Basic Calculations for Occupational Safety and Environmental Health Professionals - Mathematics and Statistics for the Environment - page 420

15.6.5.6.3 Fan Total Pressure
The fan total pressure (FTP) represents all energy requirements for moving air through the ventila-
tion system. FTP is calculated by adding the absolute values of the average total pressures found at
the fan. If the sign convention is followed, then a formula for FTP is
FTP = TP out - TP in
Substituting for TP = SP + VP gives
FTP = SP out + VP out - SP in - VP in
If VP out equals VP in (i.e., if the average inlet and outlet velocities are equal), then the VP terms in the
above equation cancel, leaving
FTP = SP out - SP in
The FTP is often referred to as the fan total static pressure drop .
■ EXAMPLE 15.13
Problem: The outlet and inlet conditions at a fan are SP out = 0.10 in. and SP in = -0.75 in. What is
the FTP?
Solution:
FTP = SP out - SP in = 0.10 in. wg - (-0.75 in. wg) = 0.85 in. wg
15.7 NOISE
High noise levels in the workplace are a hazard to employees. High noise levels are a physical
stressor that may produce psychological effects by annoying, startling, or disrupting the worker's
concentration, which can lead to accidents. High levels can also result in damage to worker's hear-
ing, resulting in hearing loss. In this section, we discuss the basics of noise, including those elements
environmental practitioners responsible for worker safety need to know to ensure that their organi-
zation's hearing conservation program is in compliance with OSHA.
15.7.1 d eFinitions
There are many specialized terms used to express concepts in noise, noise control, and hearing loss
prevention. Environmental engineering practitioners responsible for ensuring proper engineering
design to reduce workplace noise levels and the in-house safety engineers responsible for compli-
ance with OSHA's Hearing Conservation Program requirements must be familiar with these terms.
The NIOSH (2005) definitions below were written in as non-technical a fashion as possible.
Acoustic trauma —A single incident which produces an abrupt hearing loss. Welding sparks
(to the eardrum), blows to the head, and blast noise are examples of events capable of pro-
viding acoustic trauma.
Action level —The sound level which when reached or exceeded necessitates implementation
of activities to reduce the risk of noise-induce hearing loss. OSHA currently uses an 8-hour
time weighted average of 85 dBA as the criterion for implementing an effective hearing
conservation program.