From 1999 to 2015, there were about 7,393 deaths from unintentional carbon monoxide (CO) poisoning in the United States. It’s often referred to as the silent killer – and for good reason. Since it's colorless and odorless, carbon monoxide is impossible to detect without a CO monitor.
Carbon monoxide is a well-known health risk in households but it's a topic that gets less attention in the workplace (see So, Your CO Detector Is Going Off to learn about CO risks at home). Workers who spend long amounts of time on loading docks are particularly vulnerable. They may be regularly exposed to fuel-powered truck exhaust fumes, and yet too few workplaces recognize this hazard and take appropriate steps to address it.
CO Exposure on the Loading Dock
A number of different factors affect emission concentrations and how much CO can travel inside a building:
- Number of vehicles in operation
- Size and efficiency of the engines
- Length of time they spend idling
- Driver technique
- Size and shape of the building
- Whether the building is open or closed up (for natural ventilation)
- Whether mechanical ventilation (like power exhaust fans) is operating
Exhaust emissions tend to be highest around the loading dock area, since more lift trucks run under full load in the dock than in other sections of the warehouse or facility.
So, how are workers exposed? You'll rarely see an open-air loading dock. Most loading docks are closed-in areas, which means they can trap the emissions from running trucks. Dock workers, moreover, might not take adequate protective measures because they may not even realize that they are being exposed to carbon monoxide.
Understanding the Risks
It doesn’t take much carbon monoxide to cause a fatal accident. But death isn’t the only risk that comes with CO exposure. Workers exposed to concentrations of the gas may experience:
Trucks that are not properly tuned and loading docks that are poorly ventilated increase the level of exposure. When both are combined, the excess – and often highly concentrated – carbon monoxide has no way to escape. The longer the truck idles, the more gas it emits, and the CO levels in the dock begin to rise.
OSHA caps the carbon monoxide exposure limit at 50 ppm over an 8-hour time-weighted average. This amount should not be exceeded even for a moment, and it’s best to keep exposure levels well below this limit.
Managing CO Hazards
There are three key approaches to controlling the risks associated with carbon monoxide in the loading dock.
Engine Control and Maintenance
Tuning lift trucks regularly is the best way to keep emission levels low.
The mechanic should use an electric CO meter, placing it in the lift truck's tailpipe to measure the emission level. Ideally, you want to aim for less than 1 percent (preferably 0.5 percent) CO being discharged.
Other methods for reducing carbon monoxide emissions include:
- Retrofitting with a catalytic muffler – this will help detect whether the engine air/fuel ratio is too rich or too learn, allowing for maximum efficiency and minimal harmful emissions
- Retrofitting with an air-to-fuel ratio controller – this can reduce CO (and NOx) emissions by up to 99.9 percent
- Using a fuel additive – an additive (like propane) improves engine combustion and fuel economy, and it may reduce CO emissions by 50 to 60 percent
Once trucks are tuned properly, it’s critical to look at building ventilation – or the lack of it.
An enclosed loading dock needs fresh outdoor air to release toxic exhaust, so there should be plenty of windows, doors, or other ventilation options. American Conference of Governmental Industrial Hygienist (ACGIH) guidelines recommend 5,000 cubic feet per minute of ventilation for every 60-horsepower propane engine that emits one percent of CO or less.
The building also requires an air exchanger to bring in fresh air and dilute the build-up of exhaust gases.
Most dampers and fans are located at ceiling peaks or on the roof, which doesn’t benefit the workers at ground level. To remedy this, consider placing exhaust fans at the same height as the inlet air opening and installing sheet metal ductwork to bring the air to floor level. It’s a good idea to offset the placement of the inlet and the exhaust, as this allows fresh air to more effectively disperse through the building.
The third strategy to manage CO exposure on the loading dock is to look at work practices and policies, awareness, and employee training.
Exposure Control Plan
Every workplace should have a written exposure control plan. To develop one, start by conducting an audit to identify the carbon monoxide hazards that are present in your loading dock. Discuss the results with supervisors and workers and generate solutions to help manage these hazards. For example, it might be a good idea to limit the number of lift trucks that can operate at one time.
Be sure to consider communication, as well. For example, you may post signs around the dock that:
- Identify carbon monoxide as a risk
- List the symptoms of CO poisoning
- Detail safe working procedures
Just like at home, it’s important to have fully operational carbon monoxide detectors at the loading docks. This will help warn workers if levels are getting too high.
Training and Awareness
Workers should also receive comprehensive training to increase awareness about this often-overlooked issue. Training could cover:
- Carbon monoxide hazards and their risks
- How loading dock workers are exposed to CO
- Steps to mitigate the risks
- CO poisoning symptoms and how to recognize a medical emergency
An informed workforce is a safer workforce, so taking the time to properly train workers and reinforce the knowledge is critical to preventing tragedy.
When we think of loading dock safety, we often think about dock-trailer separation, forklift safety, and safe loading and unloading practices. But carbon monoxide is a real threat to workers who spend their days around emission-producing trucks, and it’s an issue worth discussing.
Don’t wait until a fatal accident happens – consider where your workers are most at risk and take action now to minimize the concentration of CO in your loading dock area.
For all things Respiratory Protection, check out our Respiratory Protection Knowledge Center.