This is the body's capacity to withstand a fall.
Sf = md
Sf = impact force expressed in kN
m = mass of the user with his equipment,
d = deceleration expressed in G, corresponding to "n times" the acceleration
due to gravity at the Earth's surface: 9.81 m/s²
ime). For a given fall velocity, the time between the onset of braking and complete
stop determines the value of the deceleration, expressed in G.
The European standards
are based on studies which set the maximum acceptable deceleration at 6 G for
a worker at height. On the basis of a deceleration not exceeding 6 G, the impact
force experienced by the user depends on his weight: Sf = md
Petzl absorbers are designed to meet 6 G deceleration for the fall of a 100
kg user. The impact force transmitted to the body will not exceed the 6 kN standardized
value: Sf = 100*6*9.8 = 5.9 (6 kN).
The same deceleration for a 140 kg user generates a greater impact force: Sf
= 140*6*9.8 = 8.2 (8 kN). It is recognized that the body does not suffer injury
as the deceleration is less than or equal to 6 G. Petzl therefore allows that
an impact force of up to 8 kN is acceptable for a user of 140 kg (including
Similarly, we can accept an impact force Sf = 120*6*9.8 = 7.1 (7 kN)
for a user
of 120 kg (including equipment).
Sf for 100 kg and 6 G = 100 x 9.81 x 6 = 5,9
Sf for 120 kg
and 6 G = 120 x 9.81 x 6 = 7.1
Sf for 140 kg and 6 G = 140 x 9.81 x 6 = 8.2
In some situations, Petzl accepts that a user over 100 kg can undergo an impact
force greater than 6 kN, provided that the maximum deceleration is limited to