What is expected for sufficient ventilation in MRW fixed facilities?
In general, consolidation of MRW triggers the need for mechanical
ventilation. Examples of air contaminants that should be ventilated
include airborne dust from absorbents during lab packing and toxic and
flammable vapors during bulking operations. Compressed gas containers,
such as butane and propane bottles, may also need ventilation.
Whether consolidation of MRW takes place or not, consultation with the
Washington Department of Labor and Industries (L&I) and local fire
officials is necessary to determine the needs at a specific facility.
L&I gives guidance on controls that provide enough ventilation to
prevent worker exposure to hazardous substances. Fire officials provide
direction on fire and explosion prevention. L&I has confidential
available to employers at no cost.
Though you need to contact L&I and local fire officials, this document
provides some guidance. The only numeric measure in chapter 173-350 WAC
for MRW facilities states, “[f]lammable or explosive gases do not exceed
ten percent of the lower explosive limit in the area where MRW is
handled.” Adherence to L&I and local fire codes should prevent reaching
Bulking of Toxic or Flammable Substances
For facilities that bulk toxic and flammable substances (combining
oil-based paint, thinners, solvents into a drum; evacuation of spray paint
aerosol cans and propane containers), the following are L&I’s best management
practices to keep concentrations below
permissible exposure limits
Mechanical ventilation in areas where workers bulk materials.
Full enclosure of drums that are being bulked into.
Natural ventilation is unpredictable, both in direction and in airflow
volume. This makes it nearly impossible to set up reliable work
practices to minimize exposure. Mechanical ventilation and use of a hood
provides consistent airflow to keep harmful substances from employee
breathing zones and prevent an accumulation that could lead to fire or
L&I does not allow use of respirators instead of mechanical ventilation.
Respirators may be used to control worker exposure only when ventilation
is not feasible, when it does not lower the air contaminant levels below
their permissible exposure limits or in emergencies.
Also for areas where workers bulk flammables, section 7903.2.3.4.2 of
the 2000 Uniform Fire Code (there are newer versions) states that:
"[c]ontinuous mechanical ventilation shall be provided at a rate of not
less than 1 cubic foot per minute per square foot of floor area over the
design area. Provisions shall be made for introduction of makeup air in
such a manner to include all floor areas or pits where vapors can
collect. Local or spot ventilation shall be provided when needed to
prevent the accumulation of hazardous vapors."
Storage of Toxic or Flammable Substances
For ventilation of toxic or flammable liquid storage area, an L&I rule,
WAC 296-24-33009, states:
"Every inside storage room shall be provided with either a gravity or a
mechanical exhaust ventilation system. Such system shall be designed
to provide for a complete change of air within the room at least six
times per hour. If a mechanical exhaust system is used, it shall be
controlled by a switch located outside of the door. The ventilating
equipment and any lighting fixtures shall be operated by the same
switch. A pilot light shall be installed adjacent to the switch if Class
I flammable liquids are dispensed within the room. Where gravity
ventilation is provided, the fresh air intake, as well as the exhaust
outlet from the room, shall be on the exterior of the building in which
the room is located.”
There are two basic types of ventilation - area ventilation and local
exhaust (spot) ventilation. Area ventilation exchanges air in the
building or areas of a facility. Spot ventilation removes contaminants
at the point of generation, so is the most appropriate type in areas
where bulking occurs. It is also effective in removing dust particles.
Spot ventilation uses a fixed exhaust register or a movable,
articulated-arm ventilator (see image at left). Place the ventilator as
close as possible to the air contaminant source to remove the hazard.
Orient it to draw air away from the worker’s breathing zone and not
through the worker’s breathing zone.
A qualified ventilation engineer or firms specializing in this field and
L&I and local fire officials should approve ventilation design. See
ventilation guideline for some basics.
Summary of Standards
||Numeric performance or design standard
||Standard or citation
|Solid Waste Rule
||Less than 10 percent LEL for flammable vapors
WAC 173-350-360 (6)(a)(xi)
|Labor and Industries
||List of air contaminant concentration limits
|Labor and Industries
||More than six complete air changes per hour
|Uniform Fire Code
||One cubic foot of air per minute per square foot of design
||Section 7903.2.3.4.2 UFC
* Note: The answers provided to Frequently Asked Questions are guidance
for implementing WAC 173-350-360. Following this guidance is not a
requirement of operation or design for MRW facilities, as facilities may
meet regulatory requirements through other means. Local Health
Departments should be consulted to determine what will be sufficient to
meet the regulatory standards.