 6519-1:1995, corresponding to IEC 479-1:1994) is general aspects, and Part 2 (PD 6519-2:1988, corresponding to IEC 479-2:1987) is special aspects relating to human beings.
💡 The core of electric-shock protection design is the “current-time-path” three dimensions. PD 6519 gives body impedance, perception/let-go/ventricular fibrillation thresholds and quantified data for different frequencies, waveforms and paths, providing a basis for selecting shock-protective devices.
1. Series Overview and Positioning 📌
PD 6519 is the responsibility of BSI electrotechnical committees (e.g. PEL/64, Electrical installations). Part 1 gives general basic data (body impedance, effects of a.c. 15-100 Hz, d.c. effects); Part 2 gives special effects at higher frequencies, special waveforms and short-duration impulse currents. Together they form the complete data foundation of the human electric-shock effect.
This batch contains the following two parts:
| Document | Subject | Edition | International source | Core content |
|---|---|---|---|---|
| PD 6519-1:1995 | Effects of current on human beings and livestock — Part 1: General aspects | 1995 | IEC 479-1:1994 | Body impedance, effects of a.c. 15-100 Hz and d.c., perception/let-go/ventricular fibrillation thresholds, current-time zones |
| PD 6519-2:1988 | Effects of current on human beings and livestock — Part 2: Special aspects relating to human beings | 1988 | IEC 479-2:1987 | Effects of a.c. above 100 Hz, special waveforms (d.c. component, phase control, multicycle control) and short-duration unidirectional impulse currents |
⚠️ Part 1 provides “general” basic data; Part 2 provides “special” (frequency, waveform, pulse) data. When assessing real shock risk, select the relevant part by current frequency, waveform and duration, not by a single threshold.
2. Body Impedance and Current-Time Zones (Part 1) 🔬
Part 1 first gives the body impedance model:
- Internal body impedance (Zi): impedance of body internal tissues, varying with current path.
- Skin impedance (Zp): skin contact impedance, varying with voltage, frequency, humidity and contact area.
- Total body impedance (ZT): the sum of skin and internal impedance, the basis for shock-current calculation.
- Initial resistance (R0): equivalent initial resistance at high frequency/high voltage.
The document gives statistical values of total body impedance under a.c. 50/60 Hz and d.c. (for hand-to-hand, hand-to-foot and other paths and contact areas), and the effect of contact area on impedance. These data are used to calculate the shock current for different contact voltages.
2.1 Current Effect Thresholds
The document defines key shock-effect thresholds and gives time/current zones:
- Perception and reaction threshold: the threshold at which a human can perceive the current and reacts involuntarily.
- Let-go threshold: the maximum current a human can voluntarily release; above it, muscle spasm prevents release.
- Ventricular fibrillation threshold: the threshold causing ventricular fibrillation (fatal arrhythmia), related to current duration, path and the heart-current factor (F).
The document describes time/current zones (e.g. AC-1 to AC-4) in a figure (Figure 14), providing a basis for the trip characteristics of protective devices.
3. Special Waveforms and Impulse Currents (Part 2) ⚡
Part 2 extends the analysis to more complex situations:
- Alternating current above 100 Hz: for 100 Hz-1 kHz, 1 kHz-10 kHz and >10 kHz bands, gives the variation of perception, let-go and ventricular fibrillation thresholds with frequency.
- Special waveforms: the effect of a.c. with d.c. components, phase-control waveforms (e.g. dimming) and multicycle-control waveforms (e.g. power control) on the ventricular fibrillation threshold.
- Short-duration unidirectional impulse currents: effects of rectangular impulses, sinusoidal impulses and capacitor discharges, with waveform figures and threshold curves.
These data are especially important for assessing shock risk from nonlinear and pulsed current sources such as variable-frequency drives, switch-mode power supplies and medical equipment.
💡 Engineering note: increasing frequency generally raises the perception and let-go thresholds (body impedance falls, nerve sensitivity changes), but the ventricular fibrillation risk remains; for high-frequency and pulsed currents, evaluate using Part 2 curves rather than 50/60 Hz data.
4. Engineering Practice Points ⚙️
- 🔍 Earthing and protection: set protective device (RCD, fuse, circuit breaker) trip characteristics by the shock current-time curve, ensuring supply is cut before ventricular fibrillation occurs.
- 🔧 Contact voltage limits: combine body impedance and permissible current to determine safe touch voltage and earthing system design parameters.
- 📊 Special equipment assessment: for variable-frequency, pulsed and d.c. systems, evaluate shock risk using Part 2 curves.
- 📋 Medical and special locations: in sensitive environments (hospitals, swimming pools, damp locations), adopt lower safe touch voltage and faster tripping.
5. Frequently Asked Questions ❓
❓ Q: Why must shock protection consider current duration?
A: The ventricular fibrillation threshold varies significantly with duration — the longer the time, the lower the permissible current. Protective devices must cut the current within the safe time, so design is based on the current-time curve.
A: The ventricular fibrillation threshold varies significantly with duration — the longer the time, the lower the permissible current. Protective devices must cut the current within the safe time, so design is based on the current-time curve.
❓ Q: What does the let-go threshold mean?
A: The let-go threshold is the maximum current a human can voluntarily release from a live conductor. Above it, muscle tetanic contraction prevents release, the shock persists, and risk rises sharply.
A: The let-go threshold is the maximum current a human can voluntarily release from a live conductor. Above it, muscle tetanic contraction prevents release, the shock persists, and risk rises sharply.
❓ Q: What is the role of the heart-current factor (F)?
A: Ventricular fibrillation risk depends on the proportion of current through the heart. The heart-current factor corrects for different current paths (e.g. hand-to-hand, hand-to-foot, foot-to-foot) to derive an equivalent heart current.
A: Ventricular fibrillation risk depends on the proportion of current through the heart. The heart-current factor corrects for different current paths (e.g. hand-to-hand, hand-to-foot, foot-to-foot) to derive an equivalent heart current.
🔍 Q: Is high-frequency current safer than mains frequency?
A: At high frequency the perception and let-go thresholds usually rise, but ventricular fibrillation risk is not eliminated and burns can occur. For high-frequency systems, still evaluate per Part 2 and take protection.
A: At high frequency the perception and let-go thresholds usually rise, but ventricular fibrillation risk is not eliminated and burns can occur. For high-frequency systems, still evaluate per Part 2 and take protection.