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MEMORANDUM

DATE: February 6, 2012

SUBJECT: Leaks Observed from Fixed Roof and Floating Roof Fittings

FROM: Nick Parsons, EPA

1.0 INTRODUCTION AND BACKGROUND

The purpose of this memorandum is to document significant leaks from fittings on fixed roof 

tank rooftops and floating roofs that have been detected by EPA inspectors using sensory means 

(visual, auditory, olfactory) and optical gas imaging (OGI) techniques.

EPA inspectors have conducted numerous OGI inspections of fittings on fixed and floating roofs 

where fittings have been found to be leaking. These leaks have been identified both from storage 

vessels that are subject to visual inspections as well as from storage vessels that are not currently 

subject to inspection requirements. In many cases, these vessels have been found to be leaking 

even when a visual inspection of the rooftop or floating roof fittings indicate that the gaskets, 

seals, and other elements of closure devices appear to be sound, and the conservation vent is not 

actively releasing to relieve increased pressure caused by diurnal temperature changes or filling 

of the storage vessel.

Images taken by EPA inspectors of leaking storage vessel rooftops can be found in section 2.0 of 

this memorandum. OGI videos taken by EPA inspectors of leaking storage vessel rooftops can 

be found in section 3.0 of this memorandum.

2.0 SUPPORTING IMAGES

Figures 1 and 2 show a leaking emergency relief valve on a fixed roof tank at a Midwestern 

chemical manufacturing facility. During a June 2009 inspection, an EPA inspector who was 

conducting an inspection of the facility decided to inspect the rooftop of a fixed roof tank, even 

though an inspection was not required. The inspector then discovered a very noticeable leak of 

stored material occurring from the emergency relief valve, a 75 lb gasketed relief device 

intended to release only in an absolute worst-case scenario. The facility informed the inspector 

that they were unaware that there was a leak present on the rooftop, as they had not previously 

conducted an inspection to look for such a leak.
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Figure 1. Leaking Emergency Relief Valve

Figure 2. Leaking Relief Blowout Valve (View of Seal)
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Figures 3 through 5 show a crude oil storage tank at an Alaskan refinery where inspectors used 

their visual and olfactory senses to find vapor loss from a tank. During the inspection in July 

2010, EPA inspectors climbed to the tank top to observe the access hatches. One of the hatches 

had a very noticeable petroleum odor, even though it was closed. Inspectors saw a visible 

accumulation of crude/tar around the edges of the hatch which was another indication of vapor 

loss. The hatch had a clasp which was not clipped to ensure a tight fit. Inspectors pointed out 

these problems and recommended the clamp be kept closed tight and also the installation of a 

gasket on the hatch to help prevent vapor loss.

Figure 3. Leaking Access Hatch (View of Rooftop)
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Figure 4. Leaking Access Hatch

Figure 5. Leaking Access Hatch (View of Clasp)
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3.0 SUPPORTING OPTICAL GAS IMAGING VIDEOS

Many EPA inspectors have begun to conduct a survey of a facility’s storage vessels using OGI 

cameras. The use of this technology is not currently required by any EPA regulation, but is 

generally used as a screening device by both the EPA and the facility to discover leaking 

components that need to repaired or replaced. Several videos were provided by EPA inspectors 

surveying various storage vessels at chemical manufacturing facilities and refineries. The leaks 

were all brought to the attention of the facility at the moment of observation, and several 

facilities have stated that they would look into purchasing an OGI camera in order to conduct 

inspections of their tanks the same way the EPA inspectors did.

None of the leaks observed had been detected using the currently required visual, sensory, or seal 

gap inspections for storage vessels, and these inspections are typically unable to assess the 

condition of the seal mechanism. For example, the rim seals on a floating roof are only 

considered failing if there is a gap of a certain width observed during a periodic test. Recent 

periodic tests conducted by the facilities in the videos showed that those storage vessel seals had 

an allowable gap and that there were no tears noted. However emissions were still observed with 

the camera, meaning there are emissions even though the seal gap measurements showed the seal 

to be in compliance with the existing standard. While there is no way to quantify the magnitude 

of the emissions using the camera with current technology, assuming zero emissions just because 

the tank passes a seal gap measurement test may not be accurate. These leaks are likely to go 

unrepaired, as the seals were in compliance based on the most recent seal gap measurements, 

which is the method the facility uses to determine compliance. Another example is the automatic 

bleeder vents on the floating roofs. Current regulations require that these vents be closed at all 

times except during times when the roof is landed on its leg supports. However, as seen in 

videos, there is no way to tell that these vents are not sealing correctly using visual methods 

without the use of an OGI camera.

Twelve videos are contained in the Confidential Addendum to this memorandum. Video 1 is an 

OGI video showing a leaking conservation vent/vacuum control off of a diesel storage tank at a 

refinery. Video 2 is an OGI video showing a leaking vacuum control from a fixed roof storage 

tank at a chemical manufacturing facility. Video 3 is an OGI video showing a leaking 

conservation vent/vacuum control from a fixed roof tank at a chemical manufacturing facility. 

Video 4 is an OGI video showing a leaking emergency relief valve on a fixed roof storage vessel 

at a chemical manufacturing facility. Video 5 is an OGI video showing a leaking bleeder vent 

from an external floating roof tank at a chemical manufacturing facility. Video 6 is an OGI video 

showing a leaking hatch/cover on a fixed roof tank. Videos 7 and 8 are OGI videos from the 

same external floating roof tank and show a leaking rim seal and a leaking automatic bleeder 

vent and rim seal, respectively. Videos 9 and 10 are OGI videos from the same floating roof tank 

and show leaks from the conservation vents on the side of the tank as well as a leak source from 

a vent on the top of the vessel, which indicates that there is a leak from the internal floating roof 

that is making it out through the fixed roof of the tank. Video 11 is an OGI video of a leaking 

hatch on an oil/water tank at a sour gas production plant that appears to be closed upon visual 

inspection. Video 12 is an OGI video of a leaking hatch on an oil/water tank at a sweet gas 

production plant that appears to be closed upon visual inspection.
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Docket EPA-HQ-OAR-2010-0871

The following information is located in the Confidential Business Information (CBI) Office, 

Office of Air Quality Planning and Standards, U.S. Environmental Protection Agency, Research 

Triangle Park, North Carolina 27711. This information is confidential pending final 

determination by the Administrator and is not available for public inspection.

Addendum to memorandum titled “Leaks Observed from Fixed Roof and Floating Roof Fittings” 

(CBI Item No. 12504-A15-01).

The addendum consists of 12 confidential optical gas imaging videos showing emissions from 

fittings on both fixed roofs and floating roofs and from rim seals on storage vessels equipped 

with external floating roofs.