Pressure to Perform

Understanding the dynamics of air pressure within your hazmat suit should provide welcome peace of mind.

• By Peter A. Kirk
• Dec 01, 2011

In the fleeting moments while donning a hazmat suit during an emergency situation, it is natural for first responders to feel a sense of anxiety. A host of questions can enter the first responder's mind while preparing to combat both known and unknown chemicals in a hazmat suit: Will I be able to maneuver myself effectively in this suit? How can I be sure the exhaust valves in my suit are working properly? How often does my suit need to be pressure tested?

The answers to these questions lie in understanding the engineering behind your protective garment. While each protective garment is engineered differently, a lot can be understood about the properties and performance of your suit through examining its exhaust valves. Taking the time to consider a suit's valves will not only help first responders to select a hazmat suit, but ultimately provide peace of mind to them when in the hot zone.

For the purpose of this article, we will examine Level A suits, which are built for chemical and gas protection, using a self-contained breathing apparatus (SCBA) for respiration. These suits can be engineered to slightly inflate using the air that is exhaled through the SCBA. The user's exhalation pressurizes the suit, creating a comfortable distance between the emergency responder and the material of the suit.

Ultimately, this design makes the suit more comfortable by decreasing the impact of the suit's weight on the head, shoulders, and mask, which increases user mobility. While inside a suit that is slightly inflated, first responders are more easily able to withdraw their hands for access to radios, gauges, and cloth for wiping a potentially fogged visor.

It is important to note that internal air pressure levels can vary by suit design and manufacturer. The best way to test your suit is by trying it on and checking that there is a comfortable space between your body and the suit's material.

The Potential for User Error
To further understand the dynamics of air pressure within your suit, take time to examine your suit's exhaust valves. There are several types of technology on the market. The most common exhaust valve systems employ a small diaphragm that seats against a set of holes to regulate airflow and prevent leakage of air from outside the suit. This system, while effective, requires diligent maintenance.

Maintenance entails manually dismantling and reassembling each valve to be inspected and pressure tested. This technology should be used with caution because it leaves the potential for user error during the process, posing the threat of inadvertently damaging the valve's diaphragm during testing or reassembling it incorrectly. There is typically no way to accurately verify that the valve has been reassembled correctly and will function as intended during use. This clearly poses a risk because the first responder's protection against inward leakage and harmful gases could be compromised.

To mitigate this risk, it is important to look for hazmat suits with exhaust valves that cannot be disassembled and do not require maintenance. Consider suits that incorporate valves of a completely sealed design. Servicing is not required on closed construction valves, rendering them tamper proof. To be sure your valve is tamper proof, look for a closed construction and verify with your hazmat suit manufacturer that their exhaust valves are 100 percent factory tested against inward leakage and outward flow.

Once you have determined the construction of your valve, take time to examine the material from which the valve is constructed. Valve diaphragms can consist of silicone or more traditional rubber (e.g., butyl), which can cause a difference in shelf life and performance.

Depending on storage conditions, diaphragms made from traditional rubber can become compromised. Extreme temperature fluctuations and dry conditions increase that risk, making the valve diaphragms susceptible to cracking over time. For a more reliable alternative, consider exhaust valves that utilize silicone rubber diaphragms. Silicone is a strong, highly inert polymer, resistant to the effects of environmental exposure. It can be difficult to visually confirm your valve's diaphragm material, so be sure to check with the suit manufacturer for specific information.

Pressure Testing
Even with the highest quality exhaust valves, it is crucial to ensure your hazmat suit is ready for use through routine pressure testing. Requirements for pressure testing are specified through the NFPA 1991 standard. Suits certified to NFPA 1991 must be tested annually or after each time the suit is used (whichever comes first). It is important to point out that exhaust valves requiring disassembly for pressure testing present risk for damaging the valve diaphragm's integrity through user error. To avoid this risk, look for a suit that utilizes permanently sealed construction valves -- they will not need to be disassembled for pressure testing. In addition, some models of exhaust valves, often those with traditional rubber diaphragms, require that the diaphragm be replaced every two years due to manufacturer specifications. This contributes to added maintenance and logistics during the suit’s lifecycle. Be sure to check whether the suit you own or are looking to purchase has such requirements.

Sealing It All In
You can see how exhaust valves, while physically a small component of your suit, are a critical component to your performance, comfort, and ultimate safety while in the hot zone. Whether you are looking to purchase a new hazmat suit or donning an old favorite, understanding the dynamics of your suit should provide peace of mind, which is something every first responder deserves.

This article originally appeared in the December 2011 issue of Occupational Health & Safety.