Raising the bar

In accidents when vehicles buckle around passengers or buildings collapse, rescuing victims often depends on lifting bags: the rugged rubber squares firefighters work into tight spaces and then inflate to lift debris or prize apart metal.

Trelleborg is a leading supplier of lifting bags, with its Sava branded bags accompanying firefighters called out to emergencies in more than 90 countries worldwide, from Tokyo, Japan to Houston, in the US, Sao Paulo, Brazil to Mumbai in India. Investment by Trelleborg has led to significant technical developments in the bags.

The 15-bar challenge

One of these was to increase the pressure of its lifting bags up to 15 bar. At the end of 2022, the Nova range of 15-bar lifting bags and the Vega range of 12-bar bags were certified and offered to customers, allowing fire services to lift heavier weights with a smaller bag. Engineering the largest bag in the range, the Nova 100, a square with sides of 84 centimeters that can lift an impressive one hundred metric tons, was a challenge.
 
“For the smaller bags, it's not a huge problem to make them 15 bar,” explains Anze Vidic, Director of R&D for lifting bags. “The issue comes when you're dealing with the top three or four sizes, which lift 50 to 100 metric tons, as it's very difficult to get the layers in the construction right so that they can hold the pressure.

Every bar counts

For rescue services and those whose lives they seek to save, the difference in lifting capacity can make all the difference: a 15-bar bag can lift a weight 25 percent heavier than a similarly sized 12-bar bag, and 87 percent more than an 8-bar bag.
 
Vidic, who comes from a family of firefighters and still volunteers for his local squad, cites a recent training exercise in which firefighters lifted a heavy municipal waste container using 8- and 12-bar bags. “With the 12-bar bag we were able to go a few centimeters higher and if you have a person trapped, a few centimeters can be the difference between life and death”.
 
It is not just the height: a bag with higher pressure capacity can lift an obstacle more rapidly.
 
“In a critical situation, that half a minute can matter,” Vidic highlights. “In 80 percent of situations, there’s no difference, but for special situations, the 15-bar bag allows a quicker rescue.”
 
The end user can either have lighter, smaller bags with the same performance, or the same size bags with better performance.
 

Meeting safety criteria

Safety was paramount when pushing the limits of the pressure the bags can withstand and the Nova is CE marked, being fully compliant with the European Union’s EN13731 certification. This is mandated by all fire services in the European Union and most fire services worldwide. The bag also fulfils all requirements of the American NFPA 1936 standard and Polish CNBOP certification.
 
To qualify, the bags had to sustain pressure four times higher than their design pressure without bursting, meaning they were inflated in tests to 60 bar.
 
“This pressure would never be allowed by a lifting bag’s controller,” explains Vidic.
 
The controller, which controls the pressure as the bags are inflated, has a safety valve that prevents inflation beyond 18-bar. It also has a deadman function, which stops inflating the bag if the lever is not actively pushed.
 
In addition, the bag needs to pass a puncture test, where it is pierced with a 2 centimeter long 6-millimeter-wide pin and inflated without losing any air. This is possible because the internal rubber bladder deforms to make way for the pin.

Innovations gain acceptance

Though most municipalities still choose to upgrade 8-bar bags to 12-bar bags, the demand for 15-bar bags is growing.
 
“Firefighters in general want to stick to tried and tested solutions so penetrating the market with such innovations takes time until trust is built and the products become widely accepted,” Vidic says.
 
“But our engineering and sales team support our distributers as instructors to help demonstrate the advantages of the 15-bar lifting bags to end users,” he adds. “Once the benefits are accepted, we have an advantage, because we are the ones who can offer such a product."
 
This is why Trelleborg hopes its high-pressure bag will pay increasing dividends over the next few years.
 
Vidic is skeptical over whether it will be possible to increase lifting bag pressures for larger bags beyond 15-bar, at least for bags reliant on aramid cords: “Until a stronger material than Kevlar is invented, we don't see much possibility.”