NASA-STD-3001 Technical Brief

Relevant Technical 

Requirements

Physiological Effects 

of Electrical Shock

OCHMO-TB-021

Rev B

NASA-STD-3001 Volume 2, Rev D

[V2 9017] Power Interruption

[V2 9018] Energized Status

[V2 9019] Nominal Physiological Electrical 

Current Limits

[V2 9020] Catastrophic Physiological 

Electrical Current Limits for all 

Circumstances

[V2 9021] Catastrophic Physiological 

Electrical Current Limits for Startle 

Reaction

[V2 9022] Body Impedance for Voltage 

Calculations Utilizing Electrical Current 

Thresholds

[V2 9023] Leakage Currents – Medical and 

Bioinstrumentation Equipment

Executive Summary

For spaceflight applications, it is important to 

protect humans from unintended electrical current 

flow. These technical requirements define the 

physiological limits for current flow for the following

situations:

• Nominal – Under allsituations

• Catastrophic – Hazard threshold for all conditions

• Catastrophic – Hazard threshold specifically for

Startle Reaction

• Leakage Current – Designed for Human Contact.

Current thresholds were chosen (vs. voltage 

thresholds) because body impedance varies 

depending on conditions such as wet/dry, AC/DC, 

voltage level, and large/small contact area; however, 

current thresholds and physiological effects do not 

change. By addressing electrical thresholds, 

engineering teams can provide the appropriate 

hazard controls, usually through additional isolation 

(beyond the body’s impedance), current limiters, 

and/or modifying the voltage levels. “Catastrophic 

hazard” language is used to relate the physiological 

level that shall not be exceeded without additional 

controls.

Body Impedance: Guidance is provided to 

determine the appropriate body impedance for 

calculating the associated voltage with a given 

current threshold.

Using blood pressure monitor on ISS

Source: NASA
NASA-STD-3001 Technical Brief

OCHMO-TB-021 Physiological Effects of Electrical Shock

NASA Office of the Chief Health & Medical Officer (OCHMO)

This Technical Brief is derived from NASA-STD-3001 and is for reference only.

It does not supersede or waive existing Agency, Program, or Contract requirements.

Background

Below is a summary of the electrical current thresholds:

11/30/2023

Rev B 2

Nominal

Perception

Current

Thresholds

[V2 9019]

Leakage Currents –

Equipment

Designed for

Human Contact

[V2 9023]

Catastrophic

Physiological

Startle Reaction

Current

[V2 9021]

Catastrophic

Physiological

Threshold Current

For all situations

[V2 9020]

DC Limits 0.4 mA Refer to Table

below

2.0 mA 40 mA

AC Limits 0.2 mA 0.5 mA 8 mA

AC = alternating current; DC = direct current ; mA = milliampere

Some equipment needs to pass small amounts of current through the body to accomplish its intended

function, e.g., bias currents in medical monitoring equipment. The amount of current allowed depends on 

the frequency and whether the part of the equipment contacting the crewmember is isolated from the 

power source. Examples of isolated equipment are intra-aortic catheters and electrocardiogram (ECG) 

monitors. Examples of non-isolated equipment are blood pressure cuffs and digital thermometers. These 

levels of leakage current are consistent with those in International Electrotechnical Commission (IEC) 60601-1, 

Medical Electrical Equipment – Part 1: General Requirements for Basic Safety and Essential Performance, for 

patient auxiliary and patient leakage currents in isolated (type CF – electrically connected to the heart) and 

non-isolated (types B and BF – no electrical contact; electronically connected but not to the heart)

equipment. These leakage currents are measured across parts applied to the crewmember and from parts

applied toground.

From: NASA-STD-3001 Volume 2 Rev D [V2 9023]
NASA-STD-3001 Technical Brief

OCHMO-TB-021 Physiological Effects of Electrical Shock

NASA Office of the Chief Health & Medical Officer (OCHMO)

This Technical Brief is derived from NASA-STD-3001 and is for reference only.

It does not supersede or waive existing Agency, Program, or Contract requirements.

Physiological Current Limits

Data/evidence to determine the physiological thresholds are from IEC documents along with associated 

rationale as follows:

Nominal – Under All Situations 

These values are below the physiological effect of sensation for the most sensitive members of the 

astronaut population. This requirement is intended to address typical exposure situations where human 

contact can routinely occur with conductive housing of electrical equipment. In these situations, no 

perceptible current flow is the design requirement. Typically, NASA engineering teams establish 1 MΩ 

isolation along with grounding to conductive surfaces with Class H or better bond to prevent current flow 

through crewmembers

Catastrophic Hazard Threshold 

These thresholds are used when a hazard analysis is considering failure scenarios and off nominal events 

where failures such as electrical short circuits have compromised system isolation and pose a risk of 

catastrophic electrical shock to the human:

• Catastrophic hazard threshold for all conditions - These current values were chosen based on the 

threshold for maintaining muscle control if shocked to protect 99.5% of the population (IEC TR 60479-2, 

Figure 7). This requirement is intended to provide the threshold where additional engineering controls 

will be required to mitigate electrical shock/physiological effects to the human.

• Catastrophic hazard threshold specifically for Startle Reaction - These current values were chosen 

based on the threshold for a startle reaction if shocked (IEC TR 60479- 5, Table 1). Under certain 

circumstances such as startle reaction, more restrictive thresholds than the physiological catastrophic 

limits of NASA-STD-3001 Volume 2 Rev D [V2 9020].

Leakage Current Designed for Human Contact 

These levels of leakage current are consistent with those in IEC 60601-1, Medical Electrical Equipment–

Part 1 (see table on previous page)

Body Impedance Guidance

In order to determine appropriate voltage levels not to exceed the current thresholds, the following 

guidance is provided: 

Utilize 5th percentile values for the appropriate conditions (wet/dry, AC/DC, voltage level, 

large/small contact area) from IEC TR6049-1 to determine the appropriate body impedance to 

calculate the voltage associated with any current limit analysis.

Background

11/30/2023

Rev B 3
NASA-STD-3001 Technical Brief

OCHMO-TB-021 Physiological Effects of Electrical Shock

NASA Office of the Chief Health & Medical Officer (OCHMO)

This Technical Brief is derived from NASA-STD-3001 and is for reference only.

It does not supersede or waive existing Agency, Program, or Contract requirements.

Data From IEC documents were utilized to set current thresholds:

Reference Data

11/30/2023

Rev B 4

[V2 9020] Catastrophic Hazard Threshold for All

Conditions The program shall limit the electrical 

current through the crewmember to ≤ (less than 

or equal to) 40mA for DC and ≤ (less than or 

equal to) 8 mA peak for AC to avoid catastrophic 

physiological effects to the crewmember. From: 

NASA-STD-3001 Volume 2 Rev D

The current values were chosen based on the

threshold for maintaining muscle control if

shocked to protect 99.5% of the population (IEC 

TR 60479-2, Figure 7). The DC component is the 

x-axis (red arrow), and the peak AC component is 

the y-axis (yellow arrow). The 99.5th percentile 

for the most sensitive population (women) was 

chosen.

[V2 9021] Catastrophic Physiological 

Electrical Current Limits for Startle 

Reaction During critical operations 

where a startle reaction is possible, the 

program shall limit electrical current 

through the crewmember to ≤ (less than 

or equal to) 2 mA for DC and ≤ (less 

than or equal to) 0.5 mA for AC to avoid 

potentially catastrophic conditions.

From: NASA-STD-3001 Volume 2 Rev D

Startle Response is defined as a current 

level flowing through the body that is 

just enough to cause involuntary 

muscular contraction. The current 

values were chosen based on the 

threshold for a startle reaction if 

shocked (IEC TR 60479-5, Table 1).
NASA-STD-3001 Technical Brief

OCHMO-TB-021 Physiological Effects of Electrical Shock

NASA Office of the Chief Health & Medical Officer (OCHMO)

This Technical Brief is derived from NASA-STD-3001 and is for reference only.

It does not supersede or waive existing Agency, Program, or Contract requirements.

Application

Standard Utilization Guidance

The electrical shock technical requirements were written to: (1) Provide parent technical requirement(s) 

for engineering requirement(s) to limit current flow in routine operations; NASA-STD-3001 Volume 2 Rev 

D [V2 9019 and V2 9026]; and (2) Provide information for use in determining severity of hazards in all 

failure/off-nominal situations; NASA-STD-3001 Volume 2 Rev D [V2 9020]; and for unique situations such 

as protecting for a startle reaction; NASA-STD-3001 Volume 2 Rev D [V2 9021].

11/30/2023

Rev B 5

[V2 9019] is the parent technical 

requirement that ensures

adequate isolation is maintained 

through the vehicle/operations for 

routine ops

Catastrophic Physiological Electrical

Current Limits [V2 9020] is thelimit

that shall not be exceeded underall

failure/off-nominal conditions

Nominal

Operations

Hazard Analysis

[V2 9023] is the parent technical 

requirement that ensures adequate 

isolation fordevices in contact with 

the humanbody

Catastrophic Physiological Electrical

Current Limits for Startle Reaction[V2

9020] is a lower limit that shall be

used for unique situations where a

startle reaction may be catastrophic

Body Impedance Guidance

In many instances, application of these technical requirements will require the determination of the 

appropriate body impedance for the calculation of voltage. NASA-STD-3001 Volume 2 Rev D [V2 9022] 

requires that the 5th percentile is selected in order to protect 95% of thepopulation.

To calculate the appropriate voltage not to

exceed the electrical thresholds, the proper

body impedance must be selected. Factors

that must be considered are the condition of

the human/environment (wet vs. dry), AC/DC,

voltage level, and large/small contact area.

An example utilizing IEC TR 60479-1, Table 3,

850 W represents the 5th percentile of the

population for a touch voltage of 125 volts

and a large contact area (such as full hand or

a surface area of 82 cm2) in saltwater-wet

conditions. (Note: Table 10 of IEC 607479-1

may be used for dry conditions). For a

catastrophic hazard analysis, NASA-STD-3001

Volume 2 Rev D [V2 9020], the maximum

voltage would be:

VDC threshold = 850 W x 40 ma = 34 VDC
NASA-STD-3001 Technical Brief

OCHMO-TB-021 Physiological Effects of Electrical Shock

NASA Office of the Chief Health & Medical Officer (OCHMO)

This Technical Brief is derived from NASA-STD-3001 and is for reference only.

It does not supersede or waive existing Agency, Program, or Contract requirements.

Back-Up

11/30/2023

Rev B 6
NASA-STD-3001 Technical Brief

OCHMO-TB-021 Physiological Effects of Electrical Shock

NASA Office of the Chief Health & Medical Officer (OCHMO)

This Technical Brief is derived from NASA-STD-3001 and is for reference only.

It does not supersede or waive existing Agency, Program, or Contract requirements.

Rev A  Rev B

• Updated information to be consistent with NASA-STD-3001

Volume 1 Rev B and Volume 2 Rev C.

Original  Rev A

• Updated information to be consistent with NASA-STD-3001

Volume 1 Rev B and Volume 2 Rev C.

Major Changes Between Revisions

11/30/2023

Rev B 7
NASA-STD-3001 Technical Brief

OCHMO-TB-021 Physiological Effects of Electrical Shock

NASA Office of the Chief Health & Medical Officer (OCHMO)

This Technical Brief is derived from NASA-STD-3001 and is for reference only.

It does not supersede or waive existing Agency, Program, or Contract requirements.

NASA-STD-3001 Volume 2 Revision D

[V2 9017] Power Interruption The system shall provide the crew with capability to control the 

power to an electrical circuit.

[V2 9018] Energized Status The system shall provide and display the de-energized status 

(interruption of electrical power) of a circuit to the crew and within their fields of regard.

[V2 9019] Nominal Physiological Electrical Current Limits Under nominal situations (routine 

human contacts to conductive housing), the program shall limit electrical current throughthe

crewmember to ≤ (less than or equal to) 0.4 mA for Direct Current (DC) and ≤ (less than or equalto)

0.2 mA peak for Alternating Current(AC).

[V2 9020] Catastrophic Physiological Electrical Current Limits for all Circumstances The program 

shall limit the electrical current through the crewmember to ≤ (less than or equal to) 40mA for DC 

and ≤ (less than or equal to) 8 mA peak for AC to avoid catastrophic physiological effects to the 

crewmember.

[V2 9021] Catastrophic Physiological Electrical Current Limits for Startle Reaction During critical 

operations where a startle reaction is possible, the program shall limit electrical current through 

the crewmember to ≤ (less than or equal to) 2 mA for DC and ≤ (less than or equal to) 0.5 mA for 

AC to avoid potentially catastrophic conditions.

[V2 9022] Body Impedance for Voltage Calculations Utilizing Electrical Current Thresholds The 

program/project shall use the 5th percentile values for the appropriate conditions (wet/dry, AC/DC, 

voltage level, large/small contact area) from IEC 60479-1, Effects of current on human beings and 

livestock - Part 1: General Aspects, to determine the appropriate body impedance to calculate the 

voltage associated with any current limit analysis.

[V2 9023] Leakage Currents – Medical and Bioinstrumentation Equipment For equipment such as 

bioinstrumentation and medical devices, that are specifically designed to contact the human body, 

electrical leakage currents caused by contact with exposed surfaces (including worst-case fault 

scenarios) shall be kept below the levels specified in Table 9.3-11—Leakage Currents-Medical and 

Bioinstrumentation.

Referenced Technical Requirements

11/30/2023

Rev B 8

View the current versions of NASA-STD3001 Volume 1 & Volume 2 on the 

OCHMO Standards website
NASA-STD-3001 Technical Brief

OCHMO-TB-021 Physiological Effects of Electrical Shock

NASA Office of the Chief Health & Medical Officer (OCHMO)

This Technical Brief is derived from NASA-STD-3001 and is for reference only.

It does not supersede or waive existing Agency, Program, or Contract requirements.

Reference List

1. Electrotechnical Commission (IEC) Documents https://standards.iteh.ai/

2. IEC TR 60479-1, Effects of current on human beings and livestock – Part 1: General aspects, 4th 

edition, 7/2007

3. IEC TR 60479-2, Effects of current on human beings and livestock – Part 2: Special aspects, 3rd edition, 

5/2007

4. IEC TR 60479-5, Effects of current on human beings and livestock – Part 5: Touch voltage threshold 

values for physiological effects, Edition 1.0, 11/2007

5. IEC 60601-1, Medical Electrical Equipment–Part 1, Edition 3.1, 10/2013

11/30/2023

Rev B 9