Part two of our series on firefighter safety at rescue

Published:  29 July, 2011

The UK Rescue Organisation writes on how to work around air suspension of large vehicles.

In the last edition we looked at ensuring the vehicles parking brakes were applied at the earliest stage negating the risk of vehicle movement.

The next consideration for attending crews working around a large goods vehicle or public service vehicle must be an appreciation of the vehicles suspension system and how to assess, work around it or utilise it safely.

Around 80% of the commercial vehicle traffic on the roads these days use air suspension, whether for passenger comfort on a large coach travelling into Europe or an articulated LGV delivering to a supermarket where the trailers height can be adjusted to assist with unloading.

The system offers numerous benefits to the owner/operator;

  • - Reduces occupant and vehicle fatigue
  • - Maintains a constant ride height regardless of load
  • - Fully adjustable
  • - Reduces the vehicles unladen weight
  • - Interfaces electronically with other vehicle systems

Systems fall into two main categories, vehicle/cab suspension or axle lifting suspension.

Both systems are supplied with compressed air from the vehicles compressor, this air is dried/ filtered (to remove water and other contaminants) and then stored for use in steel tanks at approximately 10 bar.

The air supply for the vehicles suspension systems comes from the auxiliary circuit.

It is supplied around the vehicles chassis via plastic pipe work and fittings, to numerous valves and controls blocks to ensure it is at the required pressure for the suspension air bag units depending on load.

This regulated air terminates at air bag units mounted between the chassis rail and the axle beam. Each wheel will have either a single or double bag fitted depending on application.

Air bag units are constructed of a reinforced neoprene rubber bag mounted over a steel cylinder (U Bellow type), increasing air supply to the bag will force the bag to expand lengthways forcing it away from the steel cylinder (increasing suspension travel), a reduction in supply pressure will cause the bag to deflate and form around the cylinder reducing its height.

These air bags take the place of the previous leaf spring type suspension systems which have been phased out over time.

Vehicles with lifting axles use separate air bags/s (folding bellows) in conjunction with a pivoting type framework to lift an axle off the road surface when it’s not required. This is done by deflating the main suspension air bags and inflating the lifting air bag/s simultaneously.

The purpose of these lifting axles is to reduce tyre and drive train wear along with improved fuel consumption, when the vehicle does not need the axle for load carrying, i.e. lightly loaded or empty.

In general, prime movers (Tractor units/ rigid vehicles) have electronically controlled air suspension on their main drive axle and where fitted middle lifting axle, whereas trailer air suspension is normally controlled by pneumatic valves.

The majority of front axles carry leaf spring suspension as they have no requirement for adjustment.

Modern PSV vehicles will be fully air suspended on all axles to give maximum passenger comfort and to allow ride heights to be lowered to assist passengers when boarding.

Air suspension systems are susceptible to damage from fire, impact, tyre blow out and general wear and tear.

For incident commanders and crews at these types of incident there are many considerations to ensure safety for all concerned.

  • - Has the vehicles air suspension system been damaged?
  • - Older/ poorly maintained vehicles will lose air over time with the engine off.
  • - Lifted axles are held off the road by air pressure only, there is no interlock fitted.
  • - Shutting off the engine may cause a lifted axle to drop.
  • - Electronically controlled systems will continue to adjust the suspension if left active.

In the early stages of an incident consideration should be given to leaving the engine running (if practicable) while the suspension is assessed/ made safe, this will ensure the vehicles ride height is maintained.

Any lifted axles can be lowered or if not practical then chained, strapped or blocked in the raised position.

Chassis stabilisation using LGV rated props or similar should be employed before committing personnel under an air suspended vehicle. (LGV trailer landing legs can be employed in this way, but crews need to ensure the rear of the trailer is also stabilised to ensure no rear suspension drop can occur)

For Fire Service personnel working around LGV/ PSV air suspension systems the main risk is the loss of air in the system.

This can happen over a period of time causing a trailer to slowly drop or possibly a lifted axle starts to fall. Its worth remembering air suspension units can fail without warning causing a potential load shift.

If managed properly these incidents are safe for all, but a good understanding and respect for the subject is fundamental.

For further information please visit the education section of the United Kingdom Rescue Organisation website UKRO.

  • Operation Florian

Sign up: eMagazine & eNewsletter

The latest issues in your inbox.

Company Profiles

Renka´s Fire Engine No. 1

Firefighting, fast, safe, everywhere. Michael Renka GmbH, based in Germany, is a manufacturer of firefighting vehicles, pumps and rescue equipment.

Waterax - We move water

Trusted by wildland firefighters around the world, WATERAX sets the industry standard by developing innovative, portable fire pumps and water-handling equipment designed to withstand demanding applications and rugged environments.

Big Water Flow for Industrial and Municipal Firefighting Applications

Protecting the lives of the public and firefighters while limiting the structural damage caused in large scale fires is our primary mission

We are committed to improving lives and doing business in the right way

We have a unique mix of capability and culture that we refer to as 3M Science and we strive to develop products that improve people’s daily lives in a multitude of ways.

HazSim - Bringing situational HazMat training to life

HazSim, LLC provides innovative simulation training to ensure your team works safely and effectively. HazSim Pro simulation equipment is in use by hundreds of fire departments, training schools, industrial fire teams, and private trainers across the US, Canada and further afield as well as the US Army.

The ultimate in innovation, quality and service

For 60 years Lehavot has been delivering the world’s most advanced fire detection and suppression automatic systems

Advancing rescue technology

The specialist supplier of quality PPE and Rescue Equipment to Emergency Services.

Revolutionizing fire fighting foam technology

The one-stop resource for fire fighting foam concentrates and custom-designed foam suppression systems hardware.

Trust the best, let us be your foam solution

AUXQUIMIA is a Spanish company whose main activity is the design, manufacture and commercialization of firefighting foam concentrates.

Williams Fire & Hazard Control offers a full line of specialized fire response equipment for oil and gas platforms

From storage tanks and pipeline emergencies to offshore platforms and vessels at sea, Williams' response personnel and specialized equipment quickly address adverse fire emergencies.

The leader in truck-mounted hydraulic platforms

Our mission is to provide the best and the safest solution to professionals that work at height.

If you want quality, you want Zico

Since its inception Ziamatic Corp has provided the men and women of the fire service with products designed to make their jobs safer and easier.

The independent alternative

Dafo Fomtec AB is a privately owned company with head office in Stockholm Sweden and manufacturing in Helsingborg in the south of Sweden.