Heat flux and burns; Overpressure and blast injuries; case studies
Heat Flux Hazards¶
Flames, hot metal surfaces, and other heat sources can cause burns. The heat flux is the amount of heat energy transferred per unit area per unit time. The heat flux is measured in W/m^2.
Figure 1:Industrial Hygiene Tools Image Reference
From Handbook of Chemical Hazards Analysis Procedures (1989), Table 4.2
| Heat Radiation Intensity (kW/m^2) | Time for pain (seconds) | Time for 2nd Degree Burn (seconds) |
|---|---|---|
| 1 | 115 | 663 |
| 2 | 45 | 187 |
| 3 | 27 | 92 |
| 4 | 18 | 57 |
| 5 | 13 | 40 |
| 6 | 11 | 30 |
| 8 | 7 | 20 |
| 10 | 5 | 14 |
| 12 | 4 | 11 |
You may have to click the ‘reference link’ twice to get it to work.
import pandas as pd
data = {'Radiation (kW/m2)':[1,2,3,4,5,6,8,10,12],
'Pain time (sec)':[115,45,27,18,13,11,7,5,4],
'2nd Degree Time (sec)':[663, 187,92,57,40,30,20,14,11]}
df = pd.DataFrame(data)DESR 6055.09 is the handbook for the Department of Defense and gives the following relationship for heat flux (q, kW/m2) and time,t, before a 2nd degree burn:
#Causitive variable from Probit correlations from death from burning
import numpy as np
time = np.linspace(5, 700, 1000)
def Q2(t):
return (t/200)**(-1/1.46)import matplotlib.pyplot as plt
df.plot(x='2nd Degree Time (sec)', y='Radiation (kW/m2)', kind = 'scatter', label='EPA 2nd Degree Burn')
plt.scatter(df['Pain time (sec)'], df['Radiation (kW/m2)'], marker = '+', label = 'EPA Pain threshold')
plt.plot(time, Q2(time), label = 'DESR 6055 Q')
plt.legend(); plt.show()
The above plot shows that the relationship used for the military (DESR 6055) is conservative relative to the EPA’s Handbook of Chemical Hazards Analysis Procedures. Considert that in full sun, the approximate radiation is 1 kW/m2. Would it really take 660 seconds (11 minutes) to get a sunburn that blisters? No, it would take longer indicating that both relationships are conservative.
200/603.3333333333333335Estimating thermal flux from a fire¶
The radiation from a fire or fireball descreases with the square of the distance from the fire. The heat flux is given by:
where is the power of the fire in watts and is the distance from the fire in meters.
Thus, if a fire has a power of 1 MW and you are 10 meters away, the heat flux is:
‘Your answer here’
How long would you have before a 2nd degree burn?
Overpressure Hazards¶
Noise¶
Sound pressure level (SPL) is used as an intensity measure. The lowest SPL that can be heard by the human ear is near 2E-5 Pa. Thus in the below equation is 2E-5 Pa.
where is the sound pressure and is the intensity.
See “Permissible Noise Exposures,” [https://
Industrial hygienists help protect workers from over exposure: Industrial Hygienists.