The National Institute for Occupational Safety and Health (NIOSH) released a fact sheet on odorant fade in natural gas and propane.
Odorant is a liquid added to natural gas and propane that releases a smell in case of a leak. The smell alerts anyone nearby about a leak since natural gas and propane are naturally odourless. The odorant is mercaptan, an organic sulphuric compound that releases a strong, distinctive smell. This odour can fade over time, however, through absorption or oxidation as the leaking gas runs through soil or concrete. Drywall, plywood and new piping storage tanks can also strip the odorant from natural gas and propane.
The NIOSH Fire Fighter Fatality Investigation and Prevention Program (FFFIPP) released their recommendations for firefighters responding to natural gas and propane incidents. Although NIOSH is a US-based organisation, the following recommendations for fire departments are applicable and effective around the world:
- Utilise gas detection equipment on all calls. Do not rely on sense of smell to determine if there is a leak of natural gas or propane.
- Understand that odorants from natural gas or propane can fade.
- Train on the proper calibration, maintenance and use of gas detection equipment to determine if a potentially explosive atmosphere is present.
- Recognise that a lack of odour can result from natural gas or propane contacting soil, concrete and a wide variety of building materials.
The fact sheet references an incident from September 2019 where a firefighter in Maine was killed and six others were injured when propane gas ignited at a newly renovated office building. NIOSH FFFIPP investigators identified odour fade as one of the key contributing factors in that tragedy.
In 2020, an explosion in Baltimore, Maryland killed two people and highlighted the need for fuel gas detection. These explosions and deaths are too common in the US, hence the importance of the fact sheet and public education push. In fact, the words ‘odorant fade’ are scarcely used across the US, even in public education initiatives. A 2017 Texas fire that involved odorant fade injured two men in a home and caused property damage. After that incident, the Railroad Commission of Texas, which regulates gas utilities in Texas, said that the terms odour fade and odour loss ‘are not found in state or federal pipeline safety rules, nor are these terms found in state or federal rules for public awareness/education requirements.’
In the UK, positive change seems to be occurring. Fatalities from gas pipelines have decreased in recent years from 1.4 per year in the years 1990–2012 to 0.4 per year from 2002 to 2012. The death totals are falling because the UK has been proactive in replacing iron main pipes with more durable piping.
Traditionally, the UK odorises coal, and reformed and natural gas when it is being transported. Natural gas is more apt to lose its odour faster than coal and reformed gas.
A 2015 study showed that if the UK moved to a carbon capture and storage (CCS) pipeline system for CO2 transport, odorisation could be implemented for low-pressure natural gas pipelines for public perception. The study, however, did not provide clear specifications for CO2 transported across Europe.
Safety issues surrounding natural gas and propane gas continue to arise, thus the reason that NFPA 715 Standard for the Installation of Fuel Gases Detection and Warning Equipment is currently in the early development phase. The proposed standard will cover the selection, design, application, installation, location, performance, inspection, testing and maintenance of fuel gas detection and warning equipment in buildings and structures.
In anticipation of that standard, the Fire Protection Research Foundation, the research affiliate of NFPA, recently released a report on combustible gas detection (CGD) placement. The research highlights the need for a gas detector in any room where a permanently installed fuel-gas appliance is placed, and underscored the following:
- Better performance was observed when the detector was placed closer to the leak source, there was an unobstructed path between the leak and the detector, and when the alarm threshold was lower.
- Alarm thresholds are measured in Lower Flammability Limit (LFL) – for example, a 10% LFL results in better performance than a 25% LFL.
- For natural gas detection, placing the alarm closer to the ceiling results in better performance. If a detector cannot be placed within six inches of the ceiling, it should be placed at least above the highest doorway opening.
- For liquefied petroleum gas, placing the alarm closer to the floor results in better performance.
- Additional detectors in rooms directly adjacent to where the gas-powered appliance is located can be useful as well. They reinforce safety measures in case the detector closest to the leak fails to go off. Extra detectors are also useful along staircases to upper and lower floors for alerting occupants about natural and liquefied petroleum gas, respectively.
The research looks to use modelling to justify requirements in NFPA 715 and to ensure that CGDs are in the best locations for early and accurate detection of leaks. The Research Foundation also hosted a webinar on the topic in March.
For more information on NIOSH odorant-fade recommendations for the fire service, check out the fact sheet at www.cdc.gov/niosh/docs/2021-106/pdfs/2021-106.pdf
For more information, go to www.nfpa.org
This article originally appeared, in part, on NFPA Today.
