Egress & life safety (NFPA 101/72)

modified2026-07-21statusfinished

NFPA 101 Life Safety Code & NFPA 72 — occupant load, egress capacity, RSET/ASET margin, travel distance, and fire alarm circuit checks, in one reference.

Index

Occupant load estimator
Egress width capacity
RSET vs. ASET evacuation margin
Travel distance limit modification
Fire alarm battery capacity
NAC voltage drop
Ceiling height detector spacing reduction

Relation sets with a natural input-output curve include a Voici¹1Voici compiles a notebook to a static, serverless dashboard — mocked here as a static page, since this pipeline has no Jupyter kernel to run against. dashboard: a matplotlib-styled chart with the live input marked as a red point.

1.12 · Occupant load estimator

[1.12] Governing equation

$$\text{Occupants} = \left\lceil \frac{\text{Floor Area}}{\text{Occupant Load Factor}} \right\rceil$$

Occupant load factors per NFPA 101 Table 7.3.1.2 (representative values shown; verify against the current edition for your occupancy). Source: NFPA 101 Table 7.3.1.2, IBC Ch. 10.

Occupancy (load factor, ft²/person) Floor area (ft²)

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1.13 · Egress width capacity

[1.13] Governing equations

$$W_{\text{stair}} = N \times 0.3\ \text{in/person},\quad W_{\text{level}} = N \times 0.2\ \text{in/person}$$

$N$ occupant load served by the component. Source: NFPA 101 §7.3.3.

FIG. 01 — required clear width scales directly with occupant load N

Occupant load N Component type

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import numpy as np, matplotlib.pyplot as plt
N = np.linspace(0, 1000, 200)
W = N*factor
plt.plot(N, W); plt.scatter([N_input],[W_input], color='red', zorder=3)

FIG. 02 — required width W vs. occupant load N, current N marked in red

1.14 · RSET vs. ASET evacuation margin

[1.14] Governing equations

$$\text{RSET} = t_d + t_a + t_o + t_{\text{egress}},\quad \text{Margin} = \text{ASET} - \text{RSET} \ge 0$$

$t_d$ detection, $t_a$ alarm, $t_o$ pre-evacuation delay, $t_{egress}$ movement time. Source: SFPE Engineering Guide, ISO 13571.

FIG. 03 — safety margin is the gap between when hazard conditions become untenable (ASET) and when occupants clear (RSET)

Detection time td (s) Alarm time ta (s) Pre-evacuation delay to (s) Movement time tegress (s) ASET (s)

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1.15 · Travel distance limit modification

[1.15] Governing equation

$$D_{\text{max}} = D_{\text{base}} + \Delta D_{\text{sprinkler}}$$

Base travel distance limits are extended when the building is fully sprinklered per NFPA 13 (representative values shown; verify against the current NFPA 101 edition and occupancy chapter). Source: NFPA 101 Ch. 7.

Base travel distance limit (ft) Sprinkler status

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1.16 · Fire alarm battery capacity

[1.16] Governing equation

$$C_{\text{battery}} = 1.25 \times \left(I_{\text{standby}} \times 24\ \text{hrs} + I_{\text{alarm}} \times \frac{t_{\text{alarm}}}{60}\ \text{hrs}\right)$$

1.25 factor covers battery aging/derating. Source: NFPA 72 §10.6.

FIG. 04 — secondary battery sized for 24h standby plus a peak alarm period

Standby current (A) Alarm current (A) Alarm duration (min)

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import numpy as np, matplotlib.pyplot as plt
talarm = np.linspace(1, 15, 200)
C = 1.25*(Istandby*24 + Ialarm*(talarm/60))
plt.plot(talarm, C); plt.scatter([talarm_input],[C_input], color='red', zorder=3)

FIG. 05 — battery capacity C vs. alarm duration, current duration marked in red

1.17 · NAC voltage drop

[1.17] Governing equations

$$V_{\text{drop}} = 2\cdot I_{\text{total}}\cdot R_{\text{wire}}\cdot L,\quad V_{\text{EOL}} = V_{\text{source}} - V_{\text{drop}}$$

Notification appliances typically require ≥16 VDC at end-of-line. $R_{wire}$ in Ω/ft (copper). Source: NFPA 72, NEC (NFPA 70) Ch. 9.

Source voltage (V) Total current (A) Circuit length L (ft, one-way) Wire gauge (AWG, copper)

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import numpy as np, matplotlib.pyplot as plt
L = np.linspace(10, 500, 200)
Veol = Vsource - 2*I*R*L
plt.plot(L, Veol); plt.axhline(16, ls='--'); plt.scatter([L_input],[Veol_input], color='red', zorder=3)

FIG. 06 — end-of-line voltage vs. circuit length L, current L marked in red (dashed: 16V floor)

1.18 · Ceiling height detector spacing reduction

[1.18] Governing relation

$$S = S_0 \times f_{\text{height}}$$

$f_{height}$ is a de-rating factor applied above ~10 ft ceiling height (approximated here as a smooth linear reduction; consult NFPA 72 Table 17.6.3.1.1 for exact heat/smoke detector values). Source: NFPA 72 §17.6.

Base spacing S0 (ft) Ceiling height H (ft)

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import numpy as np, matplotlib.pyplot as plt
H = np.linspace(8, 50, 200)
S = S0 * f_height(H)
plt.plot(H, S); plt.scatter([H_input],[S_input], color='red', zorder=3)

FIG. 07 — adjusted spacing S vs. ceiling height H, current H marked in red