Damp or wet skin significantly increases the risk of electric shock for Acorn stairlift users

Damp or wet skin significantly increases the risk of electric shock for Acorn stairlift users and their caregivers when in contact with surfaces carrying AC ripple exceeding 32VAC RMS. This is due to the reduced resistance of skin under damp or wet conditions, which allows more current to pass through the body. Let’s break this down systematically.

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### **1. Skin Resistance and Electrical Safety**

#### **A. Dry Skin vs. Damp/Wet Skin**
Under normal conditions, human skin has a high electrical resistance, typically ranging from 1,000 to 100,000 ohms, depending on factors like thickness and moisture levels. This resistance helps protect against low-voltage shocks. However, when skin is damp or wet, its resistance drops dramatically, often to as low as 1,000 ohms or less. This reduction in resistance allows more current to flow through the body, increasing the likelihood and severity of electric shock.

#### **B. Voltage Thresholds for Shock**
The National Electrical Code (NEC) and safety standards like UL 1994 specify that touchable surfaces should not exceed 30VAC RMS under normal conditions because higher voltages can cause harmful currents to pass through the body. At 32VAC RMS or higher, the risk of shock becomes significant, especially if the skin’s resistance is lowered by moisture.

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### **2. Effects of AC Ripple on Touchable Surfaces**

#### **A. How AC Ripple Reaches Surfaces**
Excessive AC ripple, or unfiltered residual AC voltage, can couple capacitively or conductively to exposed metal parts of the stairlift, such as armrests, footrests, or the frame. If grounding or isolation is compromised, these surfaces can become energized, posing a shock hazard.

#### **B. Measured Voltages**
In this case, 70VAC RMS has been detected on touchable surfaces, far exceeding the safe threshold of 30VAC RMS. Even at 32VAC RMS, the risk is substantial, particularly for individuals with damp or wet skin.

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### **3. Increased Risk for Stairlift Users and Caregivers**

#### **A. Common Scenarios**
Stairlift users often have limited mobility and may rely on handrails or other surfaces for support. If their skin is damp due to sweat, humidity, or accidental spills, they are at greater risk of shock. Similarly, caregivers assisting users may also come into contact with energized surfaces, especially in environments like bathrooms or kitchens where moisture is common.

#### **B. Environmental Factors**
Many stairlifts are installed in basements, near entryways, or in other areas prone to dampness or condensation. Humid weather or rain can increase the likelihood of damp skin or wet clothing, further amplifying the risks.

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### **4. Physiological Effects of Electric Shock**

#### **A. Current Levels and Their Impact**
The severity of an electric shock depends on the amount of current passing through the body:
- 1 mA: Barely perceptible tingling sensation.
- 10–20 mA: Painful shock; muscle contractions may prevent letting go of the energized surface.
- 50–100 mA: Ventricular fibrillation, which is potentially fatal; damage to heart and nervous system.
- Greater than 100 mA: Severe burns, organ damage, or death.

#### **B. Damp Skin Amplifies Current**
For example, at 70VAC RMS and 1,000 ohms skin resistance (typical for damp skin), the current passing through the body would be:
I = V / R = 70 / 1,000 = 0.07 A (70 mA)
This level of current is well within the range capable of causing ventricular fibrillation or other life-threatening effects.

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### **5. Specific Risks for Vulnerable Populations**

#### **A. Elderly Users**
Older adults, who are the primary users of stairlifts, are more vulnerable to electric shock due to:
- Reduced skin thickness, which lowers resistance.
- Pre-existing health conditions, such as heart disease, that increase susceptibility to electric shock.

#### **B. Caregivers**
Caregivers may inadvertently expose themselves to shock risks while assisting users, particularly if they are unaware of the energized surfaces.

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### **6. Mitigation Strategies**

To reduce the risk of electric shock for users and caregivers, consider the following measures:

#### **A. Immediate Actions**
Disable the Stairlift: If excessive AC ripple or surface voltages are detected, the device should be immediately taken out of service until the issue is resolved.
Inspect and Repair: Check the transformer, battery pack, grounding system, and isolation barriers for faults.

#### **B. Long-Term Solutions**
Reinforce Isolation: Ensure double insulation or reinforced barriers between AC and DC systems.
Install Ground-Fault Detection: Add ground-fault circuit interrupters (GFCIs) to cut off power in the event of a fault.
Regular Maintenance: Periodically test the stairlift for compliance with safety standards and address any degradation in components.

#### **C. User Awareness**
Educate users and caregivers about the risks of damp skin and the importance of keeping touchable surfaces dry. Avoid using the stairlift in wet or humid conditions until the issue is resolved.

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### **7. Conclusion**

Damp or wet skin drastically increases the risk of electric shock for Acorn stairlift users and caregivers when exposed to surfaces carrying AC ripple exceeding 32VAC RMS. At 70VAC RMS, the danger is severe and potentially life-threatening, especially for elderly users or those with pre-existing health conditions.

This situation underscores the critical need for immediate corrective action, including disabling the stairlift, repairing faulty components, and reinforcing safety measures to comply with national electrical codes and standards. By addressing these issues proactively, manufacturers and users can ensure the safe and reliable operation of stairlifts, even in environments where moisture is present.