Electric shock: make it safe, then help — First Aid at Work Practice

Sample questions

1. 01HSE’s electricity FAQ says a person who contacts more than about 50 volts AC can be hurt directly or indirectly. Which of these is an indirect injury?

   • ATissue burned along the current’s path
   • BThe heart no longer beating properly
   • CBreathing stopped directly by the current itself
   • DA fall from a ladder after losing control

   Why: HSE says the direct harm comes through problems with breathing and the heart, while the indirect harm comes from losing control and falling from height or being caught by moving machinery. A fall from a ladder is the indirect injury. The heart and breathing effects are the direct ones HSE names.

2. 02A static jolt from a car door can exceed 10,000 volts, yet HSE says it does a person no harm. What explains this?

   • AIt lasts far too briefly to do harm
   • BVery high voltage only crosses the skin
   • CThe car’s tyres insulate the person
   • DStatic is DC, and DC cannot injure

   Why: HSE says a static shock can exceed 10,000 volts but lasts so briefly that it does no harm, which shows that how long the current flows is one of the things that decide how bad a shock is. HSE is clear that both AC and DC supplies can cause injury, so the DC answer is wrong. Mains current that keeps flowing is a different matter.

3. 03On a solar PV job, an apprentice says the DC side cannot hurt anyone because only AC can stop the heart. What does HSE say?

   • ADC only matters above the high-voltage threshold
   • BBoth AC and DC supplies can cause injury
   • CThey are right; DC passes harmlessly over the skin
   • DThey are right, unless the panels are wet with rain

   Why: HSE says both alternating and direct current supplies can cause injury, and that the effect on any one person is very hard to predict. HSE also names voltages as low as 50 volts between two parts of the body as able to stop the heart beating properly. Treat a shock from either kind of supply as serious.