OSHA MAD Presentation

Electric Power Generation,
Transmission, and Distribution
Electrical Protective
Equipment—
Minimum Approach Distances
MAD
§§1910.269(l)(3), (l)(4)(ii), (l)(5)(ii) & 1926.960(c)(1), (c)(2),
(d)(2)
How to comply
What is the minimum approach
distance for the worksite?
Voltage
TOV, if applicable
Meters or feet
What is the expected reach of the
employee?
Expected reach may not enter MAD.
§§1910.269(l)(3), (l)(4)(ii), (l)(5)(ii) & 1926.960(c)(1), (c)(2),
(d)(2)
What is the distance?
Employer must establish minimum approach
distances based on formulas in the standard.
For voltages up to 72.5 kV, the default distances
are the same as proposed.
For voltages exceeding 72.5 kV, the distances are
based on the equations used to calculate the
proposed distances (D = TOV × (C + a) + M).
§1910.269(l)(3) & Table R-3, & §1926.960(c)(1) & Table V-2
What is the distance?
Employer must establish minimum approach
distances based on formulas in the standard.
For voltages up to 72.5 kV, the default distances
are the same as proposed.
For voltages exceeding 72.5 kV, the distances are
based on the equations used to calculate the
proposed distances (D = TOV × (C + a) + M).
§1910.269(l)(3) & Table R-3, & §1926.960(c)(1) & Table V-2
MAD for ≤72.5 kV
(showing difference compared to existing §1910.269)
Voltage
(kV phase-tophase)
0.50 to 0.300
m
ft
Avoid contact
0.301 to 0.750
0.33 (+0.33)
1.09 (+1.09)
0.751 to 5.0
0.63 (-0.01)
2.07 (-0.01)
5.1 to 15.0
0.65 (+0.01)
2.14 (+0.06)
15.1 to 36.0
0.77 (+0.05)
2.53 (+0.20)
36.1 to 46.0
0.84 (+0.07)
2.76 (+0.18)
46.1 to 72.5
1.00 (+0.10)
3.29 (+0.29)
§1910.269(l)(3) & Table R-3, & §1926.960(c)(1) & Table V-2
MAD for >72.5 kV
MAD = 0.3048(C + a)VL-GTA + M
C = constant, 0.01 or 0.011, depending on exposure
a = saturation factor (per equations in Table R-3)
VL-G = phase-to-ground rms voltage, in kV
T = maximum anticipated per-unit transient overvoltage
(for phase-to-phase exposures, T = 1.35TL-G + 0.45)
A = altitude correction factor from Table R–5
M = 0.31 m (1.0 ft), the inadvertent movement factor
§1910.269(l)(3) & Table R-3, & §1926.960(c)(1) & Table V-2
Significant risk
OSHA determined significant risk for the standards
as a whole, not for individual provisions.
MAD is based on probability of 1/1000 of sparkover.
OSHA does not require accidents to demonstrate
significant risk.
See National Maritime Safety Ass’n v. OSHA, —
F.3d, 2011 WL 2417109 (D.C. Cir. 2011).
§1910.269(l)(3) & Table R-3, & §1926.960(c)(1) & Table V-2
Changes for Voltages
>72.5 kV
Maximum transient overvoltage (TOV)
Highest is 3.5 rather than 3.0.
Final rule anticipates that most employers will determine
maximum TOV.
Appendix B includes MAD tables for various values of
maximum TOV.
MAD for phase-to-phase exposures increases
substantially for voltages >350 kV because of error.
§1910.269(l)(3) & Table R-3, & §1926.960(c)(1) & Table V-2
Portable protective gap
Ground end
Line end
Don and doff rubber
gloves
Put on and take off rubber insulating gloves in a
position where the worker cannot reach into MAD.
§§1910.269(l)(4)(ii) & 1926.960(c)(2)(ii)
Unprotected workers
For work near live parts of >600 volts but ≤ 72.5 kV,
work from a position where the worker cannot reach
into MAD, except:
wearing rubber insulating gloves,
protected by insulating equipment,
using live-line tools, and
performing live-line barehand work.
§§1910.269(l)(5)(ii) & 1926.960(d)(2)