Warning Light Radiation Shield — API 521

Tip & purge

Tip outside diameter [mm]

Tip exit above datum [mm]

Purge flow, total [Nm³/h]

Purge gas LHV [MJ/Nm³]

Heat release, entered directly [kW]

Set the purge flow to 0 to use the heat release field instead.

Flame

Flame length [m]

Flame droop below tip exit [mm]

Radiated heat fraction F [–]

Relative humidity [%]

The flame length comes from the API 521 correlation, computed separately and brought in here — the stack height tool on this site does it. The droop is practice, not standard: common rules give one or two tip diameters, capped at around 1.5 m.

Light & shield

Light, horizontal from stack axis [mm]

Light, height above datum [mm]

Shield edge, horizontal [mm]

Shield edge, height [mm]

Allowable radiation [kW/m²]

Shield position

Two points measured off the drawing, not a rule: the line of sight passes through the light and the edge of the shield. Any other construction would be an assumption invented here.

Within the allowable

0.85 kW/m²

269 Btu/hr/ft² against an allowable of 1.58 kW/m². The light sees 27% of the flame.

The dashed line is the line of sight from the light over the shield edge. The lit part of the flame is the part the light actually sees; the radiation is computed on that part alone, from its centre. Move the shield edge and watch the visible fraction change — that is the whole design decision.

Intermediate result	Value	Relation
Heat release	3,813 kW	Q = qv · LHV / 3.6
Flame end, horizontal reach	4,959 mm	√(L² − droop²)
Line of sight crosses flame axis at	3,628 mm	line intersection
Fraction of flame in view	0.268 –	clamped to 0 … 1
Centre of the viewed flame	4,294 / 3,074 mm (x / y)	midpoint of the visible part
Distance to the light	3.68 m	D = √(Δx² + Δy²)
Atmospheric transmissivity	0.941 –	τ = 0.79 · (100/RH)^(1/16) · (30.5/D)^(1/16)
Radiation on the light	0.848 kW/m²	K = τ · F · frazione · Q / (4πD²)
Radiation, imperial	269 Btu/hr/ft²	1 Btu/hr/ft² = 3.155 W/m²

What this does not cover

A two-dimensional section through one plane, with the flame as a straight line and a point source at its centre. It ignores wind, which moves the flame out of that plane and is the case that usually governs; it ignores reflected and re-radiated heat from the stack and the platform, convection from hot gas, and the flame from an actual relief event rather than the purge. The shield is treated as a straight edge. It is a screening calculation, not a verification, and carries no warranty.

Need the real study?

Send us the tip general arrangement and the platform layout and we will check the warning lights, the platforms and the access ways together, under wind, with the radiation contours behind them.