Basic Calculations for Occupational Safety and Environmental Health Professionals - Mathematics and Statistics for the Environment - page 407

15.5.7.1.3 Boyle's Law and Charles' Law Combined Problems
Problem: Calculate the volume of a gas at STP if 600 mL of the gas is collected at 25°C and 80
cmHg.
Solution:
New volume ( V 2 ) = 600 mL × (80 cmHg/76 cmHg) × (273 K/298 K) = 578 mL
Problem: If a gas occupies a volume of 100 mL at a pressure of 76 mmHg and 25°C, what volume
will the gas occupy at 900 mmHg and 40°C?
Solution:
New volume ( V 2 ) = 100 mL × (760 mmHg/900 mmHg) × (313 K/298 K) = 88.7 mL
Problem: If 500 mL of oxygen is collected at 20°C, and the atmospheric pressure is 725.0 mmHg,
what is the volume of the dry oxygen at STP?
Solution:
New volume ( V 2 ) = 500 mL × (725.0 mmHg/760 mmHg) × (273 K/293 K) = 443.5 mL
Problem: 2.50 g of a gas occupy 240 mL at 20°C and 740 Torr. What is the gram molecular weight
of the gas?
Solution:
240 mL × (273 K/293 K) × (740 Torr/760 Torr) = 217 mL
(2.50 g/217 mL) × (1000 mL/l L) × (22.4 L/1 mol) = 258 g/mol
15.6 VENTILATION
Simply put, ventilation is the classic method, and the most powerful tool of control used in safety
engineering, to control airborne environmental hazards. Experience has shown that the proper use
of ventilation as a control mechanism can ensure that the workplace air remains free of potentially
hazardous levels of airborne contaminants. In accomplishing this, ventilation works in two ways: (1)
by physically removing the contaminated air from the workplace, or (2) by diluting the workplace
atmospheric environment to a safe level by the addition of fresh air (Spellman, 2013). A ventilation
system is all very well and good (virtually essential, actually), but an improperly designed ventila-
tion system can make the hazard worse. This essential point cannot be overemphasized. At the heart
of an efficient ventilation system are proper design, proper maintenance, and proper monitoring.
The environmental professional plays a critical role in ensuring that installed ventilation systems
are operating at their optimum level.
Because of the importance of ventilation in the workplace, the environmental professional must
be well versed in the general concepts of ventilation, principles of air movement, and monitoring
practices. Environmental professionals responsible for indoor air quality must be properly prepared
(through training and experience) to evaluate existing systems and design new systems to control the
workplace environment. This section presents general principles of ventilation system design, evalu-
ation, and control and basic computations. This material should provide the basic concepts and prin-
ciples necessary for ensuring the proper operation of industrial ventilation systems. This material also
serves to refresh the knowledge of the practitioner in the field. Probably the best source of information
on ventilation is ACGIH's Industrial Ventilation: A Manual of Recommended Practice ; this text is a
must-have reference for every environmental professional responsible for ventilation systems.