Once you have measured the air flow you will want to see what the original design specification for your paint booth airflow was.
Spray booth air flow requirements.
The three main styles of paint booths are cross draft down draft and side down draft paint booths.
Spray areas appear to be covered under 29 cfr 1910 107 which does not specify a minimum design airflow rate.
Spray booth safety tips.
Typical paint booth air flow values can be read about here or just remember typically a cross draft paint booth will have air flow of about 100 feet per minute based on the width and height of the booth a downdraft will have air flow of about 50 feet per minute.
Osha 29 1910 and nfpa 33 have minimum requirements for air flow to decrease the concentration of flammable materials in a spray paint booth.
The old standard was 100 linear feet per minute lfm and this is still stated in the international fire code ifc.
A critical step in selecting a spray booth system is establishing the minimum air velocity and volume requirements.
One hundred feet per minute is the guideline for air movement in the booth area.
Using the example from above 80 square feet multiplied by 100 feet per minute equals 8 000 cfm.
Controlling the paint booth air flow going into the booth with relation to the air being exhausted from the booth is critically important to maintain the proper flow of air over the item being painted and remove the over spray effectively.
Aside from these minimum requirements for paint booths there are some essential safety practices to make sure your booth is maintained properly.
Velocity and air flow requirements.
Restrict access for anyone with asthma allergies and respiratory illnesses.
Spray painting performed in the hangars will be primarily spot maintenance but large areas of the aircraft could occasionally be painted.
1910 94 c 6 i except where a spray booth has an adequate air replacement system the velocity of air into all openings of a spray booth shall be not less than that specified in table g 10 for the operating conditions specified.
The spray booth should be located to allow for proper air entry and flow through the booth.
Multiply the booth s face area by 100 feet per minute to achieve cfm.
This is the size of the fan needed.
Their air flow requirements are summarized below.
From your question is it not clear what you mean by semi downdraft booth.
In the past nfpa dictated paint booth air flow needed to be 100 fpm for non electric static coating application downdrafts were usually between 50 100 fpm.
We consider the painting area a spray area rather than a spray room or booth.
Some booths are designed so that air entering at the back of the booth but from the ceiling moves to the far end of the booth where exhaust filters are.