SPF Ventilation Design for Interior 

Application in Existing Buildings*

Presentation by CPI/SPFA

Effective Workplace Practices/

HazCom Workgroup

*Including new buildings that cannot be completely vacated – for example commercial 

construction projects where workers are present in adjacent rooms or floors.
Objective and Overview

• Objective: Review status of exploration of dual fan 

vs. single fan ventilation approaches

• Presentation Overview:

– Ventilation 

– System Design and Operation

– Added Safety Considerations

– Discussion 

– Next Steps
Ventilation

• Importance of ventilation and containment 

– Basis for engineering controls strategy for safe application 

of SPF inside existing or occupied buildings

– Helps protect occupants and workers in adjacent areas 

from potential chemical exposure

• Benefits of ventilation

– In contained workspace, creates negative pressure

– In non-contained workspace (e.g., high volume 

warehouse), dissipates chemicals in air

– Reduce airborne levels of hazardous chemicals during and 

after application
Focus of Presentation

• Not all interior applications may need tandem 

containment/ventilation; ventilation alone 

may be sufficient in some applications

• The feasibility easibility of cont of containment/ventilation tilation 

should be considered in interior applications, 

however

• This presentation focuses on tandem 

containment/ventilation approaches
System Design Considerations

• Two-Part Design

(1) Containment

– Workspace must be nearly airtight

– Use plastic sheeting and tape

– Check with smoke pencil

(2) Active or Forced-air Ventilation

– Single fan exhausted to exterior OR

– Dual fan; exhaust + supply
System Design and Operation

• TBL Application is well defined; sizing, location and operation of dual-fan 

system fans is a ‘static’ process

– Fixed workspace (containment) volume and geometry

– Known application point = limited applicator range and movement

– Fixed fan locations to create fixed cross flow ventilation path

– Known containment leakage rate

inlet fan

exhaust fan Cross-flow 

ventilation

leakage, q negative pressure if qe > qi

e - qi

qe 

qi
System Design and Operation

• Interior SPF Application is NOT well defined...and not suited for dual-fan ventilation

1. Variable workspace volume and geometry at each jobsite

large commercial building

Every jobsite has a 

different size and shape

small residential attic

Multiple workspace 

geometries at each jobsite
System Design and Operation

• Interior SPF Application is NOT well defined...and not suited for dual-fan ventilation

1. Variable workspace volume and geometry at each jobsite

2. Moving application point - adaptable cross-flow ventilation needed

exhaust fan 

qe 

Very difficult to 

inlet fan

qi





Very difficult to 

control crossventilation without 

relocating fan(s)
System Design and Operation

• Interior SPF Application is NOT well defined...and not suited for dual-fan ventilation

1. Variable workspace volume and geometry at each jobsite

2. Moving application point - adaptable cross-flow ventilation needed

3. Leakage varies with each workspace

Leakage Rates...

• not always proportional 

to volume

Low leakage in large 

containment volume

to volume

• change as SPF is applied

Proper fan sizing and 

balancing is a challenge 

to maintain fixed 

ventilation rate

High leakage in small 

containment volume
exhaust fan 

qe 

System Design and Operation

• Interior SPF Application is NOT well defined...and not suited for dual-fan ventilation

1. Variable workspace volume and geometry at each jobsite

2. Moving application point - adaptable cross-flow ventilation needed

3. Leakage varies with each workspace

4. Fans can be improperly set up

Dual fan systems can positive pressure if qe < qi

inlet fan

qi

Dual fan systems can 

pressurize workspaces 

and force contaminated 

air OUTSIDE the 

containment workzone -

creating hazards for 

occupants and other 

workers if not balanced 

properly


Added Safety Hazards

• Trip Hazard Created

– Low light levels in many workspaces

– Limited visibility through supplied air respirators

– Limited body movement/control wearing PPE

– Cords and ducts from exhaust fans are trip hazard

– Tripping is especially dang ipping is especially dangerous in at ous in attics
Added Safety Hazards

• Emergency Egress Blocked

– Exhaust fan ducts through attic hatches, windows and 

doorways limit or prevent emergency egress

• Contamination Risk

– Foam and chemical droplets that accumulate on 

ventilation ductwork could be deposited in occupied 

spaces during transfer and relocation
EWP/HC Workgroup Approach

– Additional guidance can be provided to educate about 

workspace containment and negative pressure

– Dual-fan ventilation system will not be effective

• Will not provide sufficient or consistent crossventilation in workspace to eliminate use of SAR

• Too difficult to design, set up and operate in the field

• Creates additional worker safety issues that offset any 

reduction in air concentrations

Approach: develop and provide guidance on workspace 

containment plus single-fan ventilation strategy
EWP/HC Workgroup Approach

• Workspace Containment

– 4-6 mil PE (Visqueen) sheeting

– Overlap seams and seal with tape

– Proper hazard warning signs

– Test with smoke pencil or differential manometer
EWP/HC Workgroup Approach

• Single Fan Ventilation

– Use as exhaust fan ONLY

– Greatly reduces risk of fan imbalance or improper setup

– Negative pressure in workspace

• Validate with manometer or inward billowing of sheeting

– Size to deliver ~0.3-1.0 ACH minimum

• Negative workplace pressure generation only

• Not for contaminant level reduction

– Minimizes ducts and cords on floor of work area

– Minimizes blockage of emergency egress
EWP Workgroup Approach

Single-Fan 

Ventilation Concept

(negative pressure only)
EWP/HC Next Steps

• Get Agency feedback on single-fan ventilation concept

• Develop four-page guidance document for SPF applicators 

– Workspace containment 

– Single fan ventilation approach

– Consult ‘Br Consult ‘Breathe E eathe Easy’ document f document for formatting and presentation ormatting and presentation

• Seek EPA/NIOSH/OSHA input in February

• Disseminate guidance; integrate guidance into existing materials (update 

to reflect ventilation guidance)